It depends on several factors:
1. Type of barrel: mil-spec vs. match grade barrel
2. Presence of mil-spec front sight assembly and standard handguards
3. What do you call "hot"? 5 rounds in 5 seconds, or 500rds in 5 minutes.
I have a Bushmaster reciever with 16.5" "light" barrel. It measures 0.675" at the gas port. Before I replaced the factory handguard and removed the front sight assembly, it was around 3" at 100yds with good mil-spec ammo and/or commercial 55gr Soft Point ammo.
After replacing the upper reciever with a DPMS "Hi-Pro" reciever and gas block with a Yankee Hill Machine picitinny gas block and a Hogue free float handguard, I'm now getting 0.5-0.7" groups with "varmint" grade ammo and 1.5" groups with mil-spec FMJ ammo. It doesn't shift with heat up, and I don't run my guns till the barrel droops....... Mine is a "plinker" and varmint-hunting rifle that stays in a hidden corner in case an old "customer" comes for an un-welcomed visit. (retired law-enforcement officer...).