Still diagnosing this for other causes but wanted to know if this is even an option.  Everywhere I look I only see extra power springs.

Basically, I've got a new build (my first large frame AR) that appears to be under-gassed.  I'm confident that the gas block is properly aligned as I took a LOT of care during the build but I will tear it down to confirm when I get the time.



Copy pasta from an email I sent to RifleSpeed support about a shorter gas pin.

Rifle build:
RifleSpeed RS7519 gas block
Faxon Match Heavy Fluted 18" .308win (rear dimple only, made with an SLR dimple jig)
     I haven't pulled the gas block to check alignment mostly because I don't know if 35rds is enough to leave a solid carbon ring and because everything lines up perfectly.  The gas block is perfectly centered in the SLR rail.
Aero standard nickel boron BCG
Aero standard AR308 carbine buffer and spring in carbine length tube
Firing Norma 147gr Tactical ammo and 175gr Golden Target ammo

Symptoms:
Unsuppressed, the rifle will cycle but never lock the bolt back. The most I opened the gas system was setting 2-6 because I didn't bring the spacer and 2-7 allowed for freeplay.
Suppressed, the rifle will lock open at setting 1-6.

Sorry no idea with that gas block. My 6.5 Creedmoor and 6mm Creedmoor did that and 8 increased the gas till it cycled unsupressed and locked back. No extra couple clicks or anything like thar.  That has them working suppressed as well,  so good by me.

Mine are both SLR's and setup and tuning was quick

Took the rifle to the range again.  This time with the smallest gas pin RifleSpeed has.

Still won't lock the bolt back without a suppressor.  So now I really need to change something with the reciprocating mass or spring.

Any suggestions?

Springs are cheap, get a $5 one and cut a couple of coils off so it is weaker than full one.

Been down this road. More buffer mass will close the operating gap between suppressed/unsuppressed use. Go light on spring to accommodate unsuppressed and you’ll probably start getting malfunctions suppressed.

Ultimately went with an Armalite (A5 length) receiver extension, heavy buffer and Armalite rifle length spring. Don’t even need to change gas settings when using a can.

Wouldn't a heavier buffer cause more issues with short stroking?  Do I need to pair that with a lighter spring?

Not with more gas.

The problem with the Standard LR-308 buffer in an AR15 carbine receiver extension is that you can only get about 4oz buffer mass, coupled with a stiffer spring. If you tune the gas for unsuppressed, you’ll be way over gassed suppressed. In my case, the brass would literally bounce off the deflector back into the receiver causing a stoppage. Messing with gas settings and springs I could not get an acceptable setting for both suppressed/unsuppressed using the LR-308 carbine components.

I had a Vltor A5 RE (same length as AR10), made a solid stainless 6.5oz buffer and an AR10 rifle spring. Result is perfect operation with or without a can. Barrel is 16”Ballistic Advantage with Superlative Arms gas block.

I see.  Well the problem I'm having right now is getting enough gas in the first place.  At this point I probably need to get a regular gas block just to verify it can cycle naturally.

I would also measure the gas port as well when you check/swap gas blocks and compare it to what the manufacture says it should be. 308s are always overgassed, so if you are having trouble locking the bolt back then something is wrong.

Do not band-aid the problem with a weaker spring.

Your problem sounds JUST like AR15 rifle gas tube was used instead of AR10 rifle gas tube on an AR10 rifle gas length system. What is the length of gas tube inside your upper reciever?

Also, I used JP SCS Gen2 308 with light, medium, and heavy springs with the Superlative Arms gas block. Spring weight did NOT change what setting locked the bolt back on empty. Large frame ARs are much more mass regulated than small frames, and not very spring regulated.

My experience with the Aero carbine buffer and spring was the buffer is too light, it was even lighter than the advertised weight. I ordered up a heavy buffer and spring from heavybuffers.com which was about 2 ounces heavier. I also had to open up the gas port which was undersized on my Wilson Combat barrel. I don’t run a suppressor but it now runs flawlessly on any ammo I feed it.