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Effect of case volume on 6.5 Creedmoor velocity - some experimental data

NamibHunter

Desert hunter
Full Member
Minuteman
Dec 26, 2018
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OK, have been wanting to run this experiment for a while, and finally found the time 2 weeks ago. Have been collecting range brass over the past 4 years and just kept it in a plastic bucket, never shot it since it is unsorted, different manufacturer, different batch and different weight. Would not be wise (or safe) to mix and match brass. My main question was: How much do you have to back off on powder charge if you switch to much thicker heavier brass?

Went through the 1000 or so i have and selected 3 to 5 of each make: Hornady, Nosler, Winchester (probably the same as Hornady?), Prime, Federal, Sig, and Norma. [Lapua was excluded because it is a small rifle primer case, and did not want to pick up speed differences due to primer changes.]

Neck turned all of them to 0.0125” (12.5 thou). Trimmed all of them to 1.908” as some were quite short and some were quite long, well beyond trim length. Chamfered and deburred, cleaned primer pockets, tumbled for 2 hours (fairly clean). Idea was that the necks must not contribute to weight differences (bullet takes up most of the neck volume before ignition starts, so reasoned neck’s impact is less inportant). Later results seem to confirm this.

Always wondered if weight differences are mainly caused by wall thickness variation vs. variations in the web thickness. Cases were not yet deprimed, so could measure case volume for a few of them. Used 91% rubbing alchohol to measure case volume on a lab scale to within 0.04 gn. Used a rubber plug to close off the neck so it will not leak or spill once on the scale, and this reduced minuscus errors, as the excess liquid would spill out of the case when the plug is slipped over the neck (on the outside), then dried the case with a cloth. Alchohol evaporates quickly, so a clean operation, just lots of fumes to deal with. Good ventilation helps. It is easy to calculate alcohol weigth (and therefore volume) from the difference in weight between an empty dry case, and the same case filled with liquid. Liquid seems to fill up the primer pocket as well due to the low viscosity of alchohol.

Found a remarkably accurate correlation between case weight (considering one make of brass at a time) and case volume: Straight line least squares fit had a R-square of 0.95 meaning the best straight line fit could ascribe 95% of the case volume variation to the case weight differences. Concluded that the weight of the liquid needed to fill a case could be adequately inferred via case weight, which is much faster to do. Differences in web thickness did not appear to cause major differences in this linear relationship (so no real issue with thick web and thin case wall combos), at least for the brands and batches that I tested. [This will not be true for poorly made brass.]

Hornady brass (from different batches) varied from 143.0 grain to 154.5 grain, a difference of 11.5 gn, which is quite significant.

Norma brass varied from 153.8 to 155.2 gn, a delta of 2.4 gn (which is far better than Hornady), but all from one batch, and the batch was small (50).

Winchester brass varied from 148.1 to 150.0 gn, a delta of 1.9 gn. Prime stamped brass was around 155 gn. with fairly low variation.

Notably, Nosler brass had a very narrow weight range (160.4 to 160.9) for this random sample of 5, but it was quite a bit heavier than other brands. Maybe that explains why it lasts 2x longer than Hornady brass in terms of max nr of reloads? Nosler claim to sort by weight before they ship, and that appears to be true.

Sig stamped brass was around 155 gn on average.

The heaviest brass was Federal at 172 gn, which is a very significant difference from Hornady at 143-155 gn. Federal brass is a good 15% heavier than Hornady. [Anybody who has experience reloading Federal brass: How long do they last?]

Next selected 2-4 pieces of brass from different manufacturers to span the widest possible weight range and get enough data points for an Excel analysis. Weight range was from 143.00 to 172.28 gn. We all know you cannot load heavy thick walled brass to the same max load as thin walled brass, so i tried to be conservative and reduced powder charge from a max of 41.6 gn (for my rifle) to 40.0 gn of H4350 and loaded 140 gn Hornady ELD Match bullets, all weight sorted to be within 0.1 gn. Scale is an AND FX120i lab scale capable of measuring to 0.02 gn. Used a Labradar to capture speed. Should be pretty accurate.

