Originally Posted By Bebop_941:
Standard buffer and spring will always produce less felt recoil in a properly gassed system.

Originally Posted By Raidersgone:


Thanks, I'm going to start with RCA's adjustable gas key. Trying to tame that impulse. I've read heavier buffer produces more due to mass at the rearward cycle. But, actually read the opposite also. Kind of confusing.

Originally Posted By Raidersgone:


Thanks, I'm going to start with RCA's adjustable gas key. Trying to tame that impulse. I've read heavier buffer produces more due to mass at the rearward cycle. But, actually read the opposite also. Kind of confusing.

Originally Posted By PreacherOfGadget:


A cycling system (BCG+Buffer) with more mass will reduce the acceleration in all cases.  When the action starts firing rearward after a shot, more mass means the cycling system accelerates rearward more slowly.
F= mass * acceleration

When the cycling system reaches the rear of its cycle, any remaining energy that hasn't been absorbed by the buffer spring is transferred to the rear of the buffer tube and into the shooter's shoulder as the buffer+BCG swiftly decelerate and stop.  More mass, instead of making the BCG decelerate at a lower rate (as an opposing force (rear of buffer tube) is stopping the system), dumps more energy into the end of the buffer tube at the rear of the cycle: increased impulse and felt recoil.

Energy = 1/2 * mass * (velocity^2).
Force = mass * acceleration.
Momentum =  mass * velocity.
Impulse = Force  * time = change in momentum.

Those are the formulas that govern this movement.  You'll notice the time factor above.  Increasing this number also helps.  If you're really concerned about impulse at end of cycle, there's also various multi-spring buffer systems and hydraulic buffers that don't alter the overall system mass much, but they do allow additional compression at higher resistance at the rear of the cycle.  (These same systems typically also reduce or eliminate bolt bounce on the forward stroke.)  This increases the time in the impulse formula above, reducing the impulse but not reducing the overall energy or momentum.  

This approach also ensures the system has enough energy to extract and to chamber new rounds, but reduces the rate that energy is dumped into the shooter's shoulder.  

I've discovered I like Kynshot hydraulic buffers.  (This revelation came from working 9mm direct blowback ARs, which have much worse impulse at the rear of cycle due to their heavy reciprocating masses.)  Kynshot buffers are not cheap, but they do exactly what they're supposed to, and if they break (very rare), I hear almost exclusively good things about Kynshot customer service and replacement.  Kynshot isn't the only specialized buffer game in town, but they've got a strong track record.

Work the adjustable gas block first.  Not that you should go this far, but a system tuned to the ragged edge could run on just enough energy to chamber a new round from a full mag in a dirty gun.  If the system gets too light, too under-springed, or too under-powered (under-gassed), you'll lose last-round bolt lock back and potentially get chambering issues.

Originally Posted By Raidersgone:


Good info. Since this is a budget end rifle Kynshot is more than I want to invest. I'm thinking adjust the gas and go stiffer spring with standard 3.0 oz buffer. SprinCo recommends this option, which I have a couple of theirs, a hot red/white and a blue.

Originally Posted By Bebop_941:


If you plan on regulating gas to a correct level, you don't have to change the buffer or spring.  Keep everything standard and just tune the gas accordingly.  A stiffer recoil spring will just increase your return to battery speed and is unnecessary if you're already tuning gas.  Just my $0.02.

Originally Posted By TonyAngel:
What are you after? A soft shooting rifle or a reliable rifle? The more gas required to run your rifle, the more reliable it will be.

If you tune your rifle to shoot softly with a standard carbine buffer and spring, it will be much more sensitive to differences in ammunition, changes in the environment and getting dirty. If you want it to run reliably, tune the gas to cycle an H, or preferably an H2 buffer with a standard spring or maybe a bit heavier.

To say that increasing buffer weight slows the bolt speed is a bit misleading. Yes, slower bolt velocity is a side effect of more buffer weight, if nothing else has changed, but what has really happened with the increase in buffer weight is that the closed bolt lock time has increased. Since the bolt takes longer to unlock, less pressure is acting on the carrier by the time it starts moving so you get less velocity.

