First check to make sure that the gas block is 100% properly aligned with the gas port.

The next question I will ask is what length gas system are you running, pistol or carbine? You mention carbine but I'm unclear if that was just referencing the gun itself or the gas system.

If you have a carbine length gas system I would suggest that would be a large part of the problem to start. Also given that you are using an adjustable gas block there is a chance you may want to have the gas port in the barrel enlarged, but that decision should be made by a qualified gunsmith. The powders used in .300 BLK work best with pistol length systems for ultimate reliability. If you are using a pistol length system there is still a small chance the gas port may need to be enlarged. Most custom barrel manufacturers will recommend enlarged gas ports when using adjustable gas blocks.

The only time I have had an AR-15 give me gas issues was on a .300 BLK SBR build and my fix was embarrassingly simple. Always make sure the gas rings are not lined up with each other, with my malfunction all of the gaps matched up and the gun only cycled maybe once or twice out of about 15 shots before I stopped for the day to find out what was wrong.

Finally I would not worry too much about springs and buffer weights, I mean if you have stock ones laying around it can't hurt to try them out but I doubt that is the problem. As far as why the lighter faster loads were cycling and the heavies were not? A few minutes playing around in quick load shows me that the heavies are most likely running at a lower peak pressure from the factory and have almost 2500 PSI less pressure at the gas port (Quick quick load disclaimer, it's just a simulation and could be wildly off) so a gun that was on the verge of being under gassed suffers with just a simple change in ammo selection.

Just my 2 cents, take them for what they are worth.

 

I scoped the bore to check block alignment, did that after using a kaw valley gas block alignment jig, did one dimple.
Yes, carbine gas.
The GM M27 300blk fluted 16" carbine barrel comes with one of the largest gas ports I have ever seen, almost as big as the port in the GB.

Funny though, one post/review on GM site says had to ditch the adj GB and use std block. I wonder why that is?

Prior to Odin adj gas block it was running a std YHM gas block with std spring and buffer, and the 147gr ammo was bucking my shoulder.

I can re-scope the bore to look at gas port.
I suspect the issue I see is, gun powder.

 

To get my non-adjustable carbine gas 16" 300blk working, I used a KAK LIGHTWEIGHT AR15 CARBINE BUFFER SET
I forget which one I'm on, I think the middle one, to work reliably with full speed unsilenced, subsonic silenced. A heavy buffer will probably never work. The round is designed with certain parameters in mind and lots of gas isn't in the profile.

 

My H1 buffer cycles 110gr a-ok. 125's and 147's wont cycle good, or at all.
Buffer set is the after-factor, comes after knowing gas length and gas port size. An adj GB should allow no gas, to all gas.

IIRC, it was cycling 200gr subs, and 147gr supes, when it was std YHM GB w/ std carbine buffer & spring, but the 147's were bucking me, I assumed buffer was slamming back of tube (too much gas).

This 16" was meant for supes only, hence I wanted it to cycle 110/125/147gr.

 

I suspect ammo diff's are my enemy.
I will try Sellier & Bellot 147 Grain FMJ, it appears to be loaded fairly hot to get 1411 LB-FT at muzzle. The Hornady Vmax 110gr is 1378.
The 147 Armscor I was using is only 1800fps, the S&B is 2077fps, so some big diff in powder to get +277fps

300 Blackout Ballistics - Load Data & Chart

A look at 300 Blackout Ballistics including load specific data and a ballistic chart.

www.ammunitiontogo.com

 

I built both my AR's. My .300BLK is a 16" Ranier Match barrel; I use a Wilson Combat adjustable GB and carbine gas, and a AIM Surplus M16 type BCG, standard buffer spring and a H buffer. I can run 110's, 125's and 155's without making any adjustments, always get full cycling (no FTE or stovepipes). The 110's are about 2400 fps, the 155's run about 2000. I haven't tried any subs on my carbine, no suppressor so what's the point. I load using Lil Gun almost exclusively on the BLK.

My Grendel is a 20" Odinworks, with an Odinworks M16 type BCG, and an Odinworks adjustable GB, rifle gas. My loads are all 123 grain, for long range, MV around 2600 fps using CFE-223. I use a standard spring and H2 buffer, it runs just fine. I have the GB's open all the way on both guns.

 

Bullet weight and gas volume dont always line up. What matters is powder burn rate and port pressure.

From there you can start playing with buffer weights, springs, ect.

Take it back to stock and then change one thing at a time. Right now you have too many variables too narrow it down to just one.

Is it a pistol length gas system or something different?

Suppressor or no suppressor?

 

Is it a pistol length gas system or something different?

Suppressor or no suppressor?

carbine gas, 16"
no supe.