I’m looking at 300 blackout options that would be run suppressed and primarily shooting sub-sonic rounds, likely Gorilla’s 205 grain hollow-points.
I’m strongly considering an Aero Precision M4E1 and swapping the muzzle device for my suppressor. I’m also considering a PWS Mod1 MK109 because it has an adjustable gas block. I’m just unsure of the importance of having the adjustable gas block as not many uppers seem to offer it. Which that could be the answer to my question but figured I asked the community for feedback. Best!
My Savage .224 Valkyrie AR came with one already. You can fine tune the BCG to reduce recoil, wear and tear. Depending on which grain I’m using. 75 for practice, 90 SKMBT for 1,000 yrds.
If your BLK doesn’t cycle correctly with a Can you can fine tune it with a Block instead of buying boxes of different ammo trying to find one that will be reliable.
Why don’t you just install an adjustable gas block on whatever you get?
I’d guess most manufacturers don’t put them on because it would increase the complaints from people fiddle-farting with it, not knowing what they are doing.
You can run it without an adjustable block, but it’ll be more gassy than an 87 suburban. Can also cause excessive wear. I agree with @Barry54 , just get an adjustable block for whatever you buy. Aero makes a nice one
When you really get away from factory/stock oem design you need an adjustable gas block.
Make sure you get a pistol length gas system for 300 no matter what barrel length you choose if you want subsonic to cycle.
Here’s an example of an ultralight buffer that requires an adjustable gas block. Paired with an aluminum bcg from PSA you could build a sub four pound ar relatively cheap and easy.
Not difficult. You want your cases to eject between 3-4 o’clock, so start wide open and go down from there. If your barrel doesn’t have a dimple for a set screw, the toothpick method is affective.
Swapping blocks is easy, main thing to watch is not losing the roll pin that holds the tube in the block when you drive it out. No springs so not really an issue. Skinny punch, small mallet and an allen wrench, and 20 minutes tops for a swap.
Thermal cycle can cause the set screws to loosen over time. I loctite every gas block set screw on every build I do. They are a pita to remove if you don’t know how to free the loctite…if you try to force it loose, you’ll strip the head or give your Allen wrench a fancy looking twist, but a little heat from a butane torch softens the loctite, and you can get them out with a couple inch pounds of torque.
I would assume their gas blocks are steel, but if they are aluminum, the heat would be detrimental technically. I’ve never had a problem heating aero blocks.
Specifications:
Machined from 4140 steel
Nitride coated
Compatible with barrels utilizing a .750 gas block journal (.625, .875 and .936 coming soon!)
Attaches to barrel via 10-32 x 3/16 knurled set screws
Includes:
Assembled Adjustable Gas Block
One 6" 3/32 adjustment wrench for easy gas block adjustment underneath installed handguard
Replacement spring and detent included
Please note: We do not recommend the use of red threadlocker on the threads of the set screws. If you decide to use threadlocker we recommend using the non-permanent variety.
*DO NOT USE THREADLOCKER OF ANY KIND ON THE GAS BLOCK ADJUSTMENT SCREW.
They are steel so you’re good. I think they say that because people loctite and then they can’t get the block off if they want, and mess stuff up trying to force it. Definitely don’t use loctite on the adjustment screw…you’d regret that one…
I have an extra set of detents, springs, and 3 extra gas tube pins. Mostly because I’ll order extra parts if I have to spend a little extra for free shipping. It’s convenient if you accidentally launch a spring/detent into orbit.
. I hear he’s got roll pins. 
(Plus pretty sure I could set up a 600 yard range)