Originally Posted By bluedog82:
You’re asking if heavier buffers INCREASE wear, as opposed to a lighter buffer in the same rifle? Generally it’s the opposite, as the system is slowed down and the unlock is delayed.

Originally Posted By backbencher:
You're probably accelerating wear on the upper; .mil M4s run H2 buffers.  If H2 buffers noticeably accelerated bolt wear we'd probably see the .mil seeking a different solution, and I've not heard of a program to change buffers in the M4 platform.

Originally Posted By mace2364:


When did that happen? They used to run standard carbine buffers.

I’m legitimately asking, not trying to be a smartass, just to be clear.

Originally Posted By mace2364:
When did that happen? They used to run standard carbine buffers.

Originally Posted By mcantu:
This is from a 2010 Colt maintenance manual:

Ensure the proper buffer is used with the proper rifle. Buffers marked with "H" are used in all semi-auto only 5.56mm carbines and select fire M4 and Commando carbines. The "H2" buffer is only to be used with heavy barrel carbine barrels.

Originally Posted By bluedog82:

This is obviously not accurate and makes no sense, unless Colt is trying to say that all their HBARs have big gas ports.

Originally Posted By bluedog82:

This is obviously not accurate and makes no sense, unless Colt is trying to say that all their HBARs have big gas ports.

Originally Posted By theguymontag:


It’s due to the weight of the barrel and capability of fully automatic fire. Former Colt employee confirms the above.

https://www.youtube.com/watch?v=DYf-MLMODhA

Originally Posted By Bebop_941:


The H2 was introduced to mitigate bolt bounce with the heavier profiled SOCOM barrels.

Because the barrel has more mass, the carrier wants to bounce off the extension when it returns to battery.  This is a similar phenomenon to striking a steel anvil with a ball peen hammer - the hammer bounces off.  The heavier the profile of barrel, the more the carrier wants to bounce.  This can cause hiccups in select fire guns as the bolt bounces out of battery at the same time that the hammer falls.

Regarding gas port size, it's true that alot of people use H2 buffers to delay unlocking in over gassed guns but that was never its intended use (despite the fact that it does help).

Originally Posted By Raidersgone:
I have the LW pencil barrel. Are the barrel extensions the same for a socom profile, gov., LW, and HBAR?

Originally Posted By lysanderxiii:

What you say is only partially true:

The XM4s used a standard weight buffer and worked acceptably, but the H1 was considered optimum it terms of cost and tungsten consumption for production.  This was done to reduce the cyclic rate.

It was not the heavy barrel that was the reason for the H2 buffer, it was the return to full automatic fire.  Initial batches of the M4A1 in 1987 were found to suffer from light primer strikes (bolt bounce) during automatic fire acceptance testing, these were the with initial barrel (light) profile.  The issue was the H1 buffer did not prevent bolt bounce, but the three round burst masked the problem.  During three round burst firing you only had a stoppage if the light strike occurred during the firing of all three rounds, if the bolt bounced on the fourth round chambering, you didn't have a stoppage.  So, the observed frequency was only three-quarters the actual frequency, which was low enough to be deemed acceptable.  However, when full automatic fire was reintroduced, testing was done with three to five second bursts, and the true frequency of the light strikes was observed.

The heavy buffer was a low priority as at that time the M4A1 was not going to be general issue and there was not a problem in the M4.  So, a number of (cheaper) alternatives were investigated, using the weights from the M231, tungsten powers, lead shot, hydraulic buffers and so on as they actually did not want to increase the buffer weight too much and further reduce the cyclic rate.  Eventually, two tungsten and one steel weight was selected it only marginally impacted the cyclic rate, and was the simplest, most reliable fix.

The heavy barrel being the cause and the heavy buffer being the solution myth is due to the fact that heavy barrel was first in the M4A1, the M4A1 (even with the light barrel) had the bolt bounce problem, and the heavy buffer came out about a year afterwards and the problem went away, so many people thought the heavy barrel was the cause and the heavy buffer the reaction to the cause.  But in reality, the light barrel had the problem, too.

Originally Posted By j3_:

This just makes me wonder why the IAR with an even heavier barrel had an H3 buffer and why Colt's manual seems to elate the H through H3 to guns barrel weight. I thought the idea of the carrier getting more bounce back as the object it stuck gained mass made sense?

There used to be some videos on youtube years back catching the cycle of the carrier and the bounce when tested with different buffers. I thought it seemed unusual that for that gun when it got t the H3 weight buffer it appeared to go slightly backwards and lose some of the reduction it had achieved with the H2 used before it.

Originally Posted By Bebop_941:


I always thought it was a combination of both.



Did all of the Colt carbines that precided the M4 and used standard buffers suffer a from the same issue?  Or, was it a new issue due to a unique change in the M4 itself?

Makes sense.



I'm curious what was different about the M4 in full auto that created this problem.  Was it aways a problem dating back to the first Colt Carbines and just not well documented?

Interesting post -  the mass explaination always made sense and it's what the video above cited so I figured it was true.  

You've always been knowledgeable in what you say so I'm not doubting what you posted.  I am curious if you can shed some light on to why this became a problem when the M4s returned to full auto when several full auto carbines before the M4s operated with standard weight buffers - Thanks.

Originally Posted By lysanderxiii:

The XM177E1 and E2 were never rigorously tested.  The only serious test of the XM177/CAR was the Small Arms Weapon System (SAWS) Test which only classified malfunctions into three categories, those that could be fixed by the operator in less than 10 seconds, those that could be fixed by the operator, but took longer that 10 seconds to rectify, and those that required the weapon to go to an armorer.  If the number of light strikes was high, but the overall number of less than 10 second stoppages was low, no one would have noticed.  Then a thousand or so were sent to Vietnam and field trialed. But, detailed field reliability data was not gathered, mainly it was for opinions of its usability and likability, so you don't know what you don't know.

The other things is the light strike problem was not every magazine.   With the M4A1 it was not seen with every magazine, maybe once every fifth or sixth magazine you would see one stoppage.  Something that definitely raises a flag during acceptance testing, where you are shooting a hundred or so carbines a day, with some undergoing a 6,000 round endurance test.  This puts a serious crimp in production as the batch fails acceptance, you have to go back through production records, rule out manufacturing errors, and eventually retest the batch or ask for a waiver.  In the field, if you are shooting full auto in combat you just figure it was a bad round, cuss a bit, rack the bolt, and go back to shooting.  Besides, most shooting is done in semi-auto, where bolt bounce is a non-issue.

After 1972, the Army dropped the XM177A2 and stopped all testing, so, Colt no longer had to report how reliable the short barreled AR-15 was.  They probably knew it was marginal, but just hoped that it was good enough when the M4 was being developed.

Like I said the heavy buffer and the heavy barrel came out at the same time, in fact, the conversion kits included both, so it is a natural assumption to make, that the two were related, but, the reality is they were two parallel development tracks stemming from two different issues.

Originally Posted By Bebop_941:


Thank you for the detailed response and the time it took to post it.  Can we assume the same was true with the transitional carbines like the 653, 723 and 733?