Originally Posted By Raidersgone:

Thanks. I'm after both. As soft and reliable as I can get with carbine gas length 16" bbl. I was at 1:00 eject with standards combo. I went H2 and stiffer blue spring got me 2:30-3:00. I'm going adjustable gas and try to tune what would be the smoothest combo and most reliable in all weather.

Originally Posted By MS556:
I have a Lilja M4 Navy SEAL 16" barrel.  By definition it uses a carbine gas system.  It also has a hoggish .080" port.  I questioned whether that was mil-spec per NSWC Crane.  Carson Lilja told me it was and has never changed.  Presumably, they wanted the Recce to reliably cycle under any possible operating conditions.  Long term component life was less of a concern.

Well, this is a precision build, so I toned things down by running an H2 buffer and an adjustable gas block.  I set the block to cycle reliably with my lower velocity match ammo, and locked it.  I should be able to run anything now except very weak bulk imported stuff, which that build is not likely to see.  Seems pleasant to shoot.

Originally Posted By Ops:
Bushmaster SL 16", carbine gas system, H buffer.  The heavier buffer really smoothed it out..

Recently replaced the bolt, cam pin, and used a Wolff buffer spring.   Ejects to 4:00.  Closes like a bank vault..

Don't overthink it.

Originally Posted By JoeDevola:
I use H2's all around.  Everything's smoother.

Originally Posted By GHPorter:

This is probably the best advice.

“Overgassed” gets thrown around a lot, but from a reliability perspective, more gas is better.  More gas means more energy provided to the reciprocating parts, which ensures there’s enough energy to extract the empty case, eject it, and cycle far enough back to load the next round.  Having more than enough gas from a middle-of-the-road round means that wimpier rounds will still work.

When there’s more than enough gas, the reciprocating parts can go faster than they need to, which feels rougher.  You will never get “too much gas for the system” because the bolt carrier/bolt system actually meters the gas; with hotter rounds you’ll have more gas vented out of the carrier through the ejection port than with milder rounds.  By the time this happens, the carrier has started to move and has enough energy to cycle reasonable rounds.

So the way to moderate the extra rearward speed of the reciprocating parts is to give them a bit more resistance to push against, like a heavier buffer.  A standard carbine buffer weighs about 3oz, while an H2 weighs about 4.6 oz - about 50% more.  Further, buffers have reciprocating weights inside them.  A carbine buffer has two steel weights that can slide a bit, which helps spread out the rearward - AND forward - movement over a longer time.  The H2 buffer changes those steel weights for two tungsten weights, so the inertia resisting movement in both directions is much higher, and that helps both resist overly fast carrier movement backward AND forward, which helps reduce or prevent bolt bounce.

So “overgassed” should mean so much extra gas that the metering system can’t moderate the rearward speed of the carrier and it slams very hard into the end of the receiver extension tube.  This symptom can be checked for by looking for damage to the rubber bumper on the end of the buffer.  Unfortunately, the term is typically used for a situation where one’s chosen ammo makes the carrier move quickly and maybe there’s a lot of gas coming out of the ejection port.  I think of this the same way I think of “the chart”; it’s something that is useful in a very specific situation, like when the gun isn’t consistently extracting and ejecting, or it’s battering parts.  UNLESS the gun isn’t working reliably, IGNORE “the chart”.  And unless the gun is battering itself and the shooter where actual damage might happen, it’s not mechanically overgassed.

OK off the soap box now.  It’s safe to come out!

Originally Posted By Raidersgone:

Thanks, good explanation. Seems some differ on using lighter or heavier buffer for smoothing felt recoil impulse.

Originally Posted By bluedog82:
Almost all 16” carbine gassed guns are going to be overgassed. The 6920 is one of them, and comes standard with an H buffer. It could easily go to an H2 , as that is what the Block 2 and Mk18 both use with less dwell time. Swapping in an H2 will make the recoil feel slower/smoother.

Originally Posted By TheQuadfather:



A 6920 is by no means overgassed.  It will reliably run with ANY commonly available buffer from Car-H6.  As will any upper because the gas system is largely unrelated to the buffer.  