Federal GM210M large rifle match primers were used, all from the same batch. This batch gave good results before. Brass was full length resized in a Redding type S die, and shoulders were bumped back by 0.003”. Neck tension was fairly light (same bushing, same neck wall thickness due to neck turning, Sinclair mandrel die used to open up the necks and get them more concentric), as that gave the best accuracy before.

Bullets were intentionally loaded long (0.150”) to force all bullets to soft seat as the bolt was closed. All cases closed very easily, due to low neck tension. Net result would be a small (but unknown) amount of bullet jam.

Results: Plot of speed vs case weight formed an almost perfect straight line, with the lightest cases (143 gn) achieving 2699 fps, and the heaviest Federal cases (173 gn) getting to 2759 fps from a 30” Shilen Match Select barrel. This is about the same speed than i typically get with 41.5 gn of the same powder with Lapua cases, for the same 140 gn bullet. [Higher than expected speed from the Federal case was clearly caused by the 15% lower case volume. Jamming the bullet was also a contributing factor, likely to a lesser extent.]

Speed difference between lightest (143 gn) and heaviest case (173 gn) was 60 fps, which is significant. According to Excel, we gain 2.2 fps per grain of additional case weight, at these relatively low speeds (for a 30” barrel). Statistical fit was good: R-square was 0.97, after rejecting one outlier which was way off (possibly a user mistake).

Wondered if the soft seating was affecting my results too much, so repeated the experiment with 140 ELD-M loaded to book length (2.80” COAL), about 0.050” jump. Used the same brass as before, this time body sized then neck sized (equivalent to FL sizing), same powder charge, speed varied from 2653 to 2749 fps. R-square was less impressive this time, at 0.89, but still adequate. Excel said we now gain 3.04 fps per grain of case weight.

Repeated the experiment a third time at max load (will try to avoid mentioning powder charge or exact speeds). A small nr of half moons appeared on the case heads, and flat primers, indicating pressure was probably getting too high. Speed increment per gn of case weight increase was much less than before, at 1.2 fps per grain. This is in line with published BR experience: There comes a point where speed will not increase anymore. Degree of fit was also very poor (Rsquare of 0.37) indicating other random factors (e.g. the case not adequately gripping the chamber every time, and moving backwards to make contact with the bolt face). Also hints that shooting max loads might not be the most accurate approach (SD will open way up).

Last experiment: Tried neck sizing only (once fired since last full length resizing), 40.0 gn of the same batch of H4350, same 140 gn ELD-M bullet, loaded to book length. Speed gain was 2.12 fps/gn of case weight increase, very similar to the previous result i got with FL sizing. Speed range was 2656 fps to 2725 fps. Seems to indicate that neck sizing leads to lower speed (expected, case has more volume prior to expansion and prior to gripping the chamber), but that the speed gain vs case weight increase is almost identical between FL and neck sizing. Rsquare was 0.895, which is good. [One possible outlier was kept. Nice straight line except for the one data point.]. Around 70 fps speed gain going from a light Hornady case to a heavy Federal case. Same delta speed result as before (as long as you are well away from max loads).

What can we do with data like this? Some (possibly useful) conclusions:

1) Good quality brass is available (like Nosler and Lapua) that does not need to be weight sorted for shooting at steel targets at 600 yards. But if you want to get a further reduction in SD, you will likely gain a little bit (1-3 fps) by at least culling the very heavy and very light cases from your chosen 50. If the large batch varies by 3-4 grain (Hornady, Winchester), speed impact is 6-12 fps if we believe my Excel result, which is still OK at 400 but not OK at 1000 yards, so weight sort your (economy) brass. Takes only an hour or so, so worth it.

