Some buffer questions

[KC_Joe]

I picked up a couple flat wire buffer springs from Armaspec recently. When installing, I noticed the factory spring sat right against the head of the buffer, while the new springs sat "at the top of the body" and stopped where the body opens up a little before turning into the head of the buffer (I feel like this description stinks)......anyhow do you think this difference would cause any cycling or function issues? In my mind the BCG might not travel into the buffer tube as far, but I'm not sure.

Additionally, I've been reading and searching for info about buffer weight. My Grendel ejects nicely, around 4:00, but feels like it slaps open when fired. Wondering about an Odin Works adjustable buffer to play with buffer weight, but also wonder if it's even worth messing with since ejection is good?

Thanks!

[Klem]

KC,

Are you sure that flat spring can't be worked with a bit of effort to where it sits properly against the lip of the buffer? A spiral spring should be able to expand laterally as well as longitudinally. It should sit up against the lip, not the collar. The collar is designed to center the buffer and remove lateral slack.

Finding the best spring and buffer system for the length of barrel, gas system length and gas port diameter is usually done for you at the factory. As soon as you start swapping out for after market or building your own you run the risk of engineering an inefficient system. Best to get the heaviest buffer that will lock back on last round. Heaviest buffer will make for smoother cycling, especially with short barrels where early unlocking is common. The heavier the buffer the more it delays unlocking. Rather than faff around with springs and buffers you could get an adjustable gas block or adjustable carrier. Put your heaviest buffer in and slowly open up the gas until it locks back on last round. A little further for reliability and don't change it unless using a suppressor or different ammo.

[KC_Joe]

Much appreciated

[montana]

There is a lot of misunderstanding about buffer weights.. Heavier buffers effect on dwell time or lock time (the amount of time the bolt bolt takes to unlock) is insignificant..

What heavier buffers do is slow the carrier's velocity..After the bolt unlocks, it is the buffer's weight that will have an effect on the residual pressure, not dwell or lock time..
Excessive carrier velocity can be improved in an over gassed system with heavier buffers, but they can also have negative effects such as lower gas ring life, increased perceived recoil and bent firing pin retainer pins..

It is always (best) to mitigate the gas to the rifles system if possible..

Computer graphs of tests done by SilencrCo shows the lock time and carrier velocity during a high speed camera test using different buffer weights in an M4 rifle suppressed and un-suppressed.. The test proved Colts finding back in the 1960's when they switched the not so effective Edgewater ring springs buffer spring guide to the new 3 times heavier buffer developed by Colt engineer Foster Sturtevant, to counter the higher port pressure created by the slower burning WC846 ball powder..

https://www.youtube.com/watch?v=OMXd8nzE5LQ

[Klem]

[quote=montana]

What heavier buffers do is slow the carrier's velocity..After the bolt unlocks, it is the buffer's weight that will have an effect on the residual pressure, not dwell or lock time..

Montana,

That does not makes sense to me. I think we agree that the bolt cannot unlock without the carrier having moved - this is integral to the design. How then does the weight of the buffer only have an effect after it has moved enough to unlock?

[montana]

The port pressures are in thousands of pounds..A few ounces more in buffer weight is not going to have much effect on lock time..

For example, the original port pressure using the original IMR 4475 powder was 14,400 PSI.. When they switched to WC846 ball powder, the port pressure increased to 15,400 PSI..This is the force that unlocks the bolt..The actual dwell time is the point between the gas port and the end of the barrel when the gas system is charged..All things being equal (gas port /size/port location, remaining the same) the residual pressure was much higher with the ball powder than the original IMR powder, hence the carrier velocity increase and cycle rate problems..

Lock time is effected by the cam track design and port pressure..Once the bolt unlocks, the residual pressure is vented out the ejection port..The higher the port pressure, the higher the residual pressure.. Once the bolt unlocks, the carrier velocity is affected by the residual pressure and carrier weight does become a factor..

As Colt learned in the 1960's and the SilencerCo high speed video graphs revealed, the buffer weights effect on lock time was insignificant, even suppressed.. Residual pressure / carrier velocity is effected by buffer weight..

