newbie 308 chambering problem

[divingin]

Crimping is not a bad idea when loading for an AR-10

While I sort of agree, it also may not be necessary.

Measure the OAL of a cartridge, load that into the magazine. Fill magazine, and shoot all but 2 (one in the chamber, one in the mag.) Measure the round remaining in the mag. Did OAL change? Now reinsert that into the mag and fire the penultimate round. Eject the final round from the chamber and measure OAL again. If it's different than when you started a crimp will probably be needed. If not, you can probably do without.

 

[Tommie]

While I sort of agree, it also may not be necessary.

Measure the OAL of a cartridge, load that into the magazine. Fill magazine, and shoot all but 2 (one in the chamber, one in the mag.) Measure the round remaining in the mag. Did OAL change? Now reinsert that into the mag and fire the penultimate round. Eject the final round from the chamber and measure OAL again. If it's different than when you started a crimp will probably be needed. If not, you can probably do without.

Thus my saying it is not a bad idea - as opposed to "necessary".

 

[lazyMlazyK]

Bill: From his post about sized brass chambering fine, I’m going the other direction. I think it’s the crimp.
Your “crimping” is most likely bulging your shoulder.
I don’t Usually crimp. A few months ago, I got into loading for my old 30-30 with a tubular magazine. I had trouble with the crimp and my RCBS dies. Too much crimp pressure was pushing my shoulders out.

Probably this ^. I had the same issue a year or two ago when I started loading for 6.5CM. Some cases would bulge a tiny bit at the shoulder, and some wouldn't. Therefore, some of the rounds chambered fine, some were a little stiff, and some you couldn't get into full battery. Took a caliper to the shoulder areas on those ones, and sure enough, they were bulged out. I needed to back off on my crimping by setting up the seating die differently.