View Full Version : 300blk mule kicking
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?
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.
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
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.
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.
This is my suggestion. One and done, no messing around with weights to mask the root cause.
Green Mtn 16" GM-M27
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
Matt in TN
01-28-21, 14:25
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.
Any chance you measured the gas port? Does it cycle subs unsuppressed?
I am also a happy user of BRT EZ Tune gas tubes.
I did not measure it, but their spec is 119-121. Visually it did look like ~1/8".
I have not shot subs in this rifle, I do not plan to shoot subs in this upper set.
Another thing too. What stock you using?? Magpul??
might want to check out https://limbsaver.com/collections/firearms-products
It has a Hogue 15240.
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 am well versed in form & technique, so I don't think it's that.
My 3006 bolt kicks, but this 300 seems to kick even more than that.
I don't expect overall energy in the bcg to change at all unless I use adj gas block. I think I am just feeling an impact pulse due to light buffer and/or spring. I'll work through tuning it.
I am well versed in form & technique, so I don't think it's that.
My 3006 bolt kicks, but this 300 seems to kick even more than that.
I don't expect overall energy in the bcg to change at all unless I use adj gas block. I think I am just feeling an impact pulse due to light buffer and/or spring. I'll work through tuning it.
For the hell of it take the gas tube out and rotate the gas block 90 degrees and shoot it. Playing musical buffers/springs won't lessen the recoil you have as a single shot. A good and loud comp will reduce the push/jump but it ain't gonna make it a new rifle.
For the hell of it take the gas tube out and rotate the gas block 90 degrees and shoot it. Playing musical buffers/springs won't lessen the recoil you have as a single shot.
I need to try that sometime. I assumed that the BCG and buffer being accelerated back should counter some of the recoil and spread the force over a longer impulse, making it feel softer even if the recoil energy is the same.
You have to look at it this way... The bullet is out of the barrel before the bolt moves rearward more than a very small fraction of an inch. Gas pressure isn't pushing the bolt and buffer back momentum is. How far does the bolt move rearward before the gas tube is disengaged from the key and the pressure is reduced to zero?? Not far.
That momentum in the BCG and buffer has to be balanced by momentum in the opposite direction, transferred through the bolt face to the rest of the gun, which must reduce the instantaneous rearward velocity of the receiver and stock. The rearward BCG/buffer impulse is then re-imparted over the time that the action spring compresses. Recoil remains the same but it should feel different.
bamashooter
01-29-21, 18:49
Very strange. I've only fired one which was mine. 9" barrel with 0.102" gas port, basic carbine spring, H3 buffer. 125 and 144 supers. For me and a couple of buddies, we all felt it actually shot softer than several of our 5.56s (carbines / pistols) with basic ammo. The guy I sold it to weeks ago felt the same. He came over and fired a few and was near giddy with how soft it was. I just figured that's how they are; evidently not all. Hope you get it squared away.
Very strange. I've only fired one which was mine. 9" barrel with 0.102" gas port, basic carbine spring, H3 buffer. 125 and 144 supers. For me and a couple of buddies, we all felt it actually shot softer than several of our 5.56s (carbines / pistols) with basic ammo. The guy I sold it to weeks ago felt the same. He came over and fired a few and was near giddy with how soft it was. I just figured that's how they are; evidently not all. Hope you get it squared away.
Well, my 1st initial issue on this 300blk was a misaligned gas block. It was cycling light and 1 in 4 would not strip a new round. Bore scope w/ 45 mirror showed me the gas block was not aligned. Re-aligned gas block and it began to kick hard. The M27 barrel has a huge 120 gas port.
If your block is misaligned a smidge then perhaps that's the reason why your recoil appears light?
That sure sounds like it is over-gassed to me. Get one of these? https://blackrivertactical.com/WP/Adjustable-Gas-Drive-c6464009
The initial recoil should have nothing to do with the recoil spring or the gas system. The initial acceleration of the projectile, and the attendant opposite reaction, takes place before the gas port is reached in the barrel, meaning the bcg is still locked in position. Nothing can be done to mitigate that recoil except to load lighter projectiles or lower powder charges.
The initial recoil should have nothing to do with the recoil spring or the gas system. The initial acceleration of the projectile, and the attendant opposite reaction, takes place before the gas port is reached in the barrel, meaning the bcg is still locked in position. Nothing can be done to mitigate that recoil except to load lighter projectiles or lower powder charges.
Agreed, but the energy in the bcg still has to go somewhere, and it's still my shoulder the buffer spring is "attached" to. So on the buffer spring side of the semi auto we can at least manage how that piece of it handles the energy the bcg is carrying. In essence there are two recoil pulses that happen back-to-back very quickly.