When LMT designed their enhanced bolt carrier for shorter barreled gas systems, they changed the bolt cam track to increase the lock time so residual pressures would have more time to dissipate after the bullet left the barrel... It worked very well.. The reason the military rejected the enhanced bolt carrier for shorter barreled rifles was because it was not reliable with rifle length gas systems (too low of residual pressure to reliably cycle the rifle length gas system) and they didn't want to have two types of carriers in the supply system..

When the bolt unlocks, the extractor lifts completely off the case rim and is dependent on the same residual pressure to hold the case against the face of the bolt until the extractor lowers back down to allow extraction....

A good example of residual pressure would be an air hose..When an air hose is plugged into a compressor, the air hose is charged..When you unhook the air hose, the air escaping from the hose is residual pressure..

Balancing the residual pressure is what determines a reliable gas system and there are different ways to approach this..Which one is optimum is what creates a great many debates on gun forums..

[Klem]

Montana,

I get your ideas: residual pressure in hoses/barrels (associated with dwell time), LMT's different cam track and the politics behind it on AR15.com.

So, you are saying heavier buffers do little to smooth and slow unlocking?

[montana]

I don't know what you mean by smooth, but yes, heavier buffers effect on the bolt unlocking/opening cycle is negligible..

I first read about this in the Black Rifle book Page 200-201..Colts newer buffer was nearly 3 times heavier than the older Edge Water buffer and its effect was insignificant on the bolt-opening cycle..

The SilencerCo high speed camera/computer graphs verified this..

https://youtu.be/OMXd8nzE5LQ?si=IWmYvEhJeZ3O5XFC&t=760

[grayfox]

Having a negligible effect seems reasonable, at least for the unlocking: as I understand it, unlocking is primarily a rotational motion/operation, which some extra mass in the buffer would not have any impact on. As for rearward motion, seems possible that an increase of ounces compared with the thousands ksi pressure acting upon it (the cross sectional area being the same) so the force/acceleration, F=m*a, might get slowed a bit by having to accelerate a heavier mass... but it could also be a negligible impact. I haven't run any numbers personally, but it doesn't defy logic either.

edit to add.
I went back to listen to the video, it started for me (in the link) about 14:00 into the run. His discussion revealed a couple things that might have a bearing on this discussion here, as what I would call clarifications.
1. His discussion of bolts and buffers in this part of the vid seems to revolve around shooting suppressed/unsuppr., as well as he mentions that some might be using "boutique" really heavy buffers (beyond the H1-H3 range) -- of which boutiques I don't have any knowledge-- as compared to H1-H3 buffers. In discussing bolt movement, he says a heavier buffer (implying mostly the H1-H3 range) will slow down buffer movement and make it run "smoother" - a rather unscientific term imo, but probably referring to a more or less lack of "crashing" into the back of the buffer track at the end of the rearward movement... He does also say that there is a delay in buffer opening, but it is of the order of 0.5-1.0 millisec, which to him was a negligible timeframe.
2. I didn't see parts where any graphics of bolt motion or high-speed vid segments, so I'll leave that discussion to others. Maybe those were at a different point in the vid.

This all may or may not impact our discussion here, but for someone shooting only unsuppressed, and thinking of whether to use carbine, H1, 2, or 3, the "slower opening" may not be perceptible but a slower buffer velocity and "not-so-crashing-into" the far back travel stop, may be perceptible, and useful. Any "slowing" of the opening cycle is probably not detectable to the avg user.

[LRRPF52]

The main reason for increasing buffer weight is to counter carrier-bounce on FULL AUTO, depending on barrel weight.

The primary vector for controlling cyclic rate is the port location and aperture diameter, relative to propellant volume and bore volume, propellant burn rate, and projectile resistance.

The M4A1 SOCOM “upgrade” to the heavy barrel brought with it the H2 buffer, for example. The 727 barrel profile guns ran fine before that with standard or H buffers, unsuppressed.

When shooting and testing different buffer weights in 6.5 Grendel, I haven’t seen much perceivable performance difference in the cyclic rate even when I put multiple 20” rifles next to each other with different buffer weights.

I have noticed very perceivable cyclic rate behavior with different gas port or adjustable gas settings, as well as spring weights.

