What influences ES/SD the most?

.1 - .2 grains on a load in the 30s of grains could make some difference. That's a pretty big spread - in my smaller powders, I hit the mark exactly on a .02 increment scale. Powder charge is one of the elements that's most in our ability to control, so why not do so?

I've found that neck tension variance does play a role. I documented it in a thread where I was documenting the differences when using a mandrel and neck lube:


On the shoulder, more movement means more opportunity for error. Consistency obviously matters here too.

When loading my 6GT, primers played a huge role. CCI400(regular) loads were 3 times higher ES/SD compared to CCI450(magnum) loads. I tested the 2 primers many different times and every time was the same results.
Jim

Inside flash hole. I found raw VS deburred had a huge influence on ES/SD. Lapua doesnt have much at all (drilled flash holes) and have not tried peterson, but hear its excellent.

The usual suspects are hornady, winchester, federal, S&B, norma to some extent, starline, etc..

I will add that I proved to myself also that how you actually shoot believe it or not matters a lot. For example if you shoot one shot with your shoulder pressed firmly into the stock and the next shot you allow more movement of the rifle... it definitely has an effect.

Your question doesn't really have one answer as many factors affect velocity and any one may have the greatest effect. If you look at the entire process you have many things going on that interact. First is ignition and combustion. The primers needs to be consistent and the powder column needs to be consistent at the time of ignition. In some cases the powder will burn differently if charge shape is different. This is likely to happen if the case is not close to full. Because the burn rate is a function of pressure the point on the pressure curve where the bullet releases is important so neck tension is going to affect the burn rate and peak pressure and ultimate velocity. Different case sizing between charges will affect the energy absorbed in expanding the brass hence different energy available to the bullet. Obviously charge uniformity is important but if you consider a 0.1 gr variation in 223 that is on the order of 12 fps but in a 308 it is about 6 fps and in a 30-378 Weatherby its 3 fps.

The bottom line is having a realistic exception for SD for your needs, pay attention to the your loading and strive to maintain consistency. There is also one overriding thing to remember, SD and ES are test numbers and while they have importance the goal is bullet on target. Don't lose track of that fact.

For powders that are temperature sensitive, the timing of when you chamber a round and how long it's chambered before you press the trigger can be part of the ES. Imagine firing a 5 shot group while monitoring the temperature of the chamber. Shooting that group in 1 minute versus 5 minutes will impact the temperature profile. So if you shoot rounds 1 through 4 within 15 seconds of chambering the round, the later rounds will get heated more due to to the rising temperature of the chamber. But if you chamber, then delay shooting round 5 after 4 relatively quick shots, round 5 will get much hotter.

Depending on the powder and the cartridge used, the impact of 0.1 to 0.2 grains is partly determined by where you are at in terms of approaching pressure limits. A plot of MV versus charge is not a straight line.

iceng said:

Inside flash hole. I found raw VS deburred had a huge influence on ES/SD. Lapua doesnt have much at all (drilled flash holes) and have not tried peterson, but hear its excellent.

The usual suspects are hornady, winchester, federal, S&B, norma to some extent, starline, etc..

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Lapua does not have drilled flash holes. The worst flash hole burs I have seen were actually in some gold box 243 brass.

Here is some Starline 6 Creedmoor random chosen charge weight, 1st and 2nd firing, not annealed in-between. Run on a chargemaster, charges not confirmed for weight, sized with standard hornday FL dies, with expander ball. brass not sorted flash holes not de-burred.

To answer one of the OP question. .1 gn variation ( +/- .05 gn ) assuming 3000 fps on the 30 gn load = 3000/30 * .1 = 10 fps contribution. .2=20 etc. I weigh and sort my cases to 1 gn total spread, weigh my charges to +/- .02 on my 6x47L and my SD is usually around 5-7 for my match load. And loads of case prep.

My SD never was consistent till i got a better scale that got me to .02 resolution

David

TripleBull said:

For powders that are temperature sensitive, the timing of when you chamber a round and how long it's chambered before you press the trigger can be part of the ES. Imagine firing a 5 shot group while monitoring the temperature of the chamber. Shooting that group in 1 minute versus 5 minutes will impact the temperature profile. So if you shoot rounds 1 through 4 within 15 seconds of chambering the round, the later rounds will get heated more due to to the rising temperature of the chamber. But if you chamber, then delay shooting round 5 after 4 relatively quick shots, round 5 will get much hotter.

Depending on the powder and the cartridge used, the impact of 0.1 to 0.2 grains is partly determined by where you are at in terms of approaching pressure limits. A plot of MV versus charge is not a straight line.

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Good point. Also how the ammunition is handled once on range can have an effect, especially if you shooting position is in the sun. Ball/Spherical powders are usually more sensitive to this than extruded but all powders are temperature sensitive to some extent.