I did a lot of testing with different buffers and springs with mid and carbine gas barrels.  The 6920 barrel with H buffer and stock spring was unanimously favored over the BCM 16" with any buffer because the Colt barrel is gassed more appropriately 5.56. The shooters reported a softer, quicker recoil impulse with less dot movement which allowed for more rapid and precise splits.  These were very competent competitive shooters who were also firearms instructors.  

Gas systems and buffers are misunderstood by most.  

Originally Posted By BrownellsGT_Justin:
if the gas is truly “right” (just enough to run and lock back), the lightest reliable setup usually gives the least felt recoil. Heavier buffers/springs are most helpful when you’re over-gassed; they don’t reduce the total recoil impulse, they just slow/spread the action’s movement so it feels less sharp.

Originally Posted By bluedog82:
Almost all 16” carbine gassed guns are going to be overgassed. The 6920 is one of them, and comes standard with an H buffer. It could easily go to an H2 , as that is what the Block 2 and Mk18 both use with less dwell time. Swapping in an H2 will make the recoil feel slower/smoother.

Originally Posted By TonyAngel:
Ejection pattern is determined by a few things. The most notable are the ejector/spring, the extractor/spring and bolt velocity. Chasing an ejection pattern gets you nothing.

Yes, the ejection pattern can be an indication of being over or under gassed, but it isn't the end all test of a rifle's reliability.

If we're talking about the proverbial SHTF, gotta work rifle that everyone likes to think that they have, what you should be seeking is the utmost  in reliability; not a rig that shoots as soft as it possibly can.

The way that I think of it is that each rifle has, what I've come to call, an operational window. This window represents the environment within which the rifle will run as it should. The bigger the window, the broader the circumstances within which the rifle will run. What I mean by environmental circumstances is the variables typically encountered. Available ammunition, weather, availability of lube, how dirty the rifle is, etc.

In my experience, generally speaking, a rig tuned to run on a higher volume of gas will have a bigger operational window than a rig tuned to run on a lower volume of gas. I think that taking a slightly overgassed rig and tuning it with a heavy H2 or H3 buffer will net you a more reliable setup than turning the gas down so that it'll run soft on a standard buffer and spring.

Originally Posted By tet493:
@Raidersgone
Dude just pick up an H Buffer and Sprinco recoil spring. No need to make things complicated. If it’s super over gassed(PSA) get the blue spring. If it’s less over gassed get the white-red. You could just but the three springs and see how it ejects with each.

I am using the white-red in my 6920 with an H buffer. I may put a carbine buffer in for weaker/plinker ammo.

416s are more reliable because they are more aggressively gassed with a much stronger buffer spring. Use the gas to your advantage.

Originally Posted By Raidersgone:

Thanks, this was a not PSA brand. My over gassed carbine gassed barrel ended up as a learning and experimental project. As I posted in the thread, I began trying different buffers and spring combos you listed. Landed on a standard spring and 4.0 oz. tungsten powder buffer with adjustable gas key, which got this barrel to the results I was curious about.

Originally Posted By RD20:
@bfoosh06 how reliable has the adjustable key been for you?

Originally Posted By RD20:
@bfoosh06 how reliable has the adjustable key been for you?

Originally Posted By bluedog82:
Almost all 16” carbine gassed guns are going to be overgassed. The 6920 is one of them, and comes standard with an H buffer. It could easily go to an H2 , as that is what the Block 2 and Mk18 both use with less dwell time. Swapping in an H2 will make the recoil feel slower/smoother.

Originally Posted By Raidersgone:
or, will the Standard buffer and spring produce less recoil impulse when gassed properly?

Originally Posted By TonyAngel:


How do you define properly gassed? A rifle running a standard buffer and spring, with an appropriate closed bolt lock time is properly gassed. A rifle running an H2 buffer with a springco white/hot spring with an appropriate closed bolt lock time is also properly gassed.

If you are looking for the least amount of felt recoil, then a gas port that allows an amount of gas through the system sufficient to cycle the rifle while only requiring a standard buffer and spring will do that; but it doesn't necessarily meant that it will be the most reliable setup. This often leads to a rifle that feels spongy and does not snap back on target. Tuning for light weight also means that the system will be more sensitive to environmental changes like temperature and brand of ammo.

Originally Posted By Bebop_941:


Can you explain how the part above  in red can result in the part above in blue?  Not trying to pick a fight but you've mentioned these points several times and I'm just trying to understand your claim.