I was surprised to experience one of the smoothest AR-15 cyclic rates ever with 12” CLGS with the tiny little PDW back-end, short PDW RET, tiny buffer, and stiff action spring.

[montana]

TACOM Understanding Extractor Lift in the M16 Family of Weapons test..https://www.slideserve.com/mead/may-2003

This test explains the importance of residual pressure in the extraction process..I have posted this on this forum before..

[SDW]

If you're going to try a flat-wire spring, maybe you should get one from the guy who (I think) invented the idea. David Tubb. He no doubt has done the most testing with them. This spring works in both Rifle and Carbine buffer systems, and it fits properly on both style buffers:

https://www.davidtubb.com/ar15-bufferspring


Having said that though, I'll admit I used one for a while but I found that it wouldn't allow some of my lighter loaded .223 ammo to cycle fully. So it made the most sense just to swap back to a standard spring. Might have been when I had it in my Rifle lower with the rifle buffer.

Haven't tried this spring with any of my Grendels, so I can't say how it works there.

ETA: After thinking about it, in this situation it might simply be best to start out running the rifle with a standard carbine spring and standard carbine (no "H" anything) buffer. See if it runs okay, meaning reliably, with that before experimenting with 'better' parts that might affect felt recoil, etc. it should work fine with standard parts. I believe Klem touched on this earlier. Make sure the rifle works with standard parts. Then maybe start playing with heavier buffers if you want.

[montana]

Having a negligible effect seems reasonable, at least for the unlocking: as I understand it, unlocking is primarily a rotational motion/operation, which some extra mass in the buffer would not have any impact on. As for rearward motion, seems possible that an increase of ounces compared with the thousands ksi pressure acting upon it (the cross sectional area being the same) so the force/acceleration, F=m*a, might get slowed a bit by having to accelerate a heavier mass... but it could also be a negligible impact. I haven't run any numbers personally, but it doesn't defy logic either.

edit to add.
I went back to listen to the video, it started for me (in the link) about 14:00 into the run. His discussion revealed a couple things that might have a bearing on this discussion here, as what I would call clarifications.
1. His discussion of bolts and buffers in this part of the vid seems to revolve around shooting suppressed/unsuppr., as well as he mentions that some might be using "boutique" really heavy buffers (beyond the H1-H3 range) -- of which boutiques I don't have any knowledge-- as compared to H1-H3 buffers. In discussing bolt movement, he says a heavier buffer (implying mostly the H1-H3 range) will slow down buffer movement and make it run "smoother" - a rather unscientific term imo, but probably referring to a more or less lack of "crashing" into the back of the buffer track at the end of the rearward movement... He does also say that there is a delay in buffer opening, but it is of the order of 0.5-1.0 millisec, which to him was a negligible timeframe.
2. I didn't see parts where any graphics of bolt motion or high-speed vid segments, so I'll leave that discussion to others. Maybe those were at a different point in the vid.

This all may or may not impact our discussion here, but for someone shooting only unsuppressed, and thinking of whether to use carbine, H1, 2, or 3, the "slower opening" may not be perceptible but a slower buffer velocity and "not-so-crashing-into" the far back travel stop, may be perceptible, and useful. Any "slowing" of the opening cycle is probably not detectable to the avg user.

Go back and watch the video..The graphs are plainly shown and the time the bolt unlocks and the velocity/time frame of the carriers..In one of the graphs, the lighter buffer actual unlocked later than some of the heavier ones..The point was the difference in the unlocking time frame using different buffer weight is insignificant, which was my point from the start..Heavier buffers do slow the carrier velocity consistently.

52 is correct that the heavier buffers were used to prevent bolt/carrier bounce..The heavier the barrel the more carrier bounce occurs..

What I consistently here/read is that many people think the heavier buffers will delay the bolt from unlocking and improve dwell time which is not true..

Heavier recoil springs and buffers will also slow the carrier velocity which will prevent feeding and recoil problems ( it allows more time for the magazine spring to push the next cartridge in the magazine in the proper position for the carrier to grab) if the rifle is over gassed..

I have always advocated mitigating the gas if possible, but like I stated earlier it is a topic with many different opinions....

[KC_Joe]

Really appreciate the discussion here.

