Case Shoulder & Pressure - Belted Mag

[blauber]

I just started loading 7mm Rem Mag with mixed results. Started with new WW brass and loaded 25 rounds from 64 to 66 in .5 gr increments with NO pressure signs. 65 gr looked promising. Next outing I used the once fired brass and looked for the magic - started at 64.8 gr and worked up in .3 gr increments to 66 gr with NO pressure signs. 65.1 gr looked promising.

Ok, so next 25 rounds - I backed off the lands in .005" increments to .020" - .015" looking good. I loaded this set of 25 rounds at 65.1 gr but started experiencing pressure signs (shiny ejector mark, sticky bolt). So today I loaded at 65.0 (backed off .1 gr) at .015" off lands and again experienced pressure signs (brass is now 4x fired). The majority of rounds needed a little extra "oomph" to close the bolt. It shot ok, but some fliers too.

So today, thinking that I need to FL size -I measure the hard to chamber rounds with a headspace gauge at 2.122" and settled at bumping back to 2.119". Now, all brass chambers like a dream. I am aware the 7mm rem mag headspaces off the belt - at least when brass is new.

My question is, could these fliers be caused by a hard chambering case? Or are belted mags typically more prone to accuracy issues from cases that vary slightly at the shoulder? I will be back at it soon but now have to wait for my projectiles in the mail

 

[Fire306]

I always full length resize. Only bumping the shoulder .001" if you can set up your dies to do it.
Just because the Belted cases headspaces off the belt, doesn't mean the shoulder doesn't grow and cause the case to jam in.
I reload belted cases the exact same way I load any other cartridge.

 

[blauber]

I forgot to mention that I don't FL size - only when needed...use a collet to neck size then FL/bump the shoulder back when hard to chamber (usually 5x fired). I FL and bump the shoulder in one step using a Redding body die. Maybe this 7mm could benefit from FL sizing; based on my other calibers they shoot lights out with just a collet neck size until a bump is needed. I believe I read the 7mm has very high bullet "exit" pressure (say over a .243).