Range Report Weight Sorted Primer research

[88blazer]

I have weight sorted my primers for years. I decided to test GM215M primers and see for myself if it was worth the time to sort. I used my Dillon Digital scale. I would not recommend a beam scale for sorting....that would take forever.

Savage 110 action
Shilen Select Match .338RUM 28" 9 twist W/Vias brake
Bedded Choate stock and bedded 20moa rail to action
stock trigger

3 fouling shots and last 2 consistent with following group placement.

Three 3 shot groups were loaded. EVERYTHING measure and weight sorted to exact measurements. Brass(trim neck turn and weight), Bullets(ojive and weight) bullet metplat uniform trim prior to weight sorting(oal all the same).

Only thing different was the primer weight. Group 1 at 5.5g, Group 2 at 5.6 and Group 3 at 5.7g. All 9 primers were kept in order and weighed after fired as whole, cup only and anvil weights.

All 9 primers fired weighed in at 5.0g each. Cups at 3.5g and anvils were at 1.4g each. So, there was a .1 to .2g primer compound load difference from primer to primer. All fixed primer components(compound excluded) were exactly the same. The .1g compound difference did make a difference in bullet impact.

All three 3 shot groups were consistant 1" @ 200yds. However;
Group 1 averaged center to bull.
Group 2 was 1/2" averaged off to the left and 1/2" higher.
Group 3 was 3/4" to the left(same average sized group), 1/2" higher
Consistent walk towards 10:00

If no sorting was done, primer differences would have increased my 1" average group(1/2MOA) out to 2"(1MOA). So, standard shooting, no need to sort. ELR Precision and Benchrest, I'll continue to weight sort even match primers. I know now, this is the consistency needed to reach out to 1 mile steel. Every time I don't sort primers, I start seeing flyers again.

Has anybody tested or seen differences like this in other brands of primers other than Federal Match?

 

[James n TN]

Did you shoot these groups over wind flags and shot each round in same conditions? If not then you nulled any potential claim weight sorting primers can adversely change accuracy of a given load.


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[88blazer]

yeah, I had 100 and 200 flags, calm each shot. Same conditions. I also shot the rounds like the OCW test, round 1 group 1, round 1 group 2 and so on. This way, barrel temp was equalized throughout the test. I used my phones stopwatch, one shot every 5 min.

If I could have proved the other way, I would have been much happier. I don't like taking the time to sort primers for my match loads, but these results say to keep doing so. My barrel and chamber might be this picky, other rifles may be more forgiving. Thats something else to consider as well. This was only tested on one rifle so far.

 

[Tempest 455]

Would be interested to see same test w/ chrono numbers.

 

[88blazer]

sucks, cause if I thought about it, the range has loaner chrono's there. Its a PITA, but I might reload 9 more to confirm the data and to chrono the rounds.

 

[James n TN]

I had read elsewhere weighing primers aren't accurate as the main concern is having each primer seated the same depth.
The best bench rest shooters in the world don't even weigh primers. I've sat along side many and watched them dump some on the table and begin loading for there next relays.
I'll dig and see where I did read where sorted primers had no correlation to group sizes.

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[NamibHunter]

Have repeated this test last week. Determined the effect of primer weight on speed. Effect is real, but fairly moderate IF you use a good batch of primers. A bad batch of primers can ruin your day if you compete.

I realize this thread is very old. Will start a new thread.

Namib Hunter

 

[BrentlyWhite]

I stopped weighting primers a long time ago. I did it when I had my 6.5x284. I did not notice a velocity or accuracy difference when shooting the different primer weights. I mostly hunt now so minute of deer is what I aim for although my hand loads are very consistent and accurate.

 

[NamibHunter]

I stopped weighting primers a long time ago. I did it when I had my 6.5x284. I did not notice a velocity or accuracy difference when shooting the different primer weights. I mostly hunt now so minute of deer is what I aim for although my hand loads are very consistent and accurate.

I have come to the same conclusion. Just posted the new thread with some Excel analysis. You should see it under new threads.

Effect is 2.3 fps per milligram of primer weight delta. Not that much, given that in my case (CCI 450) primer weight only varied 5 milligram in total, so around 11 fps of total contribution to MV.

My new goal is to spend less time on fiddly reloading steps, and SHOOT MORE!

 

[NamibHunter]

Minor update: I had some weight sorted primers left over in a box from my last experiment. So decided to use them.... well they have to get used up eventually, for something...

