Originally posted by NikonUser:
Some thoughts for you.
The Colt probably has a (generous) 5.56 NATO chamber. It swallos everything and whatever you fire in it, grows to match these generous dimensions.
The Aero has a tighter chamber that easily accommodates factory ammo but has issues with fat cases fired in a NATO chamber. (Been there, done that.)
The AR-15 is very little camming action compared to say, a bolt action, hence the issues you have been experiencing.
Cases have a tendency to grow the more you fire them. I get 8-10 full (sometimes over loaded) power loads from my cases. To retard the case expansion, I long ago switched to small base on my match ammo caliber sizing dies (.223 Rem and .308 Win). I use these from the first firing. Never had an issue after that.
The case guage rules! If your sized case does not slip in perfectly in the guage, you need to figure it out. And you seem to have done that, so well done.
I suggest you spot check ammo at different times using that guage. Just to keep everything in check.
BTW, my regimen of F/L sizing cases with bushing and small base dies gives me the following: I slipped an 8X fired case (prior to sizing) into the case guage, and it fits right in. Yes, a case that has been fired 8 times (sized 7 times) with a small base die with a bushing. I think that is testament to proper sizing right there.
I'm glad you got it figured out.
Next up, you need an instant indicator comparator:
https://www.redding-reloading....nd-bullet-comparatorThis allows me to set my sizing die to provide a shoulder setback of .001 for my match ammo.