Small Rifle Primer Strength

[Laurie]

This thread ties in with an ongoing discussion over on the 'Long-Range Target Shooting' forum on the new Lapua .308 Win Palma case with a small primer pocket.

http://www.usrifleteams.com/lrforum/index.php?showforum=62

After testing by the US Palma team using some of 1,000 prototype cases supplied by Lapua - identical to standard 308W Lapua production apart from the smaller pocket and flash-hole diameter, both Dan Simpson and Tom Whitaker report much reduced velocity ES and SD values with a small reduction in MV that can be compensated for with another 0.2gn on the powder charge. Interestingly, Dr. Whitaker goes further in quoting advantages for the use of small primers:

All the testing we did confirmed what I experienced with the Rem BR case. Much better ES, SD numbers and no primer senitivity. That is that all primers gave good numbers I tested 4 different brands of SRP's bought off the shelf and a local store and all gave significantly better chrono numbers than any of my "select" LRP's (SD + 4-5, ES 12 -18). SAMMI specs do not specify primer size for 308 Win. As a final note I shot the first Palma match at Phx. this weekend using these cases. First time across the Palma course in COLD weather my score was 450X30. Lapua is releasing these cases at the Shot Show and they WILL be available world-wide.

I'd always thought SR primers were at their limit in a .308W size case, but apparently not with today's products. What I find particularly interesting is the reference to reduced sensitivity to production lots, unlike LR versions.

Laurie,
York, England

 

[cliffy]

WHAT'S all this gobblety-gook? Things work or they don't! CCI 400 and Remington 6 1/2 primers fail all my hyper-velocity tests. MAGTECH 7 1/2, CCI 450, I'd suppose ALL "so-called magnums with a cup thickness of .25" somehow seem to PASS my hyper-tests." Once one blows through a primer, one should take note of the primer USED. Twenty-six, point two grains of Alliant ReLoder 10x powder pushing a 36 grain Barnes Varmint Grenade, should not BLOW-OUT a primer with a mere 1-in-12" twist in a bolt-action .223 Remington! Color me hyper-speed, but color me semi-sane, and experienced. Cliffy