2) If you compete, or you are trying to shoot the smallest possible 5 shot groups (<0.35”) or trying to improve on your personal best, then weight sort your brass into groups of 5 that have very similar case weight and serialize your brass (each get a number, via a permanent marker or an engraver, stick to the web area where the case is very thick, use small letters or numbers so it does interfere with a concentricity guage). Yes this is a pain and takes a lot of time. And people look at you funny. Then sort your loaded ammo based on serial number. I don’t always do this, it depends what i am trying to accomplish (e.g. this is pointless on hunting ammo). When i shoot beyond 500 yards at very small targets, i do this and also cull the loaded ammo based on a concentricity check. In my experience, SD comes down from the 8-12 range to the 5-9 fps range. Not always a huge improvement (there are other factors too), but enough to push up your hit percentage on small steel targets, and it helps when you are shooting groups at diatance. Best 4 shot group at 500 yards = 0.97”, but that has only happened once. Typical result is 1.2-2.5”. Wind is the enemy.

3) At least for the brands of brass that i tested, case weight after decapping, trimming and and tumbling is a good proxy for case volume. Consider buying cases in bulk (200 plus) to get the same batch, then trim to length (neck turn if you want, or skip), weigh them all, and then sort your brass into a batch of 50 with the narrowest weight range you can get from that batch. There seems to be little benefit in measuring actual case volume, which is slow and messy if you use water. Water dripping through the electronics inside your scale is probably a bad idea.

4) Avoid max loads, as speed variations (SD) becomes excessive, and the increased SD will cause large vertical spread at distance. Probably best to reload for the second highest ‘node’ and avoid the top node. Watch out for thick walled (heavy) range brass, and calculate how far you will have to back off on powder charge, start low and increase in small increments.

5) The sensitivity factor that relates speed to case weight is somewhere between 2.1 and 3 for my rifle (30” barrel), and it seems to depend on the speed range. The slower the speed, the higher the factor. Your results will likely be different.

If i want SD below 10 fps, then assuming half the variation comes from case volume and the remainder from other sources (bullet weight, bearing surface, barrel fouling, barrel temperature, ambient temperature), then i can only afford 5 fps variation due to case volume/case weight differences. That means between 5/2.1 and 5/3 = 1.7 to 2.5 grain. To average that out, i’m assuming i cannot vary case weight by more than 2 grains in the same box of ammo. I usually aim for 1.0, sorted into groups if 5 that are 0.1 gn different. Probably overkill, but it helps my confidence! The placeabo effect is very real! ?

You will have to run your own experiment since this is a 30” barrel on a target / bench rifle, which is probably not typical for this community. Would be very interested to see similar results for short barrel 6.5 Creedmoor rifles, as i intend to build an 18” rifle in that caliber.

Hope this helps.

[Edit: How much to back off on powder charge if you switch to heavy cases requires another experiment: Determine effect of powder charge on speed, for your bullet jump/jam, weight, primer and powder combo).]

As always, YMMV. Hope this helps!

NH
 
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wow! Thanks for the write up. I too have found Hornady to have excessive swings from one piece of brass to another. I went to Norma which is much better, then went to Alpha LRP brass which in my opinion is the cats ass. If you get a chance to score some Alpha it would be interesting to read your findings.
I dropped my Alpha powder charges by 1.0 grains to duplicate my Norma loads, which were 0.7 grains less than Hornady brass. So Alpha loads are 1.7 grains less than Hornady to achieve the same velocity.
 
Amazing attention to detail and excellent write up. Thanks. I have always weight sorted brass into groups of 5 when ladder testing and load developing, now I know how much it actually helps.
 
Amazing attention to detail and excellent write up. Thanks. I have always weight sorted brass into groups of 5 when ladder testing and load developing, now I know how much it actually helps.

Thanks for the kind words Brent.

Below is the graph of case volume (y-axis) vs. case weight (in gn) after decapping, case trimming and neck turning. All 5 are Hornady cases. Case volume is in units of “grains of alcohol”. Partial data set.

