Rifle Primers - Large or small?

EddieCoyle

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There's an article in the latest Shooting Illustrated comparing the accuracy/consistency/precision of large primers vs. small in cartridges where you can get brass with either a large or small primer pocket.

Here it is:
Large- or Small-Rifle Primers: Which is Better?

The author did his testing with a wildcat cartridge of his own creation. His half-assed test gave a slight advantage to the rounds loaded with large primers. This is the opposite of what I've seen.

I load three rifle calibers that are available with both small and large primer pockets (6.5 Creedmoor, 6.8 SPC, and .308) and have found the small primer versions to be better in every case, especially with the 6.8 SPC.

What have you all found?
 
I've not seen .308 with small primers but all my .308 ammo is milsurp ball and tracer except for a couple of boxes of lead tipped hunting ammo.

Is the small primer .308 strictly a commercial product?
 
Don't have a dog in this fight, but I laughed at testing something using a wildcat and trying to use what is by definition anecdotal evidence to assess a larger conclusion.

Not to mention his tiny sample set!
 
I know for a fact that small rifle primers will shoot generally better than large in 6.5creed. Channel on YouTube did a video about it, called Johnny’s reloading bench. There’s also a reason why lapua makes 308 Palma brass with small primers
 
I’m very happy with my small rifle primers in 6.5 creedmoor. I have no way to compare the 2 fairly as I only own SRP brass. My reloads shoot better than any factory ammo I’ve tried. I guess I have done well with my brass prep so far as my Lapua gave me an SD of 3 with a sample size 15 shots using Magneetospeed.
 
7.62x39 can be large or small. I haven't tried dialing in the most accurate round in that yet but it's on the list of things to get to.
There was a rumor many years ago, perhaps from Pedersen's Rifle Shooter or Gun Digest, that small primers had an inherently more consistent ignition than large primers and small standard primers were more consistent than small magnum primers. I will likely never remember where exactly I heard that, though.
 
Here's my crackpot theory.

Primers all have manufacturing variance. Let's assume for sake of argument that the amount of priming compound in the primer can vary by as much as 2%.

In a smaller primer, this 2% variance has a smaller absolute effect on the amount of priming compound in the primer since there is less compound to begin with.

Therefore, the variance in how much "kaboom" the small primer has is smaller, and thus the effect on accuracy is smaller.

This concludes my crackpot theory.
 
Maybe I'll try to track down some small primer brass 308 for some comparison testing; I've only seen the large kind.
Interesting stuff, though.
 
I wonder if this applies to pistol calibers as well? Might be worth investigating for bullseye shooters, especially in 45 ACP.

But it might mean that those mutant small primer brass cases actually have a good use.:(
 
I wonder if this applies to pistol calibers as well? Might be worth investigating for bullseye shooters, especially in 45 ACP.

But it might mean that those mutant small primer brass cases actually have a good use.:(

I feel like there would be some mitigating returns in that case, but I am not a bullseye shooter either.
 
I wonder if this applies to pistol calibers as well? Might be worth investigating for bullseye shooters, especially in 45 ACP.

But it might mean that those mutant small primer brass cases actually have a good use.:(

You'd have to be a better shot than me. It might improve groups by a 1/4 MOA.
 
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