I have just come into a fairly large quantity of Win Large Rifle MAGNUM primers. Has anyone ever used magnum primers in a 6.5x55 load. I am reloading for a Ruger MkII and use slow powders, mostly RL-22 and H4831. I feel like the Ruger will handle the likely increase in pressure but will accuracy likely suffer?

My normal load is 48gr of RL-22, Rem case and WLR primer behind a 140gr GameKing at around 2650 fps.

Thanks in advance for the replies.

Depending on what data sources your using some will call for magnum primers for use with spherical powders like h380, 748, etc. I know the
Speer manual recommends magnum primers when using these powders. Is the swede the only cartridge you load for? Otherwise if you know anyone else that reloads maybe you can sell to them.

I also reload for an M1 Garand and aRemington 7400 in 30.06, a 45acp and a 41 mag. From what I been able to read, I can probably use the magnum primers in the Garand since there is a possibility of slam fires with regular primers. I have never experienced a slam fire in the Garand, though.

Thanks for the reply.

You can use the WLR magnums in the M1 with no problems. The Milspec CCI-34 primers which are made for M1s, M1As and other autoloaders are actually magnum primers. Slamfires aren't an issue with Winchester primers, or most any other primers so long as you seat them below flush.

You can use a Mag primer in ANY cartridge that take the large rifle primer. Just remember, as always start low and work up.

With a powder that burns that slow, I would use the WW Mag primer. I use mostly IMR 4831 and IMR 4350 in the Swede although I have tried many others.

No, not in the 6.5X55. However, I have used magnum primers in some cases of comparable capacity and caliber, such as the 7X57mm, with slow powders like RE22, MRP, and N205- not that the round needed them, but they were all I had at the time. I encountered no problems from excessive pressures, etc. But I did drop the beginning powder charges a couple of grains more than usual when starting to work up loads. In actuality, I could detect no real differences in performance that could be attributed to the use of magnum primers in smaller cases, and my previously developed maximum loads could still be used......

I don't believe you ever will, either! The Garand's firing pin has a shoulder on it which engages a cut in the bolt so that the firing pin cannot move forward to touch the primer until after the bolt is cammed into the locked position. If an M1 slam-fires due to the firing pin striking the primer, there's something wrong with the rifle!

Of course, as Briman noted, if the primer is not seated flush with the case head, a problem could result. But this is an ammo problem. Magnuim primer cups aren't necessarily any tougher than standard primer cups......