I've got a recently finished 8.3" .300 blackout upper with a Superlative AGB. My intended suppressors for it are a Resonator K for HD and a Recce 7 for not bothering neighbors. I'm trying to figure out whether to tune it for use on my carbine-buffer SBR lower or my A5 SBR-lower.

My question is, if you're adjusting the gas block, does it really matter if you have an carbine vs. A5 or what buffer weight you use? I think Superlative recommends using a carbine buffer weight and adjusting from there, but I've seen some people advocating for still using heavier buffers with an AGB. It seems like that just adds more reciprocating mass and makes the gun jerkier to me. Any recommendation on where to start? If .300 BO ammo wasn't so expensive, I'd mess with all the combinations, but looks like it could be a long time before we see cheap ammo again.

Yes it matters.   With a heavier mass, you'll need more gas to move it from rest. That mass will also slam home with more energy.

Lots of folks say use a heavier buffer to try and delay the bolt opening, but what Superlative recommends makes a lot of sense too.

Don't forget that while the A5 setup is also using a heavier bolt its slightly longer compared to a carbine buffer, the tube is slightly longer and the spring is meant for a 308 application.  Its not the same as just throwing another tungsten weight or two into a carbine buffer assembly.

@amphibian

I trusted this guys advice and did the A5 tube with the Tubb flat spring and the hydraulic 9mm buffer for my CMMG radial delayed 9mm.  He also suggested that it works pretty good for a suppressed 5.56 setup which I happen to share that particular lower with and it absolutely works perfectly.  Smoothed things out nicely.  With a 10.3 crane barrel meant for suppressed shooting I've never felt the need to use an adjustable block.  Just another alternative for you to consider.

https://c3junkie.com/?page_id=280

This.

I run

A5 tube
Kynshot RB5007 buffer
Tubbs 556 flatwire spring
SLR AGB to further tune the gas.

Depending on your blackout barrel (port size and dwell/barrel length), subs with no can may barely cycle at all with a carbine weight buffer.  With adjustable gas and a can you might find optimum tuning for subsonics with a carbine buffer doesn’t require choking off much gas. SuperSonics tend to benefit more from adjustable gas with blackout.

Reciprocating weights in the buffer are primarily to control bolt bounce in full auto and changing reciprocating mass can tune the cyclic rate. A hydraulic buffer deadens the buffer bottoming out and delays return stroke for both recoil dampening and cyclic rate reduction. A longer stroke from modifying the cam path and bolt carrier such as Surefire optimized bolt is another technique useful on full auto guns. I doubt these augmentations provide much benefit for semi auto firing of 300 blackout.

I’d recommend starting with a carbine buffer.  The original AAC barrels functioned in all 4 modes (with varying degrees of “gassiness”) with just a carbine buffer.  By all 4 modes I mean supers and subs, suppressed and unsuppressed.

You already have an AGB and carbine buffer right?  Why not start there.

Sure, you could buy an A5 tube, hydraulic buffer and Tubbs spring, but what is all that going to cost?  How much ammo would that pay for?

I don't care if it runs unsuppressed subs. Mostly just concerned about reducing gas to face and recoil for supersonics.

I've got a stock Colt lower (carbine buffer tube, H1 buffer I believe, and factory carbine spring) and an A5'ed lower (A5 buffer tube, A5H2 and A5H3 buffers, and a Vltor spring, which I think is just a factory rifle spring). Neither is full auto.

My question is really if there is any reason to start my quest with the A5 setup? Seems like it would just require more gas and have more reciprocating mass than necessary or is there some other benefit I'm missing?

minimizing bolt bounce full auto. doesn't sound worth it for your application.