04933C9C-8DC4-4200-81F8-AE8E1984A87C.jpeg


Surprisingly good (linear) relationship. [Have tried this before with plain tap water and it did not look this good. Guessing it has something to do with water not always getting into the space inside of the flash hole and primer. Some issues with minuscus errors too.]
 
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D97C417B-D226-4B4D-BE18-D7A60CE467E3.jpeg


Muzzle velocity (y-axis) from a 30” barrel (in fps) vs case weight (x-axis) in grain, for FL sized brass, 140 gn ELD-M Hornady bullet, 40.00 grains of H4350. Labradar velocity measurement. Multiple different brands of brass.

This experiment gave the best fit (96%). Slope of the best fit straight line is 2.2 indicating that each additional grain of case weight adds 2.2 fps in muzzle velocity. So if you want your SD below 10, assume case weight contributes 50% to the total, and keep case weight variation below 5/2.2 = 2.3 gn.

At lower speed range, the case weight variations have a bigger impact (3.1 fps/gn), and the result is then 5/3.1=1.6 gn (max allowed variation in case weight).

It might sound like a higher speed range is a better idea, and that is true but only up to a point. Some amount above 2800 fps, the relationship collapsed completely, and very large speed variations (20-50 fps) were observed for cases of very similar weight. The equivalent SD increased from 5.5 fps to >18 fps. Pressure signs started to appear. Advice: Stick to the second highest node if you can, it is often wider, cases and barrels last longer, and the benefit in terms of hit percentage is only 1-2%. [If you compete, and you are in the top 5, you probably do want that last 2%!]
 
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Thanks for the kind words Brent.

[Have tried this before with plain tap water and it did not look this good. Guessing it has something to do with water not always getting into the space inside of the flash hole and primer. Some issues with minuscus errors too.]

Read something recently where an improved way was proposed for measuring case volume: Decap the case, then turn around the empty fired primer cup and reinsert the wrong way. That ensures that any volume differences inside the fired primer cup will not play a role.

Should improve accuracy a little bit. [The result obtained above was pretty good already. Numbers will just be a little different.]
 
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wow! Thanks for the write up. I too have found Hornady to have excessive swings from one piece of brass to another. I went to Norma which is much better, then went to Alpha LRP brass which in my opinion is the cats ass. If you get a chance to score some Alpha it would be interesting to read your findings.
I dropped my Alpha powder charges by 1.0 grains to duplicate my Norma loads, which were 0.7 grains less than Hornady brass. So Alpha loads are 1.7 grains less than Hornady to achieve the same velocity.

Alpha brass (small rifle primer) arrived. Wow! Best packaged brass i ever ordered, in a super solid ammo case holding 100 that i intend to use all the time now. Neat!

Will weight sort and report later on.
 
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wow! Thanks for the write up. I too have found Hornady to have excessive swings from one piece of brass to another. I went to Norma which is much better, then went to Alpha LRP brass which in my opinion is the cats ass. If you get a chance to score some Alpha it would be interesting to read your findings.
I dropped my Alpha powder charges by 1.0 grains to duplicate my Norma loads, which were 0.7 grains less than Hornady brass. So Alpha loads are 1.7 grains less than Hornady to achieve the same velocity.

Alpha brass is superb:
- Weight variation is 0.6 grain over a batch of 100. Slightly better than two batches of Lapua that gave superb accuracy before (weight sorted the entire batch).

- case length was very nearly exactly minimum SAAMI trim length: 1.910” (+- 1.5 thou).

- neck wall variation was very good but not perfect, typically 0.3 to 0.5 thou. Worst case was 0.8 thou. About the same as Lapua. [Will not neck turn this batch and see how it shoots.]

- concentricity was typically 0.3 to 0.5 thou via Sinclair tool. Worst case was 1.0 thou. About the same as Lapua.

- Primer pockets are tighter than new Lapua brass, and hard to seat. Will see how it holds up.