To SDW's point, this rifle runs well with its factory parts (carbine buffer and spring). It does have an adjustable gas block, which I've experimented with a bit, but maybe some additional adjustments through its whole range might be worthwhile.

[SDW]

Really appreciate the discussion here.

To SDW's point, this rifle runs well with its factory parts (carbine buffer and spring). It does have an adjustable gas block, which I've experimented with a bit, but maybe some additional adjustments through its whole range might be worthwhile.

The reason I mentioned it is because in your other thread about receiving your upper you said you are/were not getting full lock-back sometimes. If that's the case then your rifle might be a little under-gassed for various possible reasons, or it doesn't like the heavier buffer and 'aftermarket' spring, or a combo of both.

And of course if it is under gassed, IMHO there's no point in experimenting with the gas adjustments on the gas block. You'd want to open it up all the way and get all available pressure coming up through the barrel's gas port. 'Cause at the risk of stating the obvious, AGBs can only reduce gas pressure. They can't magically amplify it.

[Zeneffect]

Just a thought about port pressure...

15k-17k psi is seen on the barrel side of the port, what does the gas tube see? There is a pressure reduction when you have the smaller orifice/gas port and it seems everyone is skipping that calculation? I would think 15kpsi would rupture the gas tube near instantly wouldn't it? Pretty sure I've blown up stronger stuff with less pressure so the tube seeing 15k is questionable to me.

Not to say this has any bearing on the unlock time... but also the stated .5-1ms extra dwell in the scale of time we are looking at is quite a decent amount for the pressure to drop. Extra 1% or so of additional time scales out on the pressure side to thousands of psi of chamber/gas pressure

All that being said, I run a super42 spring and h2 buffer with no adjustable gas block on all my carbines. Cyclic rate is perceivably slower, and it just flat out runs without issues so I don't touch the setup. Sometimes I wonder if I went the opposite direction what that would be like (light buffer, spring, carrier, minimal gas)

[LRRPF52]

I think the happy window of operation for the expansion chamber inside the carrier is 2000-2200psi with a Mil-Std M16 carrier weight.

[montana]

You would be correct about the reduction of pressure entering the gas key..The barrel port pressures were an unknown in the early days as Colt, Stoner/Armalite or Remington never had a way to measure them..It was Springfield armory who first invented a way to measure port pressure..The lack of port pressure specs is what caused the problems when ball powder was first accepted for use..The cycle rate and fouling were the main concern when they first were considering a switch to ball powder..Colt's very capable engineer Foster Sturtevant made a very bad claim he would later regret when he first stated the extra port pressure would make the M16 more reliable.. Barrel port pressure for ball powder could accede 17500 lbs while staying well within the safe chamber pressure spec..When shorter barrels and gas port locations come into play, the burn rate changes drastically, creating a much higher residual pressure curve..

In one of the graphs, the lightest buffer had a longer lock time than the heavier ones..My main point is it is the residual pressure that is effected by buffer weight and spring tension, not the bolt un-locking cycle..Even Stoners claim that the higher port pressures with ball powder caused the bolt to unlock prematurely (as the case was still expanded to the chamber wall) that caused the catastrophic stuck cases, ripped off rim malfunction has been dis-proven..It was the lax case hardness in pitted chambers that caused these extraction problems..

[grayfox]

As a matter of fluid flow, gas pressure does not reduce until there is flow through the tube. Instantaneously as the bullet passes the port, the pressure, 15, 16, 22k, whatever, is felt throughout the barrel/tube volume due to the gas laws, but then pressure down the tube begins to drop due to head losses during the fluid flow. Of course the source pressure at the port is also dropping due to further bullet movement down the rest of the barrel.

Think I’d agree with Montana that residual pressure, what is available to move the bolt and buffer coming down the gas tube after the bullet passes, is affected by buffer weight and spring force, those are the opposing forces that will move the bolt etc and cycle them.

[Happy2Shoot]

I learned a few things from Lantac.

1 The majority of the gas comes out before the BCG moves.

2 No gas comes out of the chamber after the BCG moves.

Therefore, I no longer believe extra mass buffers help with educing gas to the face.

https://www.lantac-usa.com/e-bcgwhitepaper