And yep, only so much can be done on the cycling side of the house, but getting it to soften as much as possible while still doing a good cycle is about the end of tuning in that area.
I'm using H1 carbine buffer/spring. That seems too light for a std 300 with a large 120 gas port.
Here's why I think my issue is on buffer-spring side. As I mentioned, initially the gas block was misaligned, it was barely cycling w/ 1 in 4 fail. So I was very close to being bolt action at that point, and at that time there was very little kick, I kinda thought "ah, this is cool, it's very ez on the shoulder". But after fixing the gas block alignment is when the mule kicking started.
That sure sounds like it is over-gassed to me. Get one of these? https://blackrivertactical.com/WP/Adjustable-Gas-Drive-c6464009
So the tubes are like adj gas block?
They suggest tube hole one size bigger than barrel port.
Are you suggesting just using tube that is smaller than barrel 120 ? Their largest is a 76.
The GM barrel folks don't even suggest using adj gas block for their carbine 16" that has huge 120 port. Perhaps they should. One review there mentions having issue with adj gas block and simply went back to std block.
For supersonic ammo only, the gas port can be reduced with an EZTUNE gas tube.
https://blackrivertactical.com/WP/BRT-EZTUNE-Gas-Tube-Configurable-Carbine-p103167251
Just select "normal" for the tune and "300BLK super only" for the ammo, along with all the other obvious questions.
We'll select the best port size from there.
More info here (https://www.m4carbine.net/showthread.php?218722-BRT-EZTUNE-Gas-Tubes):
https://www.m4carbine.net/showthread.php?218722-BRT-EZTUNE-Gas-Tubes
The initial recoil should have nothing to do with the recoil spring or the gas system. The initial acceleration of the projectile, and the attendant opposite reaction, takes place before the gas port is reached in the barrel, meaning the bcg is still locked in position. Nothing can be done to mitigate that recoil except to load lighter projectiles or lower powder charges.
The rifle barely moves before the carrier is accelerated rearward.
https://www.youtube.com/watch?v=gD7pd03L43k
The rifle barely moves before the carrier is accelerated rearward.
https://www.youtube.com/watch?v=gD7pd03L43k
True.
There's a lot of energy being put into the BCG, and it has to go somewhere. Ideally the BCG should not slam into the back of the buffer tube or compress a spring into bind. If all the BCG energy goes into the spring (with a little heat) and it returns BCG back to battery, that's ideal. If the BCG has more energy than the spring can absorb then there's gonna be one of those inelastic collisions which will feel like a hard kick depending on how much extra energy the BCG is carrying beyond total spring compression.
With an over gassed system we can still fine tune the buffer weight and spring to handle that BCG energy, but it will not eliminate the extra energy from being over gassed.
My 300 is definitely over gassed (too much energy transferred to the BCG). How do we know? Because with a std carbine buffer & spring the BCG is slamming the back of the buffer tube.
To fine tune the energy there is no other way, you need to adjust how much gas energy reaches the BCG.
To changes the energy dissipation profile we can turn to buffer weight and spring K factor.
Tuning the gas is the best way.
I will try an H3 buffer weight just to see if that removes the impact force. And after that perhaps a heavier spring. After that (as needed) I will look at gas tube and gas block.
I agree that it’s almost impossible to overgas a 16” .300bo.
I do think an H3 buffer is a good start, then either a stock upgrade or a good recoil pad like a Limbsaver.
On my 16” carbine sys. 300bo I mainly run an H3/std. spring for supers and switch to a std. weight 3oz buffer for subs.
A recoil reducing stock like a Fab Defense may help as well.
I’ll admit I’m a wimp, I can shoot ARs & AKs with good aftermarket stocks all day but switching over to a surplus rifle with a metal buttplate like a Mauser or an SKS will bruise me after a few rounds without a slip on pad. An unpadded M4 stock is almost as bad. Even the $10 no name M4 rubber pads are a welcome upgrade.
I agree that it’s almost impossible to overgas a 16” .300bo.
I do think an H3 buffer is a good start, then either a stock upgrade or a good recoil pad like a Limbsaver.
On my 16” carbine sys. 300bo I mainly run an H3/std. spring for supers and switch to a std. weight 3oz buffer for subs.
A recoil reducing stock like a Fab Defense may help as well.