SD was 7.7 fps, over 33 rounds, about the same as what i usually get, plus or minus 1.5. But ES was smaller, 22 fps instead of the usual 35 fps. Might be luck, might not be. My previous calcs showed that other factors dominate, and weight sorting primers in my unique situation would at best lower SD by 1 fps, which is not enough to bother...

But that nice reduction in ES will at least (if repeatable!) reduce that one low and one high impact at 600 or 1000 yards and reduce the size of at least two groups in that range session....

My modified conclusion is that if you could somehow remove the lightest and heaviest 33% of the primers, and shoot only the remaining 67% that your ES will likely come down by about 6-8 fps. In a group shooting competition, that can make the difference between first and third place, but i do not compete - yet.

Unfortunately we do not have an automated sorting machine that can detect the very lightest and the very heaviest of the primers and cull them out... (although thinking about it, posting about the topic might just encourage some vendor to go build one!).... Currently the only (dreadfully slow and mind destroying) approach is to manually weigh every primer, and once you have done that, you can just as well put them into narrow batches... and yes sorting primers into narrow weight groups is overkill, but the problem is mainly that we lack the tools to cull out the worst ones... that would have been sufficient.

 

[RRW]

If I have to resort to weighing primers I'll take up another hobby. I love shooting but not a fan of hand loading but it's a necessary evil I guess. I am not a good enough shooter to tell anyway and the type of shooting I do it wouldn't make a difference but if you are that anal that you need to weigh primers, have at it.

 

[Steel head]

Weighing primers?

 

[Milo 2.5]

Weighing primers?
View attachment 7203363

LMAO, it is a thing, and in the right circles generates some serious conversations-arguments. I'm pretty sure some guys gave up over on accurate shooter after being ridiculed about this.
I think the key for me I guess is having or knowing the balance of what I will or wont do to make a satisfactory load.
Common sense says if the only way to bring your load into a satisfactory position is to weigh primers, it is time to move on.

 

[308pirate]

How in the fuck do these people know if the weight variation is due to the variation in priming compound fill or just the inherent variation in sheetmetal thickness from which the cup and anvil are made?

How can they be so absolutely sure that they've nulled out all other variables? Because I KNOW nobody doing these "experiments" knows how to do a multivariate designed experiment.

EL-OH-FUCKING-EL

 

[nn8734]

Little while ago, I decided to weigh a batch of 210M primers just for the purposes of controlling for overall brass weight across a particular batch of primed brass and found all 20 weighed were 4.5 grains. In my case just wanted to see if federal cots brass weighted the same as the mil brass (.300 win mag) (i later just weighed unprimed brass and found no material weight differences)

My thoughts on the efficacy of primer sorting mirror 308Pirate’s in that there are so many other variables that impact MV consistency and other aspects of performance to the extent primer weights have a very low probability of establishing a material impact on a particular load, at least for practical shooting.

Maybe benchrest guys would derive a measurable value from the effort.

 

[Steel head]

How in the fuck do these people know if the weight variation is due to the variation in priming compound fill or just the inherent variation in sheetmetal thickness from which the cup and anvil are made?

How can they be so absolutely sure that they've nulled out all other variables? Because I KNOW nobody doing these "experiments" knows how to do a multivariate designed experiment.

EL-OH-FUCKING-EL

 

[NamibHunter]

If I have to resort to weighing primers I'll take up another hobby. I love shooting but not a fan of hand loading but it's a necessary evil I guess. I am not a good enough shooter to tell anyway and the type of shooting I do it wouldn't make a difference but if you are that anal that you need to weigh primers, have at it.

Have to agree with you.

I have given up on weight sorting primers, not enough of a benefit for what i am trying to do.

Have an engineering background, and occasionally like to run a properly designed experiment to either confirm or debunk one of the dearly beloved assumptions of the reloading game.... kind of a side hobby. Came to the conclusion that lot of what the fully indoctrinated OCD reloader is doing is actually NOT beneficial (or least not beneficial enough outside of the BR game) to warrant the time some hunters or tactic shooters spend on it.

