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Small vs Large primer test: Rifleshooter.com

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Interesting test conducted by Rifleshooer.com to see if there's any difference between small and large primer 6.5 Creedmoor brass. 


In short:

Small primer brass showed an INCREASE in velocity on average over the large primer brass (which seems to contradict other research I'm sure we've all read)

Small primer brass gave smaller groups on average than large primer brass

Large primer brass showed on lower SD between charges on average than small primer brass

**  Caveat, author used Starline brass as it's the only manufacturer to offer 6.5 Creedmoor in both small & large primers. Also he only used two primers, Wolf & CCI450.

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Food for thought, but we're sure Laurie will be along shortly to offer some insight into whether this is a valid observation and if so, why . 

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To gain the benefits of SR priming, you also need the small (1.5mm / 0.059" dia.) flash-hole instead of the standard size (2mm /0.079" dia.). The Starline brass used in the tests has the large flash-hole in both versions. This alone almost certainly accounts for any odd findings on average MVs - the small flash-hole is reckoned to reduce MVs as much as, more likely more, than the primer size.

I looked at this test a long time ago and although don't remember much about it now, do remember being distinctly unimpressed by its methodology and the numbers of cartridges fired.

However, since IMHO there are no internal ballistics / accuracy benefits in using SRP Brass with a large size flash-hole compared to the standard LRP variety, I'd never buy any cases like this. The only potential benefit is that with a smaller pocket, the SRP version might last longer before pockets become slack and the cases have to be scrapped.

There are a few cartridges around where you can get either primer size allied to the 2mm flash-hole - 7.62X39mm and 6.8mm Rem SPC being the two most common. When I had a 6.8 SPC AR-15 straight-pull, I did a side by side test between Remington (LRP) and Hornady (SRP) cases which fortuitously had very similar case capacities as measured using the water overflow method. With this small capacity case and powder charge - a great deal less than those of the Creedmoor, I expected to see the Remington variety produce significantly higher MVs, but there was nothing at all between them, likewise in ES and group sizes. It seems that if the powder is cleanly ignited, it's cleanly ignited when the only difference  is the primer alone.(In the case of the 6.8, it seems Remington made a poor move in going for LRP with this smaller diameter case-head. The best, strongest, and longest lasting brass for the cartridge was Silver State Armory's SRP version when it was produced.)

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Very interesting Laurie.

I too picked up on the fact the small primer brass didn't use the 'true' small diameter flash hole but did think just the difference in primer was more likely to affect things as apposed to the diameter of the flash hole itself. I've learnt something new there.

Strange you say you'd looked at this test a long time ago as it appears the author conducted it (or published it on Rifleshoooter) in May this year. Is this a copy of an older test that was published elsewhere?


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I use Starline 6.5 Creedmoor SRP brass, using Ramshot Hunter as well as Viht N140 & N150 all my velocities were well below (50-80fps) the same loads in LRP cases. 

Of course the Murom KVB-223M primers will also be contributing to it, as previously discussed they give a lower fps reading compared to the same loads using Federal 205's.

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I've found the 1.5mm F/H SRP brass to be significantly down on MVs but also down on SD/ES, one of the reasons I initially came to use it. The outcomes from my own use are the exact opposite of that test although as pointed out, it was conducted using the 2mm flash hole brass.  I am still not sure why a lower energy primer would produce higher MV's though.  

Laurie's opinion is one that I share.  The methodology doesn't seem that thorough, in particular the use of new, unfire-formed brass (I would never conduct serious testing on fresh brass for obvious reasons) and only 10 shots conducted per group.  Multiple 7 shot groups might have been the better bet to draw any meaningful conclusions from, not just one from new and one from fire-formed.  I would place little store in the conclusions.  Only two primer brands were used too, so a meaningful comparison across the board was not witnessed and again. conclusions from just two brands may be overturned with the outcome of multiple primer tests conducted as thoroughly as Laurie's last set of primer tests.  All in all, I thought it a very poor test "glammed up" with the presentation.

As to the superiority of SRP brass in CM, I am undecided about which I'd go to for precision but one thing I do now know and that is that SRP Brass is not worth the extra £40/100 over the LRP variety especially now that there are many quality brands available which outlast the original Hornady 6.5 LRP cases and most like Lapua and Norma with sensible loadings should see double digit loads possible.  For that reason plus the 100fps (or more) handicap using SRP brass, I won't be buying any more when mine eventually gets scrapped.



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I was confusing the Rifleshooter test with a video piece from Johnny's Reloading Bench or some such that appeared some months back and claimed mis/hangfires with SRP Creedmoor brass with Viht N550 loads. It was almost certainly a temperature issue as this was during the winter. The methodology was crap because the tests involved different ambient temperatures for the differing case types as well as very small sample sizes. He thoroughly confused me too by apparently doing a flash-hole reaming job on the SRP brass using what was obviously a large diameter uniformer tool for the 2mm size hole. This left me wondering what size US made SRP Creeedmoor brass actually was. My memory may be letting me down again, but I think this was Peterson SRP Creedmoor - and this company assures customers its SRP cases have the correct 1.5mm flash-holes.

This one is OK as far as it goes, but with large flash-hole SRP brass it's pretty pointless IMO. I like the Rifleshooter.com stuff - good down to earth nice builds without frills and they're genuinely pleased to get results under 1-MOA, and ecstatic to get half-MOA compared to the 'shoot quarter-MOA all day long if I do my stuff' pieces that have become the norm online it seems. A shame though about the images of the targets in this report - I tried making sense of them but to be honest gave up after a couple of minutes as I found them so hard to see.

So far as actual MVs are concerned in the cartridge, nothing surprises me too much these days. Years back I had a Dr Geoff Kolbe designed and made chamber pressure measuring device for review - it used an accelerometer to measure recoil speeds and software that converted it into pressure. All you had to do apart from attaching the sensor was to input rifle all up weight, bullet and charge weight, and finally the bullet diameter, shoot a round or two and see what the machine said was being generated internally. Out of scientific interest I tried a standard Small Pistol primer in a pretty well mainstream 223 Rem loading alongside the SR magnum I normally used. The SP model gave higher MVs and according to the Dr Kolbe device. around 5,000 psi higher pressure. When it comes to cartridge ignition, nothing is as it seems  ..... seemingly ☺️


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