PRIMER CHOICE

There are a few questions.

Are small primers more accurate than large primers? 

Does firing pin strike force variation vary accuracy?
We have the report of Charlie Dell’s test, saying NO. Stevens 44 1/2 rifles, I’m told, have adjustable firing pin force. Testing is simple.

Does primer choice affect accuracy?
My experience and testing says NO, that either the primer sets off the powder charge, or it doesn’t. If the gun fires, accuracy does not vary with primer choice.

My test results for primer choice with cast and jacketed bullets are not satisfactory, other variables are included and/or sample sizes are too small.

A search of the internet found no reports of reasonable tests. There are reports about brisance and primer energy and cup dimensions and anvil location; but the reports that I found connecting primer choice and accuracy have distressingly small sample sizes.

One of the reports counts primer choice in loads recommended by competent shooters. This seems to be a reasonable though fuzzy way to look at the question, so I did.

CBA NM primer choice, by place, (1 = first, 2 = second,…).

A rifles precision is derived from the correct combination of several components coming together as a successfuly completed unit. Accuracy is soley derived by individual shooter abilities. Where one places in a match is determined by both precision and accuracy. Powder choice can determine the correct primer choice. Example Ball Powders are harder to ignite and the wrong primer choice will leave unburnt powder in the barrel. Unburnt powder can directly effect a rifles precision as can all of the individual components one chooses to use.

A Sharps will still go bang with a broke firing pin but accuracy will suffer greatly. Had the same thing happen with my C-sharps 85.

There is no magic formula. For any primer, any bullet, any powder, any rifle, and let's not forget, any loader/shooter there will be certain combinations that work better than others. That said, it becomes fairly common knowledge that a few certain powders require a certain level of primer to work as well as they can.

Totally agree Ken and as BobZ noted here or in another thread there was a batch of the White Box Winchester Large Rifle primers that far exceeded anything then or since for my use.

Schuetzendave, your targets really could almost prove the point of sorting primers had you weighed them, or not.

Target #2 has a random high flyer, target #4 has vertical string. Both if caused by velocity, would be somewhere around 10 fps. 

If targets 1,3,5 had matching primers, it would be a good indication, but those three targets are almost too good to get any useful information, other than to rule out shooter error on targets 1&2. 

Maybe a longer distance shot, more of a pattern could be seen?

There has been more and more discussion in the last few years in the long range crowd and group sizes are shrinking.

Here's one persons target at 600 yards with primer weights listed and a link to the thread.

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Why is it that people that cast and sort bullets to a 1/10 of a grain, powder to 1/100 of a grain have trouble thinking that sorting primer charges(because that's really what you are doing) might make a difference?

For a disclaimer, I probably don't shoot consistently  enough to have my targets have much meaning compared to yours. What I can say is that I shoot a reasonable amount of different disciplines, reasonably well. The resistance of one style of shooting to accept a different idea from another, seems to be the only universal truth.

I am a ways from likely being able to see the difference sorting primers can make, doesn't mean I can't learn something now about quality control and if it might matter.

Dave, What did you shoot in the  International Benchrest Championships?

The following data was originally posted on Sigforum.  It shows that for a revolver cartridge, the .327 Federal, the choice of primer is critical.

I have a Ruger Single Seven in .327 Federal with the 7.5" barrel. I have found that loading the .327 Federal presents some challenges, namely dealing with large extreme velocity spreads, 150-200 fps.

Brian Pearce wrote an article about the .327 Federal in Handloader magazine, issue 294 (Feb-Mar 2015) and answered some questions I asked in issue 312 (Feb-Mar 2018) about reloading issues with the 327.

Based on his comments regarding primer testing I decided to run some comparisons of a variety of small pistol and rifle primers in the .327 Fed.

The load was 11.0 gr 2400, in Starline brass. Bullet was the Hornady 100 gr XTP. Cases were trimmed to the same length, primer pockets and flash holes uniformed, and a firm roll crimp was used.

I compared 10 different primers. Fifteen shots were fired with each primer. Velocity was measured 15 feet from the muzzle.

CCI 500
Velocity: 1451 fps
Extreme Spread: 179 fps
Standard Deviation: 60.1 fps

Federal 100
Velocity: 1379 fps
Extreme Spread: 74 fps
Standard Deviation: 20.3 fps

Federal 200
Velocity: 1352 fps
Extreme Spread: 74 fps
Standard Deviation: 21.2 fps

CCI 550
Velocity: 1443 fps
Extreme Spread: 163 fps
Standard Deviation: 56.0 fps

Federal 205M
Velocity: 1360 fps
Extreme Spread: 50 fps
Standard Deviation: 18.0 fps

Winchester WSP
Velocity: 1357 fps
Extreme Spread: 44 fps
Standard Deviation: 13.7 fps

Winchester WSR
Velocity: 1360 fps
Extreme Spread: 69 fps
Standard Deviation: 21.9 fps

CCI 400
Velocity: 1365 fps
Extreme Spread: 138 fps
Standard Deviation: 33.5 fps

CCI 450
Velocity: 1455 fps
Extreme Spread: 73 fps
Standard Deviation: 19.6 fps

CCI #41
Velocity: 1370 fps
Extreme Spread: 140 fps
Standard Deviation: 37.5 fps

Of all of these, the second to the last one, with the CCI450 gave the best results, giving the highest average velocity, with the lowest pressure signs, as determined by primer appearance and ease of case extraction along with good accuracy. One other thing I had noticed - the muzzle blast and flash often varied a lot among the same load, with some giving a much louder report and large flash, with others being not as loud and little flash. The quieter less flashy loads gave the highest velocities. All 15 of the rounds with the CCI 450 primer were like this, no big blast or flash.

The Federal 205M and Winchester WSP gave similar results.