For example: Ran a rather extensive experiment to figure out if weight sorting cases are worth it or not. So i collected 6.5 CM range brass of different brands, fire formed them, measured water volume, weighed them, and then fired them and observed speed. Confirmed that case weight and case volume correlates 95%, at least for the 6 or 7 brands that i worked with, and that there is no need to measure water volume, as case weight is an adequate stand-in. I was surprised by this result, but it was very solid. Poorly made brass might well have variations in the web area, but this was not present in the cases i collected. Some folks will never accept that, but they never run their own experiments either, yet maintain strong opinions handed down from others. Proved to myself that top quality bras does not benefit from weight sorting. [Also confirmed that culling out the lightest and heaviest brass in a less than stellar brass batch is justified, but have given up on inconsistent brass. Pay the extra money for Lapua, Alpha or Peterson brass and save yourself a lot of unnecessary aggregation.] Yes all these minor affects do add up and will collectively have change your group size, but there are only diminishing returns here.

So i am on a journey to simplify my reloading steps until SD degrades to 9.99 fps, and group size opens up to 0.5”. Ideally want to load in half the time or less. ? Want to shoot more, because i am without doubt the weakest link in the system. If ever i decide to compete, i will still do the best job i can... but that is for much later.

 

[NamibHunter]

View attachment 7203386

Fair question!

Well, i measured 10 primers before and after firing and confirmed that about 80% of the primer weight variation is in the primer compound, not the metal. Others who have run this experiment came to the same conclusion.

The main point though is that the factory does a pretty good job with their quality control. If you are in the BR game, i guess go ahead and sort your primers. But my data set convinced me that hunters and tactical shooters can skip primer weight sorting. [But if the factories ever start to slip on their quality control, this recommendation might need to be changed. Low probability though.]

 

[308pirate]

Well, i measured 10 primers before and after firing and confirmed that about 80% of the primer weight variation is in the primer compound, not the metal

Interesting...….questions that come to mind

• How does one account for the mass of combustion by products left in the cup?
• What's the resolution of the scale used?
• When was the last time the scale was calibrated to a NIST standard?
• What were the effects of environmentals on the scale, or how does your scale compensate for them?
• What's the % repeatability and % reproducibility of your scale? Basically was a proper gauge R&R study done?

 

[morganlamprecht]

if you weigh primers...in 3 different cartridges

in every cartridge tested, the higher the primer weight...the higher the average velocity for each lot, with virtually no overlap

what do you want to call it? because i dont care, i dont weigh primers for typical reloading

 

[NamibHunter]

Interesting...….questions that come to mind

• How does one account for the mass of combustion by products left in the cup?
• What's the resolution of the scale used?
• When was the last time the scale was calibrated to a NIST standard?
• What were the effects of environmentals on the scale, or how does your scale compensate for them?
• What's the % repeatability and % reproducibility of your scale? Basically was a proper gauge R&R study done?

These are all good questions.

Nope i am not running a metrology lab (yet), so FX120i scale is calibrated to a cheap reference weight that i purchased many years ago. So likely repeatable to 0.02 grains, but absolute accuracy cannot be proven. Scale was used in milligram mode as that is a tiny bit more accurate. [Perhaps do a search, i posted on the topic here before, more details there.] Scale holds zero pretty well once up to temperature and if you prevents drafts, so turn off the AC, keep the draft screens up, and close the door of your reloading room. I did weigh 50 or so twice, and found only roundoff errors.

Yes: The combusted primer compound left in the primer cup is troublesome. Have to take the used primer apart and scrape the ash out. Otherwise the results are wildly inaccurate.

Short summary is that i cannot detect an improvement in SD, maybe 1 fps, but qualitatively, there might be a useful improvement in ES (Since ES is often 4-5x bigger it stands out more). Stats says the SD reduction result is inconclusive. If my SD was around 2-3 fps already i guess i would have seen it, but i get 6-9 fps most days. Anyway, if the effect (in your own unique situation) is not strong enough to jump out at you, how can it be of much practical benefit, so i have moved on to other issues/challenges.

Clearly I have other bigger problems that dominate my SD...

Picture below: Primer components. The ash has to come out before weighing the metal components and subtracting from the original unfired weight.

 

[308pirate]

These are all good questions.

Nope i am not running a metrology lab (yet), so FX120i scale is calibrated to a cheap reference weight that i purchased many years ago. So likely repeatable to 0.02 grains, but absolute accuracy cannot be proven. Scale was used in milligram mode as that is a tiny bit more accurate. [Perhaps do a search, i posted on the topic here before, more details there.] Scale holds zero pretty well once up to temperature and if you prevents drafts, so turn off the AC, keep the draft screens up, and close the door of your reloading room. I did weigh 50 or so twice, and found only roundoff errors.

