16" carbine 300blk, std gas block, FA bcg, no brake, std ammo (not subs).
Shoulder getting a bit beat up after 25rnds, mule kicking.
For a 1st adjust, should I try a heavier buffer or a heavier spring?
Which buffer and spring are you using now?
Brownells
078-000-337WB AR-15 Carbine Buffer 3oz (modifiable weight capable)
100-028-014WB Luth-AR BS10A AR-15 223 Carbine Buffer Spring
Perhaps the AR-308 carbine spring is the right choice?
What barrel?
Green Mtn 16" GM-M27
I would start by trying an H2 or H3 buffer or the equivalent buffer weights. That is close to the original buffer mass the gas system was designed for.
You are spitting out two to three times as much bullet weight with supersonic 300 BLK, it’s going to kick more than a 5.56 carbine.
A regular carbine spring and H or H2 buffer should be correct.
I gonna switch in some tungsten weights for H3, and then back down from there if needed.
But yes, I do expect more kick from 300, but not this much. This 300blk runs good, now just doing some fine tuning.
I feel very little reduction in recoil when I compare a carbine buffer to an H1, or an H1 to an H2.
The addition of a brake should provide more reduction.
I would think that changing buffer weights will NOT change the felt recoil that much, if at all.
Yes, the bolt speed will slow down with a heavier buffer. But if you think about it, a heavier buffer would be more weight moving slower, a lighter buffer would be less weight moving faster. Tit for tat = the same felt recoil to the shooter. The bolt has to cycle.
Additionally, realize the buffer and recoil spring will receive their full cycle command through the BCG from expanding gas during the dwell time. You cannot change the dwell time without changing the barrel length. But you can alter the dwell time’s effect with an adjustable gas block or muzzle device.
I would start with a brake to reduce felt recoil. Double up on ear pro
Contact Clint with Black River Tactical and get his input. He’s a member here.
https://blackrivertactical.com/WP/Adjustable-Gas-Drive-c6464009
He produces “Adjustable Gas Drive” gas tubes that do work with over-gassed barrels.
If your barrel is over-gassed, that’s the easiest, proper, fix from my experience.
If I run into over-gass issue I usually swap to an adjustable gas block.
Energy is related to V^2. Faster moving buffer slamming the back of the tube creates a impact force (mule kick). Slowing it down removes the impact, but not the overall energy, thus it’s not a hard mule kick, but more of a heavy push. Just heavy enough to let it cycle good. My buffer at 3oz is probably just too light.
I will be looking at brakes, but a special setup with a brake, just not there yet.
Adj gas block as last resort on my list.
Will try buffer 1st and go from there. Always fun trying to fine tune stuff.
This is my suggestion. One and done, no messing around with weights to mask the root cause.
Any chance you measured the gas port? Does it cycle subs unsuppressed?
I am also a happy user of BRT EZ Tune gas tubes.
A 16” carbine gas 300 BLK can’t really be over gassed. The gas port is functionally as large as the gas tube. For example a 14.5" with carbine gas will be reliable with some ammo and unreliable with others, so most make them with pistol gas.
Now mine is a little different, 8.5" barrel.
I run a SpringCo White spring and a H2.
Another thing too. What stock you using?? Magpul??
might want to check out https://limbsaver.com/collections/firearms-products
Not to be ugly, but I would start with your shooting form/technique. My 8" 300BLK started with a carbine buffer on a pistol length gas system and no brake, and I wouldn’t consider it to be “mule kicking” in any way shape or form. To the point where I can’t imagine how anyone would describe it that way?
I ended up with an H3 buffer to slow down the carrier a bit with hot supers, but don’t notice much change in felt recoil.
I would bet the carrier key is striking the lower.