Reloading Issues

[GRH]

Where is the datum measuring on your fired Brass?

I would guess your chamber is just fine,
Your dies on the other hand seem to be limiting you from adiquitly setting the shoulder back. This could be the dies or the shell holder, Though I expect the die is the issue at hand.

If we trust your measurements are accurate & honestly I am just a bit - skeptical not knowing the measuring tools or your comfort level using them, then your dies are resizing your brass at least .005" long. for an AR rifle IMHO. Zero clearance is unacceptable in any rifle IMHO. Personally in an AR I think Id be targeting about .004" to .005" clearance for your headspace.

So Id be hoping for .005 difference between your fired brass & the resized brass. of course you want the resized brass to be shorter.

https://6mmarc.com/showthread.php?tid=195

I am using the Hornady Headspace comparator tool and case gauge. I modified my shell holder a bit and can get the headspace/datum measurement down to 1.181 now. Anything longer than 1.184 at the datum line will not chamber but I have them all sized at 1.183 now. The necks are a bit long but I need to trim them all down anyways as most of them are 1.491-1.493. For testing seating depth I also use the lock n load modified case tool. I reload for 223, 6.5G, 300BLK. 45-70, 450BM, and 350 Legend as of right now. I've had the ARC for a little over a year and have been going through factory ammo and am just getting started with it as far as reloading

SAAMI 1.190  -.007 cartridge ogive (.350) so it sounds like your chamber is near the low tolerance limit.

As long as you can get the shoulder pushed back for that chamber, carry on... it's all part of the game.