6.5 Creedmoor Cases Large or small primer pocket

[The Badger]

Hi folks can any one advise on the performance difference in large and small primer cases with the Creedmoor. I have been advised to expect slower speeds with lapua small primer cases.

Can anyone advise,

If using small primers should you use standard primers or magnum primers

Thank in advance

[Laurie]

Yes, you'll see a reduction in MVs for any given charge weight, or to turn it around you'll need to use slightly higher charges than shown in the manuals or you previously worked up to with standard LRP brass.

The difference in terms of equivalent charge weights for the two types depends on the cartridge, the powder used, and the bullet weight. For a long time, I reckoned on a half grain difference in 308 Win between the case types with IMR-8208XBR and H4895 with 155s, but in a SR primer test series I ran with small primer 'Palma' 308 brass that started with a like for like comparison between Lapua standard and Palma brass with a 167gn Scenar and Viht N150 load combination, the difference now turned out to be 1.4gn to get the same velocities.

Use SR magnums or BRs, or to put it another way, avoid the CCI-400, Rem 6 1/2, PMC SR / Murom KVB-223, and possibly the Winchester WSR. They have 0.020" thick primer cups (WSR 0.021") while others have 0.0225" (Federal 205 and 205M) and better still 0.025" (everything else). That 5 thou' cup thickness is the difference between a primer that copes with 60,000 psi + pressures and one that craters badly or worse 'blanks' the primer.

The other issue that may arise is that some rifle actions simply cannot cope with a full-pressure modern cartridge with SR primers due to firing pin thickness, profile, and its fit in the bolt-face aperture. I have an FN SPR that is fine with LR brass, but will produce serious cratering and some blanking 2-3gn shy of Viht's not exactly hot maximum loads in 6.5X47L, and that would apply equally to the 6.5 Creedmoor, 6BR etc. It is a 260 now and lives happily with 60,000 psi with the LR primer type (don't ask me why!), but it means I can't use the Peterson Cartridge Co. SRP version when it gets here.

The corollary of all this - my leitmotif and risking becoming boring to me as well as those I pontificate at - is that if you have worked up a 'hot load' in SR brass, (or one anywhere near maximum levels) DO NOT TRANSFER IT TO AN LRP TYPE CASE WITHOUT A SIGNIFICANT CHARGE WEIGHT REDUCTION.. You WILL produce significantly higher pressures in the LRP type, and moreover you've moved to a case-form with a weaker case-head less able to withstand very high pressures.

[VarmLR]

I can only echo what Laurie has said as my findings have been very similar.  The difference between SR and LR brass in 6.5 CM using magnum primers/RS62 for the same velocities was almost two grains difference (just under) with 44gr required in SR brass needed to get the same velocities as just over 42gr in LR brass.  ES was a little tighter in SR brass, and the jury's still out on how long it lasts before primer pockets start to get loose.

[Triffid]

I must confess to struggling a bit with this question myself. . .

I've been loading 6.5cm in large rifle brass - mostly fire-formed Lapua 22-250 - using H4350 and the 142gSMK for a couple of years, but when my stock of H4350 runs out I'll change to RS62 and the 139gn Scenar. I was thinking of getting new brass at the same time and initially was going to get the Lapua small rifle version. I'm using a RPR out to 1000X on Stickledown: I haven't done 1200X yet, but it's a possibility.

But these issues with small rifle primed brass leads me to question whether I should bother, but just stick to Large rifle primed brass.  I don't want to make the mistake of chasing velocity over accuracy but everything I've read indicates that I'll sacrifice some precious fps if I switch to small primers. I'm quite a cautious reloader, who hasn't strayed outside the powder manufacturer's maximum loads before. 

Will moving to small primers give me any (significant) advantage?

Triffid 

[VarmLR]

If you use a double base instead of single base, you'll up the velocities and should still benefit with the promise of smaller ES/SD.

Personally, if I could get around 8 to 9 reloads from LR brass, I wouldn't bother going the SR brass route again.  Don't know what folk are getting out of theirs as I have hung my hat, for now, on SR primer brass and waiting to see what I get from those.  I find with 139 Scenars, 2650fps is still bettering the results achieved with my 308 loads which were to the same velocity using 175TMKs, but others shooting 6.5 LR brass to over 2800fps do benefit from less wind drift...more shots into the V-bull in variable conditions as long as very tight ES is maintained.  You pays your money and makes your choice.  The lighter scenars driven faster seem to do just as well so I'm debating whether there's really much advantage in the 139 at all, especially as it takes up more valuable case capacity if loaded to the same COAL.

[The Badger]

Hi chaps thanks for your comments. Laurie your knowledge on the subject as usual secound to none. I tend to agree with VarmLR there appears to be little advantage in paying the extra for SR  brass.

Any addition comments appreciated.