How hard is it to switch out gas blocks to adjustable ones?
Ar15 and 10 for suppressor use.

Simple. Very simple if you don't have to take the hand guard off

I don't think it's generally necessary on the average 556/223..

Some of the non traditional ar cartridges can be finicky. It might take an adjustable gas block and a heavier buffer weight.

What about building an upper in 300 blackout or buy one ?

Only you can answer that question. I enjoy building them and I like particular quality parts. My 223 that I have I I bought complete uppers and built the lowers. I bought them from the manufacturer whose handguards I prefer.

One day I'm going to pull the trigger(pun intended) on a JP Enterprise 556. That will be the only modern sportsman rifle I buy that I won't have a major hand in assembling.

Oh, I did buy a complete upper in a .20 practical from a local barrel maker that uses Shilen blanks. Didn't take long and I switched out the handguard, BCG and the cheap 20 dollar charging handle that came with it.

Right now I'm in the process of helping my son assemble a 223. He ordered a assembled upper and a barrel from Aero.

It will be a decent gun when we are done. He's debating on a Timney or Giessele trigger.

I've been dragging my feet on finishing a 6mm ARC I started a year ago. That is going to be a total assembly from scratch using a Proof Research barrel.

Ok its over gassed just a bit , most casings landed together but a few flyers, some brass on the forward assist where casings hit. What else should i look for as signs

.556 ammo.

I'm not a total expert on this stuff so take it for what it's worth. 1lessdog and ridge runner know quite a bit more than me.

I think the casings is a big tell, how much gas is in your face and of course accuracy.

If you have a basic flat top AR it's super easy. Really all you need is adjustable wrench for you muzzle device, and some allen keys for the gas block. All you do it tha the hand guard off , take the muzzle device off, pop your allen keys off your gas block , pull it off, sljnd the new one on , line it up and just re assemble... Legit like a 5-10 min job

What will you be shooting? If it's a 300 Blackout there is no need. As to me the 300 Blackout is best functioning caliber there is. If a 223 I would shoot first before you switch anything out. The only caliber I run a adjustable gas block on is a 6.5 Grendel.

Buy a Bear Creek Arms 300 Blackout and shoot it and see how you like it and how it shoots. I run Supersonic and Subsonic 960 fps and they shoot really good.

Should be easy if it is all set screws or clamp on. Removing a pinned block might be a little bit more difficult but definitely doable, the pins are tapered so they go in and out only one way. When installing watch that the gas ports are properly aligned as a canted block can block them.