I’ll admit I’m a wimp, I can shoot ARs & AKs with good aftermarket stocks all day but switching over to a surplus rifle with a metal buttplate like a Mauser or an SKS will bruise me after a few rounds without a slip on pad. An unpadded M4 stock is almost as bad. Even the $10 no name M4 rubber pads are a welcome upgrade.
I think this is false. With my block misaligned it was still firing ok w/ very little recoil, but 1 in 4 would fail to pickup a new round. The misalignment was making it undergassed, but right on borderline of being ok.
At least on my M27 16", a 120 car gas port is way big for std ammo.
bamashooter
02-02-21, 07:33
Just a FYI for the inexperienced shooters. Regarding "bruising, harshness, etc to the shoulder area, much of this can be eliminated or minimized by pulling the buttstock into the body with firmness. With appropriate firmness, the energy (recoil) is more of a push / shove than it is a hammering / pounding. Observing a "light" grasp of handguns and long guns is not infrequent and the results, ranging from poor marksmanship to discouragement, is all to apparent and predictable.
Supersonic is towards the higher end when subsonic needs to function. It can be reduced a bit for only supersonic, but not that much.
300 port size cannot be compared to 5.56, and piston cannot be compared to DI. The 300 has an enormous increase of bore area for the gas to expand into vs a 5.56 bore.
Its not that I doubt you when you say that 16” carbine gas can’t be overgassed, so much as I just don’t know much about 300 Whisper/AAC/BLK. Sig, among others, sell 9” barrels with carbine gas. If those run (an assumption), then would not a 16” barrel be overgassed with the same port size?
I’ve been doing a little internet research lately about 300AAC, and I’ve learned that some people expect a gun to cycle subs unsuppressed (Why?). I would expect that to result in an overgassed gun. I don’t know that; I’m still trying to figure this cartridge out.
That must be a piston. It’s not even close, 14.5" carbine is not reliable with all ammo.
Suppressed or not doesn’t have a very big spread of function with subsonic. Not much juice to squeeze there, and some people don’t want the chance oft putting the wrong mag in for HD and have the gun choke.
Todd is right on with all points.
DI should be pistol length up to 14.5".
Subs are such low pressure, that adding a suppressor doesn't change much.
That must be a piston. It’s not even close, 14.5" carbine is not reliable with all ammo.
Suppressed or not doesn’t have a very big spread of function with subsonic. Not much juice to squeeze there, and some people don’t want the chance oft putting the wrong mag in for HD and have the gun choke.
O.P. did you check for gas key contact on the lower?
O.P. did you check for gas key contact on the lower?
Not yet. But wouldn't that too result in light cycling?
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?
https://external-content.duckduckgo.com/iu/?u=https%3A%2F%2Fmedia.tenor.com%2Fimages%2Ff33612f6107e4d590ab0833edb5c77f8%2Ftenor.gif&f=1&nofb=1
I've got two 300 Black Out ARs, one is a 7.5" and the other is 16". Standard carbine springs in both. To me there is only a slightly noticeable increase in felt recoil over the .223/5.56 ARs I have. Essentially, both calibers produce about the same muzzle energy with supersonic rounds. It really shouldn't be kicking like a mule. Felt recoil can be amplified when shooting from a bench rest too. A heavier buffer or spring may cause malfunctions, but you can try that. I doubt you will notice any difference in recoil tho.
I've got two 300 Black Out ARs, one is a 7.5" and the other is 16". Standard carbine springs in both. To me there is only a slightly noticeable increase in felt recoil over the .223/5.56 ARs I have. Essentially, both calibers produce about the same muzzle energy with supersonic rounds. It really shouldn't be kicking like a mule. Felt recoil can be amplified when shooting from a bench rest too. A heavier buffer or spring may cause malfunctions, but you can try that. I doubt you will notice any difference in recoil tho.
What gas port size in those barrels? Using std mil-spec gas tubes and blocks?
Not yet. But wouldn't that too result in light cycling?
No, it results in hard recoil, malfunctions, broken carrier key screws, ans sometimes a broken lower.
I'm not just throwing stuff at the wall hoping something will stick.
No, it results in hard recoil, malfunctions, broken carrier key screws, ans sometimes a broken lower.
I'm not just throwing stuff at the wall hoping something will stick.
The last time I took out BCG on that rifle I did not see any odd marks. But as I mentioned, will check it again.
Look on the lower.
Yep, I looked for marks throughout, no marks.
The mark will be on the lower receiver, right above the buffer. Sometimes it's a distinctive mark, sometimes it's just a slight difference in the anodizing.
What gas port size in those barrels? Using std mil-spec gas tubes and blocks?
I don't know. Whatever came with them.
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