misfires with Rem 7 1/2 primers

[Webster]

I recently loaded 20 brand new, never fired Lake City 5.56 cases using Remington 7 1/2 bench rest primers. Shot them today and had 5 misfires (out of 20 rounds) in a Savage 10 bolt gun chambered in .223 Rem.

Pulled bullets and dumped powder from the 5 dud rounds and loaded the empty, primed cases into an AR-15. Four of the five primers went off.

Any ideas what may be causing the misfires in the bolt gun?

Am seating the primers about 0.006" below the bases of the cases and it looked like they were getting good strikes. (see attached photo below)

Thanks for any suggestions.

There is no proper depth of seating measurement. I had the same problem. Seat by feel to the bottom of the pocket and they will always go off. Some people say seat to the bottom of the pocket then some crush whatever that is. I uniform my pocket depths. Each case has a slightly different pocket depth since the pockets are swaged in. They are not machined. If they are not seated to the bottom of the pocket some firing pin energy is absorbed pushing the primer in deeper. If the primer is seatd to the bottom of the pocker 100% of the firing pin energy is used to crush the priming compound. I have a feel for how hard to push after priming for 45 years.

 

[Webster]

Gotcha. I place cases in the oven at 250F to make sure they get dry.

The misfires in my rifle were almost certainly due to light primer strikes. A heavier striker spring fixed it and all is well.

250F won't soften or damage the brass. I used to dry cases in the kitchen oven at somewhere around 225F. I now I dry at about 190F, less oxidation and the cases are brighter because there is less oxidation. I have gone to the extreme of blowing out each case with a DustOff air can. I was surprized how much water can stay in the case after shaking them by hand. I don't tumble cases very often. I put them in the oven for 2 hrs at 190F fthen turn the oven off and let them come down to room temp over nite. I probably reload about 500 cases a year. 95% bench rest 5% at varmints. I usually shoot about 30 shots each trip to the range. 10-15 times to the range each summer.

 

[rogn]

mikecr

In the reloading manuals they tell you to never use cases used with reduced loads again with full powder loads.

This is because with each firing the case becomes shorter every time the firing pin hits the primer, meaning the case shoulder is pushed back.

If the reduced load cases are used with full power loads it is possible that you will have a case head separation.

The amount of shoulder setback varies but I know some of my milsurp rifles can make the case over .001 shorter each time the firing pin hits the primer.

Below a 7mm Mauser long in the tooth just under maximum headspace with factory loaded ammunition. Notice how far the primers have backed out of the primer pockets. In this rifle you have long headspace and short factory cases and still have good firing pin hits.

My guess is the OP did not seat the primers properly and they moved and blunted the force of the firing pin hit.

They had better pass that warning ahead to all those people that have fireformed cases, especially those using COW.

 

[memilanuk]

They had better pass that warning ahead to all those people that have fireformed cases, especially those using COW.

I'm guessing that the folks fire-forming cases are probably not the target audience that those reloading manuals are written for.

Plus, fire-forming cases is generally a one-time affair - you typically aren't firing them multiple times with COW. I'm sure there is that *one* guy, though...

 

[Uncle Ed]

When repeatedly shooting reduced loads the firing pin has enough force to push the case shoulder back each time the case is fired. My reduced loads in some of my rifles will be .001 shorter each time they are fired. (Its firing pin shoulder bump)