A bit about chambers, don't know if this is on topic or not but file it in the "for what its worth department"
Lot of talk about 223 chambers being tight vs the 5.56 chamber. Don't know for sure, I can only report on my chambers.
I have a Mann Accuracy Device (used by the military for testing ammo) I obtained from the CMP. Remington Action and Kart Barrel.
It's a TIGHT 5.56 chamber. If it isn't clean, it wont accept a 223 "go" gage.
About 1/3 of the pieces of new Winchester 223 brash wont chamber in the Mann device. It chambers in my two ARs and my Rem 700 Bolt gun.
I have to resize the new brass with a SB sizing die to use it in the Mann Device.
If I fire any ammo in my two ARs the brass wont chamber in the Mann Device. However if I fire ammo in my Remington 700 Varmint, I can get it into the Mann Device.
This Remington BDL Varmint is the rifle I carried as a LE Counter-sniper rifle. Got it in 1978. The ammo I carried and used in that rifle was M-193 5.56.
I shot it quite a bit wanting to keep in practice and constantly confirming zeros.
I had access to a lot of M193s back then and that's about all I shot. But the chamber is still, after nearly 35 years, the Remington Chamber is still tight enough to get the spent brass in my super tight Mann Chamber.
One of my ARs is a SP1, I've had it a while and have shot thousands of M193 out of it.
My other AR is a White Oak Service rifle. I got it later in life when I had to furnish my own ammo. Can't tell you much about it and M193, only fired a few rounds I found laying around.
This doesn't prove anything to anyone but me. I don't care what I shoot in my 223s, be it 223 or 5.56, in my rifles.
Do what makes you feel better.
We all have different opinions, That's good, if that wasn't the case we wouldn't have anything to talk about.
I doubt I get any more 223s, and I highly doubt I'll go back into the NG where I can have access to 5.56.
I'll just keep hand loading what ever ammo my rifles like and shoot accurately.
CPT USAR Ret
USAMU Sniper School Oct '78
Distinguished Rifle Badge 1071