- necks are in the 14.2 to 14.9 thou range, vast majority are 14.2 to 14.5 thou via Mitotoyo ball micrometer.

- case head to shoulder datum line is 9 thou shorter than a fire formed case (Shilen Match Select barrel chambered via a standard SAAMI reamer, pretty sure it is on spec). This is 2-2.5 thou smaller/shorter than virgin Lapua brass. This is a bit of a concern. Planning to load bullets with a hard jam for initial fire forming to keep the case pressed hard against the bolt face to prevent case stretch near the base. Will know more by Sunday. Any advice if this is ok?

- one negative is that the case neck needs quite a bit of deburring. More than normal. Not difficult, just something to note.

- primer pockets are clean and square, same exact depth. No need to mess with them. Tighter than other virgin brass (by about 1 thou).

- flash holes are perfect, no burrs to remove. Do not plan to mess with them.

- i ordered small rifle primer cases. Should last longer.

Can anybody that acquired Alpha brass perhaps report on nr of reloads before discarding? What was the cause?

In short, very little prep to do other than neck deburring and chamfering. [May later change my mind and neck turn them, but trying to avoid that for now.]

Superb brass. And made in the USA. Sells out quickly though.

IMHO: LAPUA HAS MET THEIR MATCH!
 
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Now on second firing of the Alpha 6.5CM brass: Primer pockets are still super tight, too tight in fact, was too difficult to seat Federal GMM primers, reamed the primer pockets with the Lee tool. About 1.5 thou wider now, and 2-3 thou deeper. Primers were flush with the case head, wanted them slightly deeper for safety reasons.

Got superb results: SD=8.0 via Labradar. Good enough for me.

According to the model above (not yet recalibrated for Alpha brass), the 0.6 gn case weight variation in my weight sorted batch of 50 contributed between 1.2 fps and 1.8 fps to the SD. Let’s make that a worst case 2.0 fps. So around 6 fps of the speed variation has to be blamed on a combo of these: Powder inconsistency, concentricity, bullet weight and bearing surface variations, barrel fouling getting better or worse, humidity effects (loading the first catridge to loading the last one took 2 hours to complete, too many interruptions, which allows the fresh batch of powder to suck up moisture and the kernels to swell a little changing the free volume remaining in the case), barrel temperature, and ambient temperature changes between 4 pm and 5 pm affecting powder and primer burn rate.
 
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Excellent write up. Coming from a background in Manufacturing quality control and statistics I appreciate the work that went into this. I feel this is often missing in write ups. Keep up the good work and keep us posted as you continue this.

Quality components require less prep work than cheap stuffs.
 
Quality components require less prep work than cheap stuffs.

Agree with your comment about quality components: Nosler, Lapua and Alpha brass will only benefit 2-3 fps in terms of SD reduction from weight sorting. I still do it (OCD!) and serialize the brass, but mostly for other reasons: if a specific piece of brass end up with poor concentricity (>3.5 thou) three times in a row, i. e. a banana shaped piece of brass has formed, then i will cull it.
 
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Update on Alpha brass:

6.5 Creedmoor ammo built from Alpha brass (before neck turning), using Berger 140 Hybrids, and H4350 produced SDs in the 6-9 fps range. Speed was very similar to Lapua ammo. An SD below 10 is adequate for 600 yard ammo. But lower is always better. Five shot groups at 100 yards were averaging around 0.6”. Best result was 0.35”.

New cases arrived in pristine condition, with no dents, due to superb packaging (a solid plastic ammo case, will use it). Nice!

Still had to do chamfering and deburring. In this respect, Nosler match brass is slighter ‘better’ as they do it for you (and charge you a 2x premium over Hornady brass). But not a big deal, has to do the same for Lapua brass anyway.