As for linearity of the charge/MV it is true that it is not linear but is close to linear for typical loading ranges.

alamo5000 said:

View attachment 7948726

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Nice chart. From where? What Cartridge?

Dstoenner said:

My SD never was consistent till i got a better scale that got me to .02 resolution

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Charge weight! Accuracy versus precision! The accuracy of the charge weight is not the critical item but precision is. Having a scale that consistently gives the same charge weight for the same charge is the goal. Weighing a tenth off every time is not material when the same scale is used every time. Regardless of the scale, the scale should be re-zeroed (tare) before every charge is thrown. This is good laboratory practice and eliminates the major source of scale error which is drift. Most higher end scale including the Chargemaster and the the Fx-120i have this automatically.

Jefe's Dope said:

Is it linear?

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If you mean is the test data linear and all points lie on a straight line then the answer is no. With enough test data and enough test runs it would approach a good fit to a straight line. You have to remember that each shot is subject to all of the variables we've discussed plus some.

Debating this is a waste of time and space. The combustion efficiency is a function of pressure and introduces a bit of non-linearity but that effect is quite small.

When you are considering a point along the curve that is not changing that much it is pretty linear. And this is for approximations of how much contribution this one variable makes in the over all final value of SD as measured by your chronometer.

In engineering and math for a given problem you try to quantize variables. Figure out the biggest contributor. Solve or minimize it. Then move to the next. Oh and by the way even the chronometer has its limits. Lets say it is .1% accurate + 1 digit (probably close). .1% of 3000 fps is +/- 3 fps. Plus 1 digit makes it 4 fps. That is if every other variable is perfectly 0!!

Another factor in statistics is how many samples. IIRC a sample of 5 shots will more than double when you do at least 20 shots. Brian Litz has a table about that.

supercorndogs said:

Lapua does not have drilled flash holes. The worst flash hole burs I have seen were actually in some gold box 243 brass.

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I agree, but for me it was gold box .308 and .338LM and they were bad.

Chris

Doom said:

Charge weight! Accuracy versus precision! The accuracy of the charge weight is not the critical item but precision is. Having a scale that consistently gives the same charge weight for the same charge is the goal. Weighing a tenth off every time is not material when the same scale is used every time. Regardless of the scale, the scale should be re-zeroed (tare) before every charge is thrown. This is good laboratory practice and eliminates the major source of scale error which is drift. Most higher end scale including the Chargemaster and the the Fx-120i have this automatically.

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I agree with your hypothesis but I disagree with your perception of charge weight accuracy vs precission.

Accuracy is how close it can get to the real value weight. Precision is how close the next charge is to the previous charge. If the scale is +/- .1 gn + 1 digit (normal defined accuracy) you cannot get precision better than that accuracy. You have to have high accuracy for high precision. That is why everybody is moving to force restoration scales that go to +/- .01 gn or better.

And yes I "tare" my scales every 5th charge or if I think something is wrong even sooner. Like I said when I got better accuracy, my precision of charges was better and my SD's got smaller accordingly. Could they get better if I got a better scale yes but quite honestly, I have good enough to know my problem now is not my ammo but my wind call. My elevation at 1000 yards on my shots are within the 10 ring but the wind just keep blowing out to the 9 ring often enough to keep me humble.

Doom said:

Nice chart. From where? What Cartridge?

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Look in the bottom right hand corner in small print.

I didn't grab which cartridge. But the take away is brass, assuming your charge weights are all equal.

Case neck/shoulder hardness.

powder ignition from round to round .

Dstoenner said:

Accuracy is how close it can get to the real value weight. Precision is how close the next charge is to the previous charge. If the scale is +/- .1 gn + 1 digit (normal defined accuracy) you cannot get precision better than that accuracy. You have to have high accuracy for high precision. That is why everybody is moving to force restoration scales that go to +/- .01 gn or better.

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I agree with your definition of accuracy. And I used an incorrect term. I was actually referring to bias error, which if consistent is not an issue when it is consistent from one loading session to another. However you are incorrect in that it is possible to have high precision with without high accuracy. Drop your brass calibration weight on a concrete floor and then use it for calibration and you will have an accuracy problem in all likelihood because you 50 gram weight will likely not long weigh 50 grams but your precision will be the same.

As much as I hate getting into it, accuracy is often a misused term. It is often used in specifications but is seldom defined as to the basis on which it is based. ISO recognized this when developing many of the ISO specifications and uses the following definition:
"ISO 5725 uses two terms "trueness" and "precision" to describe the accuracy of a measurement method. "Trueness" refers to the closeness of agreement between the arithmetic mean of a large number of test results and the true or accepted reference value. "Precision" refers to the closeness of agreement between test results."

Anyone still using a triple beam balance? Small sample size but I do my final charge weight adjustment on a old 30 year old balance beam.

Load 1 tested before the chamber, barrel, ammo heated up.