Yes: The combusted primer compound left in the primer cup is troublesome. Have to take the used primer apart and scrape the ash out. Otherwise the results are wildly inaccurate.

Short summary is that i cannot detect an improvement in SD, maybe 1 fps, but qualitatively, there might be a useful improvement in ES (Since ES is often 4-5x bigger it stands out more). Stats says the SD reduction result is inconclusive. If my SD was around 2-3 fps already i guess i would have seen it, but i get 6-9 fps most days. Anyway, if the effect (in your own unique situation) is not strong enough to jump out at you, how can it be of much practical benefit, so i have moved on to other issues/challenges.

Clearly I have other bigger problems that dominate my SD...

Awesome. Seldom do I come across a reloader that actually understands true measurement and uses hard data to drive decisions.

Maybe revisit the effect primer weight variation has on extreme spread later when other lower hanging fruit's been picked clean.

 

[nn8734]

@NamibHunter can we assume you already tested other primers with the load in question to address the issues you mention having with your SD?

 

[NamibHunter]

@NamibHunter can we assume you already tested other primers with the load in question to address the issues you mention having with your SD?

Tested CCI450 and Federal GM205M primers, in the same 6.5 CM rifle, with similar results as far as fps per gram of primer weight increase. [Other folks have achieved similar results.]

https://www.snipershide.com/shooting/threads/effect-of-primer-weight-on-speed.6968552/

I have so far only experimented with CCI450 and GM205M primers in SRP brass (Lapua and Alpha brass). ES and SD results (and group size) were quite similar. Was hoping that GM205M will help to achieve a lower ES, but that did not materialize.

One untapped possibility is to try other brands of primers. Any suggestions?

Concentricity improvements, and more constant neck tension (or consistent but much higher higher/lower) neck tension could also be useful directions to go.

 

[NamibHunter]

Awesome. Seldom do I come across a reloader that actually understands true measurement and uses hard data to drive decisions.

Maybe revisit the effect primer weight variation has on extreme spread later when other lower hanging fruit's been picked clean.

Yep that is a good idea.

I would love to get my ES below 25, but primer weight was not the ticket.

Bought a Teslong bore scope, and found a (minor) carbon ring in the chamber, in the neck area, which might have caused a slight pinch, as a few cases were shorter than trim length, and two were long. Oversight. Scrubbed out the carbon ring, and trimmed them all equally short. Now trim every time, on a more accurate Wilson trimmer. ES is now 25-32 fps range. A nice improvement, but more remains to be done.

Now looking for the next useful improvement.... It seems the rifle does better with high neck tension, so trying a (very) slight crimp, and a smaller button in the die (Whidden FL die with a set of different size buttons). Excessive neck tension has its own problems it seems. If i resize the neck too much, it gets small enough to cut the pressure ring clean off the bullet during the seating step, which i am sure is a bad idea... so crimp option seems less damaging. Using a Lee crimp die.

 

[Steel head]

Good idea.

I would love to get my ES below 25, but primer weight was not the ticket.

Bought a Teslong bore scope, and found a (minor) carbon ring in the chamber, in the neck area, which might have caused a slight pinch, as a few cases were shorter than trim length, and two were long. Scrubbed out the carbon ring, and trimmed them all equally short. ES is now 25-32 fps range. A nice improvement, but more to be done.

Now looking for the next useful improvement.... It seems the rifle does better with high neck tension, so trying a slight crimp...

two questions
What are you measuring ES/SD with?

do you have issues with vertical at distance?

 

[nn8734]

Tested CCI450 and Federal GM205M primers, in the same 6.5 CM rifle, with similar results. Other folks have achieved similar results.

https://www.snipershide.com/shooting/threads/effect-of-primer-weight-on-speed.6968552/

Gotcha, I skimmed it and looks like an interesting read (I enjoy load development and getting into the details)....I’ll read through it when I have some time.

Edit: questions largely answered in post 28.

 

[NamibHunter]

two questions
What are you measuring ES/SD with?

do you have issues with vertical at distance?

Labradar, which i have compared with a MagnetoSpeed, and their SD and ES numbers were very close. So i think the Labradar is good.

Yes i do get vertical stringing at 600 yards. Have figured out how to pick a load that exploits positive compensation, so shots that are 10 fps below or above the average hits within 1.5” of the same “waterline”, which i think is pretty good, but the odd one that is 25 fps too fast, which increased ES a lot, takes me up sometimes 3-4”, and then the gun shoots over the smaller gongs.