I was hoping to avoid neck turning, but gave up on that idea: I measured neck thickness a second time post fire forming, using a Mitotoyo micrometer, and it varied between 14.0 and 15.1 thou over the entire batch of 50. A delta of 1.1 thou is not too bad, but not great either. Typical Lapua brass in my experience varies about 0.5 to 0.6 thou. So I decided to neck turn the Alpha brass down to 14.5 thou, bringing neck thickness variation down to under 0.5 thou. About 50% of the neck area is cut, so just the high spots are removed. I was hoping to avoid this, but the bullet concentricity results were in the 1.5 thou to 5.5 thou range, not what i would consider adequate for 1000 yard ammo (prefer worst example to be below 2.5 thou, with an average closer to 1.5 thou).

After neck turning, the brass was loaded again, and shot at paper targets at 50 yards. Ammo worked pretty well, and produced an average group size of around 0.55 MOA. Good enough for me, even though i have seen better in the past (my prior barrel was better).

Measured runout again post firing (after neck turning) and it improved to 0.5 thou to 2.5 thou, with only two rounds out of 50 at 3.5 thou, and these two were put aside. Likely an operator error.

Also, primer pockets were a tad too shallow: seated with Federal SRP match primers, they were either flush with the case head, or just barely below the head. Would not feel comfortable dropping such a loaded round on a hard surface. Used the Lyman case prep center to correct the primer pockets, and the primers are now 10 thou below the head. Primer pocket diameter was also slightly less than virgin Lapua brass and primers were uncomfortably hard to seat. This was a concern. The primer pocket reaming cured that problem as well. A different brand of primer likely would have been a perfect fit. Some folks switch to different (1 thou larger) primers once the brass has been reloader say 15 times. That might buy you another 5-7 reloads. Or not!

Will test the third reload soon and report back. So far the Alpha brass shoots well and results are mostly on par with Lapua. Will need to wait and see if they last as long as Lapua SRP brass (now at 16 firings and holding up very well). Time will tell.

In summary: Good quality brass with a very tight weight range, with no need to weight sort. In this respect, better than Lapua. [Of course, you can buy 500 new Lapua cases and weight sort them to get a box of 50 cases that is just as consistent, but at a significant cost.]

Neck wall thickness variation (around 1 thou) could be better. Adequate but not stellar. Lapua wins here. If you compete, then neck turning is probably recommended.

Primer pockets needed a minor amount of work. Lapua has always been perfect here. Not a big deal. Also see workaround below.

Flash holes were checked and appeared to be perfect. Good.

Often out of stock, and hard to find. Must be gaining popularity...

Could reuse the same load recipe from my prior Lapua based ammo, without any pressure signs, and speed was very similar. That is useful. Less load development work. Note that others have reported significant volume differences between Hornady and Alpha brass, and the same load recipe will likely not be safe. As always: Start low and work your way up. Even if you change “just” one component - like brass or primer.

Stood up well to my H4350 ‘max’ load, and no ejector marks were found. Case volume appears to be similar to Lapua. [Your batch of brass may be different, so always double check by starting low and working up.]

I can see why people recommend Alpha brass, given the narrow weight range. But anything better than a 1 grain weight range improvement is not really worth it. At worst, that will add 2 fps to your standard deviation. See above. Even a 2 gn case weight range would still be adequate (<4 fps increase in SD). Alpha brass is perhaps better than it needs to be in this respect. A case of diminishing returns…

IMHO Alpha Munitions has some improvements to make to truly beat Lapua: More consistent case neck thickness and correctly sized primer pockets would be my two main complaints.

I would love to see them take on Lapua and create real competition for the meticulous engineers from Finland. Maybe the Lapua prices will come down if a cheaper alternative becomes established... but probably unlikely. People buy based on brand, and it takes time to build up a new brand. But it sure would be good to have alternatives!

Will report accuracy results for the modified Alpha cases when i get a chance to visit the range again. Expect it to be slightly better, but we shall see. Hope this helps.

