I purchased my first AR almost a year ago. It was an almost new Colt cr6920( I think). A couple months later I purchased a complete Anderson lower and a radical arms upper and a bcg and charging handle from Palm State. Recently I felt the urge to attempt my first build. I bought a stripped lower and upper from Palm State Armory, a pencil barrel with low profile gas block and kits and parts from other places. I thought after this, I would be done. Yeah well not so much. I have been told a 300 blackout upper fits on an AR lower and operates even using the same magazines. My question is : will a 300 blk barrel fit onto a standard AR upper? Do I need special handguard gas block etc. Any helpful info would be appreciated, hints, drawbacks, advice etc.  thanks Andy

The only part that's explicitly different is the barrel.

This

Barrel, muzzle device (and washer), and probably the gas tube (pistol vs carbine or mid-gas length).