Target 1 below is better than typical, but is a good example, as it shows 4 close impacts at 500 yards, and one 2” higher that i am pretty sure was not me. Speed was around 20 fps higher than average.

Target 2 shows what happens in high wind (12-16 mph). Did not compensate for wind speed. High berm behind the target, and wind is nearly parallel with the shooting lane, then blows over the high berm and likely lifts the bullet some amount. My typical group at 600 is a rotated oval, and seems to correlate with wind speed. Yes my wind reading skills still suck... Might be or might not be vertical stringing....

 

[Steel head]

Well I trust your instrumentation.

One thing I do is mark cases that show odd swings.

I have found cases that are repeat offenders.

 

[NamibHunter]

Gotcha, I skimmed it and looks like an interesting read (I enjoy load development and getting into the details)....I’ll read through it when I have some time.

Couple questions: have you taken measurements of factory match ammo from your rifle? If so, which ammo and how did it perform (mean MV, SD, ES)?

Also, have you shot your developed loads at 300 yards? What did the vertical dispersion look like, if so?

Recently tested Berger 140 Hybrid factory ammo, it is loaded in Lapua SRP brass and one box gave an SD of 12, another was around 8-9 fps, which is superb for a factory offering. The 100 yard groups were 0.3” to 0.45”, for three shot groups. Typical 5 shot group was 0.55”, which i think is good.

So i replicated the seating depth of 2.8”, book length, and it will fit the Pmags, but they must use some proprietary powder and i could bot match the speed (2820 fps) without pressure signs. MPA rifle has a fairly tight chamber. I get 2720 fps max with H4350 and then get full moon ejector marks beyond that.

Yes, here are some 300 yard groups, which were all sub MOA.

 

[nn8734]

@NamibHunter

Above groups look good. I’m assuming your 2.8 above is the base to ogive length?

Have you tried Remington primers?

Not sure about their SRP counterparts but I often switch back and forth between F210M and Rem 9 1/2 once I have a single digit SD to see if I can drive it lower. The F210M is a little hotter than the Rem 9 1/2 (many of CCI primers are said to be “in between”.). I do this when loading for my .308s, 300WM and .338 Lapua. There is usually a clear difference between one or the other for whichever load I’m developing across all of those rifles.

Also, do you measure the case diameter just above the extractor grove after sizing but before assembly/firing your test rounds?

 

[NamibHunter]

Replies in your text below:

“Above groups look good. I’m assuming your 2.8 above is the base to ogive length?”

N: COAL, 6.5 CM has a shorter case.

“Have you tried Remington primers?“

N: Not yet, will give it a go!

“Not sure about their SRP counterparts but I often switch back and forth between F210M and Rem 9 1/2 once I have a single digit SD to see if I can drive it lower. The F210M is a little hotter than the Rem 9 1/2 (many of CCI primers are said to be “in between”.). I do this when loading for my .308s, 300WM and .338 Lapua. There is usually a clear difference between one or the other for whichever load I’m developing across all of those rifles.”

“Also, do you measure the case diameter just above the extractor groove after sizing but before assembly/firing your test rounds?”

N: No, can you explain the objective? I do check primer pocket diameter. Still tight.

 

[nn8734]

“Also, do you measure the case diameter just above the extractor grove after sizing but before assembly/firing your test rounds?”

N: No, can you explain the objective? I do check primer pocket diameter. Still tight.

Ye I toss brass with loose pockets.

As far as that case measurement, I do it for two reasons:
Reason 1
Detect variance in case diameter across sized cases before loading so I know every case has the same dimension

For example, my .300 wm cases are all .512 just above the belt after f/l sizing and belt sizing, for the most part. Cases not of this dimension are put in a separate bin based on their measured dimension. This simply eliminates one more potential area of variability and is easy and quick to do (I usually sit in front of the TV and measure 100-200 cases at a time) and throw them into a few different bins based on the different sub populations that arise. Generally, 80-90% of cases have the same dimension with the rest which I consider “deviants” and attempt to size them to dimension that matches the main population.

Reason 2
2) Determine when I’m at pressure. After firing each round in a test lot, I measure the case in the exact same area to see how much it expanded. Any expansion > .0015 tells me I’m at pressure. Beyond .0025-.003, I start to see visible pressure signs on the case head, primer, etc.