Late Addition: Buddy of mine sent the info below, not sure how accurate, but it might be helpful if you need to pick a primer that will fit the tight Alpha brass as-is (no primer pocket reamer needed). Also, once the primer pockets have expanded, you may want to pick a different primer with a slightly larger diameter. Let us all know how this works out for you!


5BAFBCBD-F13A-4E2B-B695-55D3B85A3952.png
 
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Great write up.
There will still be those resistant to sorting brass to remove the light or heavy one or two (or three).
Many believe virgin brass shoots just a little different than once fired, but don't believe case weight matters.
Go figure.
I've found that the reverse fired primer helps. I bet you just throw them away :)
When using water, one drop of dish soap per cup reduces surface tension and does not affect density enough to notice.
You can also wick with a cotton swap to get a flat liquid surface.

Again, great effort.
 
Minor update on Alpha brass: Case weight and case volume was measured, and results were superb. Easy to get 50 cases with less than a 0.6 grain weight range. Cases are quite heavy and necks are thicker (originally necks were between 13.8 thou and 15.2 thou, neck turned them all down to 14.0 thou). Only downside i found was that if you load lower (jammed the bullets, an experiment, and dealing with summer temps in the 90’s), so i need to load 1.2 grains lower, the neck does not always seal off the chamber and i get 3-4 mildly sooty cases per batch of 50. No primer leaks, it is clearly from the neck not sealing. Speed for these rounds were normal, but they did not extract normally. Had to close the bolt again and open again, then they jumped out. Did not happen at higher loads (near max). Intend to neck turn them down to 12.5 thou and try again!

Good brass, but perhaps thick necks are in general not compatible with lower powder charges?? Never seen this issue on Lapua, Nosler, Norma or Hornady brass before (might have missed it), and during load development i tend to start 3 grains below book max, but they were all 12-13 thou necks (all neck turned). Ever seen this?

(Btw: Annealed every time on an AMP machine. So i don’t think the necks are overly hard.)
 
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A bit of a late reply, but thank you VERY MUCH NamibHunter for all the great information you provided here. This does indeed save some time for all of us starting to compete and wondering where things matter. I am going through the process of figuring out just how to sort my brass. Batched rather tight on runout (<= 0.0005, <=0.001, <=0.0015, and <=0.003 (these go in the AR, not my bolt rifle). Perhaps I am a little too tight here :). Then I went on to weight and noticed the Hornady brass has huge swings (low to high on 300 is about 17gr). Finding this article greatly helps in my batching of cases by weight knowing what weight/velocity changes are expected. Thanks again!
 
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Thank you for your painstaking work to test and document the relation of case weight to velocity and thank you for sharing your information. I'm about to start reloading old Prime (RUAG) brass after thousands of rounds of Hornady brass reloads and your info will help me adjust and test my initial loads and speed up my load development.
 
That was incredibly helpful....thank you for sharing

You are most welcome sir!

The graph was developed mainly to determine how wide the weight range should be, given your personal goals for SD and ES. A 100 yard BR competitor or an ELR competitor might pick 1 fps, while an F-class competitor might be happy with 2 or 3 fps, and a steel plinker will likely choose 5-8 fps and save money by avoiding the expensive brands of brass. Hunters who limit themselves to 400 yards or less probably don’t need better than 10 fps.

I have not yet used the graph for modifying a load recipe when changing from say Lapua to Alpha brass, but plan to try it soon. The aim would be staying inside the same node as before, so trying to get the same/similar speed as before. Would be interested in your feedback on how well that has worked for you. The fact that my chamber could be smaller or larger than yours by a few percent (and the fact that the relationship flattens out as you approach max pressure) might well have an effect, but it should provide a good starting point.

Stay safe!
 
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I've not yet begun to reload the 6.5 Cr as i've only recently purchased a new barrel in this new for me caliber. That said your preliminary data has already helped me decide on which cases to procure.

Ultimately it would be very interesting and valuable if a relationship factor could be established to facilitate translation between cartridge case brands/makes.....but that's asking a lot and perhaps too much.
 