Originally Posted By RD20:
@Raidersgone just FYI; I placed an order for two adjustable keys, and the next day an employee called to ask what the intended use was. I told him I wanted them to be reliable as everything else on the gun, which led him to canceling my order.
I didn't ask to cancel the order, but rather he talked me into it.

Originally Posted By TonyAngel:


Ok. The term, or expression, "properly gassed" or "over gassed" refers to a condition or state of the firearm. If you take an 11.5" barrel with a .075 or larger gas port and run it with a standard buffer and spring, you will likely experience things like excessive bolt velocity, stuck cases or even torn case heads. It is over gassed. You take that same rig and drop an H2 or H3 buffer into it and now it runs right. No more excessive bolt velocity, stuck cases or torn case heads. The rig is now properly gassed.

In the above example, you ask yourself what has changed? Of course, the obvious thing is that we added a couple of ounces mass; but, do you really think that adding that little bit weight was able to slow that carrier down? I mean, the 5.56 round generates something around 65,000 PSI of pressure.

The important thing that happened, when adding that weight, is that the closed bolt lock time was increased. The bolt stayed closed for just a few milliseconds longer allowing the pressure in the system to drop before the bolt unlocked, which resulted in the lower bolt velocity.

So, when you say that a rig is over gassed, what you're really saying is that it is suffering from an insufficient closed bolt lock time.

What I'm trying to get to is that you can have a rig that runs properly on a standard buffer and a rig that runs properly on an H2 buffer, as long as both have an appropriate closed bolt lock time and, thus, both are properly gassed.

In the real world, however, I do not think they are equivalent. If you take that rifle running a standard buffer and spring and the one gassed to run the H2 buffer, clean and lube them both, then take them both out in real use. Mud, rain, dirt, sand and run them both in that environment. Put maybe 1000 rounds through each. No cleaning. No lube. I'll bet that the rig running the standard buffer and spring will choke first.

The rig running the lighter reciprocating weight and less gas will be more susceptible to environmental influences. As it gets dirty, you're gonna start to feel the bolt carrier struggle to do its job. It will get sluggish and spongy, then it will get to a point where it will stop locking back and then it'll stop feeding.

The rig with the heavier reciprocating mass will run longer and more reliably because it's running on more gas. You will also notice less of a change in the way the rifle runs when going from say, .223 steel cased to real M193.

I'm just sharing my experiences. I've done the testing that I described above. I've been putting ARs together for over 20 years and I had my own head scratching moments.

Bottomline is that you shouldn't be tuning for the lightest possible recoil. Any AR is just a conglomeration of parts and there's no telling how they are going to interact with each other in terms of how the rifle is going to shoot.

What you should be tuning for is reliability.  Of course, much of this is wholly dependent on intended use. I aim for the utmost in reliability.

People also need to understand that spring rate has little to no effect on closed bolt lock time. Many guys will take an over gassed rifle, take note of the 1:30 ejection pattern and think, wow, I'm over gassed. Then they'll add a springco red spring, get a 3:30 ejection pattern and think, oh, I fixed it.

No, now you just have an over gassed gun with a good ejection pattern. Where springs are most helpful are in aiding chambering when the rig get filthy.

When running a standard buffer tube, a good setup is an H2 buffer with a springco white hot or blue spring.

Originally Posted By RD20:
@Raidersgone I ordered two because I thought they were super reliable items and wanted the ability to dial the gas. I wasn't trying to correct any issues I was having as there were no issues. I just thought they were pretty slick items. Besides that, I love to tinker even where tinkering isn't needed.

So, he called out of the blue and we had a short discussion. He told me if it was for a life and liberty rifle to consider not using them, probably since there were no issues that I was trying to correct.

I was pleased with his honesty.

Originally Posted By Bebop_941:



How do you feel about adjustable gas blocks?  

I would also take an adjustable block over an adjustable key.  An adjustable key directly affects the function of the expansion chamber on the BCG.  An adjustable block simulates a properly sized gas port by controlling the volume of gas sent down the gas tube.  

I can see where changing the volume of gas AT the expansion chamber could create issues vs. changing it at the gas port.