Here are some pics illustrating what I’m talking about

In the above, the pre-fired case measured .512 (my mic shows a hair over but I was holding it with one hand and it slipped a bit)

The fired case below shows .513 or .001 expansion, which is fine. No visible pressure signs on the case head.

Experiment
I did an experiment where I loaded ten cases exactly the same (190 smk .030 jump, 77.1g h1000, full length size Federal case, Fed 210M) but divided them into two groups. The first group had no variability in case dimension as measured above. The second group had up to .002” case variability (one case was .514, two were .513 and two were .512). All Cases were previously weight sorted and bullets were previously ogive sorted and I made absolutely sure to choose cases that weighed exactly 255 grains and bullets with ogives that measured 1.78” with the Sinclair bullet comparator. All cases were sized to exactly .0005” cartridge to chamber headspace. Neck tension was .004 for all 10 rounds.

After taking a fouling shot, I fired each of them slowly at a 300 yard target over LabRadar and collected the following data for each group:

measurable	Group A (no case variability)	Group B (case variability)
SD	8.2	12.7
ES	16	33

The groups themselves were not substantially different looking. Ave MV was 3067 for group A and 3059 for group B.

After controlling for all other variables to the fullest extent possible, there is a material difference in SD/ES between the two groups.

My initial hypothesis is that variability in case dimension in that location may be driving SD/ES values up. I will be doing more testing to confirm/deny either this weekend or after Christmas. I will also be evaluating runout as a possible driver once I get a good run out gauge set up.

Long winded but hope that explains it. It’s perhaps another source of variability in load performance to consider. Feel free to ask any questions.

 

[NamibHunter]

Ye I toss brass with loose pockets.

As far as that case measurement, I do it for two reasons:
Reason 1
Detect variance in case diameter across sized cases before loading so I know every case has the same dimension

For example, my .300 wm cases are all .512 just above the belt after f/l sizing and belt sizing, for the most part. Cases not of this dimension are put in a separate bin based on their measured dimension. This simply eliminates one more potential area of variability and is easy and quick to do (I usually sit in front of the TV and measure 100-200 cases at a time) and throw them into a few different bins based on the different sub populations that arise. Generally, 80-90% of cases have the same dimension with the rest which I consider “deviants” and attempt to size them to dimension that matches the main population.

Reason 2
2) Determine when I’m at pressure. After firing each round in a test lot, I measure the case in the exact same area to see how much it expanded. Any expansion > .0015 tells me I’m at pressure. Beyond .0025-.003, I start to see visible pressure signs on the case head, primer, etc.

Here are some pics illustrating what I’m talking about

View attachment 7203950View attachment 7203951
In the above, the pre-fired case measured .512 (my mic shows a hair over but I was holding it with one hand and it slipped a bit)

The fired case below shows .513 or .001 expansion, which is fine. No visible pressure signs on the case head.

Experiment
I did an experiment where I loaded ten cases exactly the same (190 smk .030 jump, 77.1g h1000, full length size Federal case, Fed 210M) but divided them into two groups. The first group had no variability in case dimension as measured above. The second group had up to .002” case variability (one case was .514, two were .513 and two were .512). All Cases were previously weight sorted and bullets were previously ogive sorted and I made absolutely sure to choose cases that weighed exactly 255 grains and bullets with ogives that measured 1.78” with the Sinclair bullet comparator. All cases were sized to exactly .0005” cartridge to chamber headspace. Neck tension was .004 for all 10 rounds.

After taking a fouling shot, I fired each of them slowly at a 300 yard target over LabRadar and collected the following data for each group:

measurable	Group A (no case variability)	Group B (case variability)
SD	8.2	12.7
ES	16	33

The groups themselves were not substantially different looking. Ave MV was 3067 for group A and 3059 for group B.


After controlling for all other variables to the fullest extent possible, there is a material difference in SD/ES between the two groups.

My initial hypothesis is that variability in case dimension in that location may be driving SD/ES values up. I will be doing more testing to confirm/deny either this weekend or after Christmas. I will also be evaluating runout as a possible driver once I get a good run out gauge set up.

Long winded but hope that explains it. It’s perhaps another source of variability in load performance to consider. Feel free to ask any questions.

Impressive to see experimental data on this topic. Have a micrometer, so will have a look.

 

[NamibHunter]

Ye I toss brass with loose pockets.