Load 2

Neck tension has had an impact for me with SD/ES.

I believe some variables we can control and some we can’t, we can weigh this, measure that but in the end if our primers have 5-7k psi’s variation, who’s to know the outcome.. you can run the best powders in the world and there will always be a swing… some guys chase their tails looking for the perfect load.. burning up barrels and scarce components.

Dstoenner said:

You have to have high accuracy for high precision.

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You can also call the two terms "bias" and "precision. You can, absolutely, have high precision and poor accuracy. You can also have high accuracy and poor precision.

BCX said:

I believe some variables we can control and some we can’t, we can weigh this, measure that but in the end if our primers have 5-7k psi’s variation, who’s to know the outcome.. you can run the best powders in the world and there will always be a swing… some guys chase their tails looking for the perfect load.. burning up barrels and scarce components.

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What primers do you find give the most consistent SD / ES / pressure? I’ve been using GM215M. I’ve always wondered about them because the last layer (on top of the anvil, I’m told it’s a sealant) is very inconsistent in the lots I have.

These are used in my 300 WM and 300 PRC.

I only use Fed 215 M in my long range rifles. I read a article years ago how primer PSI varies in a box of 100 not a case or lot! Primer PSI variation we can not control to my knowledge!

I use a Amp Mark 2 Annealing machine , mandrel w Hornady one shot.. leave the lube in the neck, has really helped to bring the ES/SD down.

And only use quality components!

So is this red layer actually a sealant that has no effect. This is 50 primers out of the brick I’m currently using. You can see how the 4 at the lower left are only partially filled. The previous brick was much worse, probably 15% were that way. I’ve been sorting them by fill and would like to skip that step if it’s not important.

Edit: … 4 at the lower right ….

I wouldn’t worry about sorting primers. Personally I think uniforming pockets and a consistent seating depth or anvil crush is more important…

Don’t be the guy that sorts primers by measuring and weight sorting primers …

When I over think these things, I sometimes wonder. What if it’s not our reloads, what if it’s the chrono too? Could be a lot of factors. That’s why I stop worrying about it and just see the shots on paper instead.

Jefe's Dope said:

Is it linear?

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is linear, but not from 0 to 30gr, but more from 25gr to 30gr, and this linear line doesnt start at zero/zero.

Jefe's Dope said:

Powder? How much should .1-.2 grains of powder variance change muzzle velocity?

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you have cronograph, you did a ladder test, and you can't calculate this for yourself?

BCX said:

Anyone still using a triple beam balance? Small sample size but I do my final charge weight adjustment on a old 30 year old balance beam.

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yes. i use new from rcbs: m500. accurate as fx-120; i can see a change i 1 kernel of N140, which is ~0.01gr heavy. but not as fast as autotrickler.

Dstoenner said:

My elevation at 1000 yards on my shots are within the 10 ring but the wind just keep blowing out to the 9 ring often enough to keep me humble.

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dont forget that even bullets have variations of their BC value, and that's why everybody are sorting those inconsistent bergers...:

https://thescienceofaccuracy.com/conquer-the-castle-match-elr-radar-testing-report/ (you must register for see it)

MarkyMark007 said:

yes. i use new from rcbs: m500. accurate as fx-120; i can see a change i 1 kernel of N140, which is ~0.01gr heavy. but not as fast as autotrickler.

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I use an almost 40 year old RCBS for final weight check after throwing with a ChargeMaster. Same results, you can see each kernel of H1000. Calibrate it with a weight set and you are good to go.

Bandit320 said:

View attachment 7949074

So is this red layer actually a sealant that has no effect. This is 50 primers out of the brick I’m currently using. You can see how the 4 at the lower left are only partially filled. The previous brick was much worse, probably 15% were that way. I’ve been sorting them by fill and would like to skip that step if it’s not important.

Edit: … 4 at the lower right ….

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It's not sealant, it's just dye to mark them. It looks like they are all filled about the same to me.

Some on here have done extensive primer testing. I have only tested a few and only to see if it effected my speed and POI between Winchester and CCI. There was no difference in what I tested.

I use CCI and I have gotten to where I like the 450's for all SRP accept 223.(I use 400's for that but really just because I have a good amount of 400's and it doesn't seem to matter in 223.

For LRP (for me that's 6.5cm and .308) I use BR2.

MarkyMark007 said:

dont forget that even bullets have variations of their BC value, and that's why everybody are sorting those inconsistent bergers...:

https://thescienceofaccuracy.com/conquer-the-castle-match-elr-radar-testing-report/ (you must register for see it)

Click to expand...

I agree about the BC variation. Actually at 1000 i shoot 115 DTAC’s but i do sort on OAL. That is what Brian Litz says to do in order to even up the BC. At 600 i shoot the 109 LRHT. Berger says they are guaranteed to be within 1% in a box. So I don’t sort those.

David