Hello,

Just went to the range tonight and ran 170 rounds through my brand new STG 77.

With Remington UMC 223 Brass ammo had 20 FTF out of a box of 50 on both settlings

Ran 100 rounds of federal 556 and ran fine

Anyone have these issues?

Thank you

AUGs have really strong recoil springs when new. Run some more full power 5.56 through it then try the weak UMC stuff again

Along with the above advice, try storing it with the carrier locked open.

Thank you, what is recommended for full power 556 ammo to break in the rifle

UMC is garbage ammo. I'd rank Russian ammo above UMC.

On a related note, my 20" AUG would intermittently fail to lock the bolt back after the last round. Using a variety of M193, M855 and Wolf Gold in AUG mags and Pmags it would happen about every other mag change. This went on for a few hundred rounds, then I turned the gas setting up to the adverse setting and fired a few hundred more rounds with no issues. Turned it back down and it's been fine since.

Like someone already mentioned, these guns ship with very strong recoil springs and feel very tight. So use full power 5.56 and maybe even turn up the gas setting to break it in a little faster. I couldn't tell the difference between the two gas settings when shooting, there was no perceived difference in recoil or anything to me.

Very likely because your rifle is new as others have stated. I've shot plenty of the UMC ammo and it was fine. I do shoot with a suppressor, so there's that .

XM193 is my "if it doesn't work with this something is wrong" ammo for testing new rifles

I'll echo the UMC ammo being garbage thing. I shoot primarily PMC Xtac m193 in my AUGs and have never had a problem with it. I've also used m193 prvi partisan with no problems.

I'm just here to bag on Remington ammo.  Learned my lesson on their pistol ammo, but it seems their suck transcends calibers.  OP, if it ran fine on Federal, you have your answer.

This.

Also are you using Steyr mags?

I have run 400-500 rounds through it now and runs perfectly

Great to hear.