As far as that case measurement, I do it for two reasons:
Reason 1
Detect variance in case diameter across sized cases before loading so I know every case has the same dimension

For example, my .300 wm cases are all .512 just above the belt after f/l sizing and belt sizing, for the most part. Cases not of this dimension are put in a separate bin based on their measured dimension. This simply eliminates one more potential area of variability and is easy and quick to do (I usually sit in front of the TV and measure 100-200 cases at a time) and throw them into a few different bins based on the different sub populations that arise. Generally, 80-90% of cases have the same dimension with the rest which I consider “deviants” and attempt to size them to dimension that matches the main population.

Reason 2
2) Determine when I’m at pressure. After firing each round in a test lot, I measure the case in the exact same area to see how much it expanded. Any expansion > .0015 tells me I’m at pressure. Beyond .0025-.003, I start to see visible pressure signs on the case head, primer, etc.

Here are some pics illustrating what I’m talking about

View attachment 7203950View attachment 7203951
In the above, the pre-fired case measured .512 (my mic shows a hair over but I was holding it with one hand and it slipped a bit)

The fired case below shows .513 or .001 expansion, which is fine. No visible pressure signs on the case head.

Experiment
I did an experiment where I loaded ten cases exactly the same (190 smk .030 jump, 77.1g h1000, full length size Federal case, Fed 210M) but divided them into two groups. The first group had no variability in case dimension as measured above. The second group had up to .002” case variability (one case was .514, two were .513 and two were .512). All Cases were previously weight sorted and bullets were previously ogive sorted and I made absolutely sure to choose cases that weighed exactly 255 grains and bullets with ogives that measured 1.78” with the Sinclair bullet comparator. All cases were sized to exactly .0005” cartridge to chamber headspace. Neck tension was .004 for all 10 rounds.

After taking a fouling shot, I fired each of them slowly at a 300 yard target over LabRadar and collected the following data for each group:

measurable	Group A (no case variability)	Group B (case variability)
SD	8.2	12.7
ES	16	33

The groups themselves were not substantially different looking. Ave MV was 3067 for group A and 3059 for group B.



After controlling for all other variables to the fullest extent possible, there is a material difference in SD/ES between the two groups.

My initial hypothesis is that variability in case dimension in that location may be driving SD/ES values up. I will be doing more testing to confirm/deny either this weekend or after Christmas. I will also be evaluating runout as a possible driver once I get a good run out gauge set up.

Long winded but hope that explains it. It’s perhaps another source of variability in load performance to consider. Feel free to ask any questions.

Reread it today, and this is a fascinating result. If the case post firing has bigger dimensions post firing, it would indicate the case has been exposed to higher pressure OR the metallurgy/grain structure is different in the web area (allowing the case to expand a tiny bit more, so it stretched 2 thou more, or the springback is different, which also point at different brass hardness).

If the cases were all loaded with the exact same amount of powder, and the powder is uniform (same burn rate from one case to the next, so powder is uniform or at least well mixed), then maybe you have devised a clever way to measure brass properties around the case web, which might well affect how the bottom half of the case grips the chamber (the part that never gets annealed)... So maybe Lapua and their competitors ship us cases that do not have exactly the same metallurgical properties (e. g. Young modulus, resistance to expansion). Just speculation at this point, but there might be more going on than just a volume difference during the 2-3 microseconds before the case expands to chamber dimensions... which is likely a small effect compared to a case that slips more rearwards before the brass grips the case walls, changing effective bullet jump, and once the bullet seals off the bore when it engraves the lands, the additional volume in the chamber can now be very different while thr pressure ramps up to the point where the “stuck” (engraved) bullet becomed unstuck and starts sliding down the barrel. I think there is a bigger volume delta based on where the brass finally grabs the chamber and stop moving rearward...

Not trying to start an argument!

Your approach might well inform the reloader on what brass to cull because it has different brass properties, either hardness or springback, (heck, whatever the physical mechanism actually is!).

 

[nn8734]

Not trying to start an argument!

All good, didn’t see anything argumentative. While I’m not an engineer or metallurgist, the physical analysis is actually very intriguing and helps understand the physics behind what’s actually happening to the brass in the chamber and corresponding impacts on the chamber pressure curve. If only I had the test equipment to measure and graph the chamber pressure from initial ignition to when the bullet seats fully into the lands from round to round, we’d have some crucial data to help confirm/deny your theory as well as quantify the change in bullet jump from its pre-ignition distance although the delta may be more material to secant ogives relative to tangent in terms of precision on paper. I believe such equipment exists but it’s very expensive.