Have you tried Peterson brass? I am shooting Lapua and Alpha and found the Peterson brass to be extremely similar, if not more, consistent.

I have ordered a box of shiny new Peterson brass, and they are sitting on the shelf waiting for their turn. Have read very good reports about Peterson.

Will report back when i get around to testing it.
 
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For those with a statistical bent, my results indicate that there is significant “non-linearity” at the top end. [Not a perfect straight line as you approach max pressure, some curvature to it.] I’m guessing a bit of experimentation could yield a better equation. Future work perhaps. If you are interested in a collaboration, PM me.
 
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I’m very interested in developing the idea that one could make a formula to correlate a load recipe with same powder, primer, bullet to different brass if one knew the difference in case capacity.
 
@NamibHunter

Thanks for your commitment, I highly appreciate your sharing.

Your experiences have now reached the South of Germany.
(y):)
 
@NamibHunter

Thanks for your commitment, I highly appreciate your sharing.

Your experiences have now reached the South of Germany.
(y):)

Happy to be of service. My Germanic forefathers will be pleased. 😊

I never lived in Germany on a permanent basis, but did consulting work in Bavaria for several years, mostly around Ingolstadt. Loved it!
 
Audi?

Well, I´m from the South-West, Baden not Bavaria, near to Freiburg at the rims of the Black Forest.
Just a jump to France (Alsace) and Switzerland (Basel).

Where did your anchestors come from?

And if you want, you can PM me your German family name, onomastics is a hobby from me.
:)

Maybe your name has a special meaning, mostly it gives an indication of what your forefathers´ profession was (Smith, ...), where they lived, what body measures they had (Little, ...) etc..
Sometimes the names changed over the centuries and are only somewhat alike what there meaning was in the middle-age, or they are very seldom, or they show a line of earlier knights or lords.

Yeah, I know ....
:cool: :sneaky:
 
Just an update: Got hold of the Sinclair primer plugs and measured case volume for 20 fire formed Lapua SRP cases (trimmed to spec), and the linear / straight line relationship between case weight and case volume was clearly visible. No outliers were found.

Just an aside: It is challenging to accurately measure water weight as the meniscus (the surface shape of the liquid) is hard to get the exact same every time, but it is very easy to measure case weight accurately on an FX120. There might also be trapped air in the flash hole. I used a mixture of water and alchohol.

Of course, checking 20 cases and not finding an outlier does not prove that there are none in a batch of 1000. Poorly made brass can have a thicker web, but experience shows that premium brass rarely has this problem. Would still recommend that you mark cases that produce large ES twice in a row and simply cull them. Whether that was due to bad neck tension (different metallurgy perhaps) or case volume differences does not matter, just chuck it out.

Also i serialize my brass so each one has a unique number engraved on the web area (yep perhaps i am ever so slightly OCD...), but that makes it a lot easier. Hope this is helpful.
 
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Lots of great info. Thanks @NamibHunter !

My biggest complaint about the Alpha has been the volume (and therefore speed capability). While I’ve run my Hornady as hot as 43.8gr, even 41.5gr in the Alpha is compressed and already showing a tight bolt lift. If I was willing to lose around 100fps, it would be amazing brass.
 
Lots of great info. Thanks @NamibHunter !

My biggest complaint about the Alpha has been the volume (and therefore speed capability). While I’ve run my Hornady as hot as 43.8gr, even 41.5gr in the Alpha is compressed and already showing a tight bolt lift. If I was willing to lose around 100fps, it would be amazing brass.

Fair point: If you found your node / speed flat spot 50-100 fps lower than max (my situation), then Alpha brass works fine, you just load less powder and adjust the load to get the same speed as you had before with your prior brand of brass. Of course, if you use thin skinned brass like Hornady and load close to max, then yes you are going to lose speed.

Btw: The best accuracy improvement i ever got at 600 was not buying some high tech equipment, but moving from Hornady brass to Lapua.
 
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