All cases were definitely loaded with exactly 77.1g and H1000 is cut pretty dimensionally consistent as far as stick powder is concerned so we can prob assume the burn rate from round to round had minimal variance. Not to mention it’s also considered the coolest, cleanest most consistent burning of all the slow burn rate magnum powders so would be an ideal powder for this type of experiment.

It’s worthy of further RDTE, if for no other reason but to eliminate potential sampling error muddling the results.

Like you, I try to finely control for as many variables as prudent (ie where the juice is worth the squeeze in terms of measurable results). And I think your right about using the measurements to cull brass, given that variances in expansion technically shouldn’t occur if the brass is perfectly uniform in its constitution in that area across all pieces for a given manufacturer.

 

[NamibHunter]

Replies below.

“While I’m not an engineer or metallurgist, the physical analysis is actually very intriguing and helps understand the physics behind what’s actually happening to the brass in the chamber and corresponding impacts on the chamber pressure curve. If only I had the test equipment to measure and graph the chamber pressure from initial ignition to when the bullet seats fully into the lands from round to round, we’d have some crucial data to help confirm/deny your theory as well as quantify the change in bullet jump from its pre-ignition distance although the delta may be more material to secant ogives relative to tangent in terms of precision on paper. I believe such equipment exists but it’s very expensive.”

N: You can a partial measurement via the Pressure Trace system:

Rifle Barrel Chamber Pressure Testing Hardware & Software | Pressure Trace

Measure ACTUAL rifle chamber pressure for each shot, barrel harmonics, rise time, time to muzzle exit and OBT barrel timing.

www.shootingsoftware.com

It is about $800 (electronics plus strain gauge set).



“All cases were definitely loaded with exactly 77.1g and H1000 is cut pretty dimensionally consistent as far as stick powder is concerned so we can prob assume the burn rate from round to round had minimal variance. Not to mention it’s also considered the coolest, cleanest most consistent burning of all the slow burn rate magnum powders so would be an ideal powder for this type of experiment.”

N: Then we probably have to conclude that the change in base diameter is due to changes in brass (material) properties

“It’s worthy of further RDTE, if for no other reason but to eliminate potential sampling error muddling the results.”

BTW: Many short range BR competitors believe that 6PPC outperforms all other options in their game because of the way the brass consistently grips the walls of the chamber. Somehow the 220 Russian and 6PPC cases have something magical about its dimensions and brass thickness that makes it perform so well. Nobody knows exactly what....

“Like you, I try to finely control for as many variables as prudent (ie where the juice is worth the squeeze in terms of measurable results). And I think your right about using the measurements to cull brass, given that variances in expansion technically shouldn’t occur if the brass is perfectly uniform in its constitution in that area across all pieces for a given manufacturer.”

N: My conjecture may be way off, or not, who knows.... but if these expanded cases always have worse ES and SD, then culling them makes a lot of sense. Whatever the physical mechanism at work here. I will try it! In fact i wil try almost anything to get my ES into the mid to low twenties...

 

[nn8734]

Replies
N: You can a partial measurement via the Pressure Trace system:

Rifle Barrel Chamber Pressure Testing Hardware & Software | Pressure Trace

Measure ACTUAL rifle chamber pressure for each shot, barrel harmonics, rise time, time to muzzle exit and OBT barrel timing.

www.shootingsoftware.com

It is about $800 (electronics plus strain gauge set).

NN8734: That’s not bad....hmmm

N: Then we probably have to conclude that the change in base diameter is due to changes in brass (material) properties

NN8734: Assuming all controllable production and testing variables are controlled for, I’m inclined to agree

N: My conjecture may be way off, or not, who knows.... but if these expanded cases always have worse ES and SD, then culling them makes a lot of sense. Whatever the physical mechanism at work here. I will try it! In fact

NN8734: Agree with this as well.

N: i wil try almost anything to get my ES into the mid to low twenties...

Me too, man....lose sleep at night if I can’t get a load dialed in right, lol...Here are my performance standards for a production-ready load as measured across 10 randomly selected rounds for that load. Applies to bolt guns only, I keep a different set of benchmarks (same KPIs) for my gas guns.

SD: <=10
ES: <= 2x SD
Vertical Dispersion at 90% average max effective range (MER) <= 1 MOA

Example: If a 308 Win load’s MER=1000 yards then vertical dispersion @ 900 yards must be <= 9”.