View Full Version : Dropping buffer weight with a "tight" gas port?
Details of what I'm talking about:
Hodge Defense 14.5" mid-length barrel, gas port purportedly 0.74" or 0.75", made a little tighter for M855A1.
LMT Enhanced BCG
Ammo will be M855 (not A1), Mk262, or Mk318, but all 5.56 NATO stuff (no .223)
So the gas port is "tighter", and the LMT EBCG will take it a bit further in that direction. I IM'd Jim Hodge on Facebook and he said it might be a little much, but to try it.
So it is generally understood that increasing buffer weight will help "tame" (if you will) an over-gassed barrel. Does the reverse hold true, i.e. a strangled gas release can be assisted in function by decreasing buffer weight? The modern standard seems to be an H2 buffer. If cycling is an issue would trying an H or even carbine buffer serve to alleviate that? I guess a good indicator of a "sweet spot" would be proper cycling and then lock-back on an empty mag, correct? Yes, I know extreme cold weather could alter this, but it does with a lot of weapon functioning, not just AR's.
I only ask this because sometimes, when it comes to weapons (and AR's in particular), what you think would be obvious isn't always the case.
Lower buffer weight will allow better function with lower gas drive, but the difference is not tremendous.
Lower buffer weight will allow better function with weaker ammo, but the difference is not tremendous.
So in this case the "weaker" ammo is in fact full-pressure 5.56 NATO loads, not over-pressured M855A1. Nonetheless a "weaker" load than the gas port was designed for. Since I'll start with an H2 I have two more steps downward to play with (H then standard carbine buffer).
I know eliminating the LMT EBCG would un-complicate it, but it's NIW and I want to use the damn thing (not to mention pricey also)! I also like them so would like to find a way to make it work in this setup if possible.
Edited to say lower gas drive, either from a small gas port, weak ammo or both.
Will it run regular 5.56 with a mil-spec BCG ok?
So in this case the "weaker" ammo is in fact full-pressure 5.56 NATO loads, not over-pressured M855A1. Nonetheless a "weaker" load than the gas port was designed for. Since I'll start with an H2 I have two more steps downward to play with (H then standard carbine buffer).
I know eliminating the LMT EBCG would un-complicate it, but it's NIW and I want to use the damn thing (not to mention pricey also)! I also like them so would like to find a way to make it work in this setup if possible.
Don't know yet, brand new setup.
A 0.074 gas port is not on the small side. for a 14.5
A 0.074 gas port is not on the small side. for a 14.5
Good to know, thanks. FWIW I found an online "master list", if you will, of gas port sizes by manufacturer:
https://docs.google.com/spreadsheets/d/1tXunBDX5Gaz87BqxwNxDUlWNK9nEv-cZEQoLq2JXXrk/htmlview
Per the list above, the Hodge gas port is 0.075". The next one up is 0.076" (several manufacturers). I'm not a mathematical or ballistic engineering prodigy by any stretch of the imagination, but I guess that 0.01" difference is close enough to be essentially the same.
I can't recall where I read it but another source said Hodge used a 0.074" gas port. Looking at that list and with the other info, a 0.74-0.75" gas port for a mid-length is "tighter" across the board. Shouldn't there be a difference in gas port size between a mid-length and a carbine system?
Not being argumentative at all, really trying to wrap my head around the theoretical aspect of it. Obviously the ultimate test will be sending some rounds downrange, but trying to see if this brain-exercise matches up to what I will find when actually shooting it (maybe next weekend).
Thanks for adding your input!
Look at the Colt data, carbines are .062
Look at the Colt data, carbines are .062
Yeah, for carbine-length gas systems. The Hodge is a mid-length.
vicious_cb
05-04-19, 23:01
You really dont need a LMT eBCG in this kind of set up. The barrel was gassed to run on a mil-spec BCG and H2 buffer with 5.56 pressure ammo suppressed and unsuppressed.
I'm not sure how gas port size and location was originally determined. Was it based on engineered models and trial & error? With the exception of the mid-length system Colt seems to have figured/worked out some of the best data and specs. Today with higher quality ammo and the suppressor trend some manufacturers are reducing gas ports. For example Daniel Defense reduced the gas port on the MK18 to .069 from a .083. Mind you that .083 was a request by SOCOM which is widely known now to be over gassed but .069 is what Colt determined was best on their 11.5 carbines back in the 1970's. Sionics RGP 11.5 has a .063 gas port and though its advertised as for suppressor use only it cycles full power ammo unsuppressed all day long. So How are optimum gas port sizes determined today? I'm not sure if anyone knows as in yeah this is, we've tried everything already. Computer engineered models might test the many variations possible but until those theories are validated with live fire under varying conditions I don't think we know for sure.
You really dont need a LMT eBCG in this kind of set up. The barrel was gassed to run on a mil-spec BCG and H2 buffer with 5.56 pressure ammo suppressed and unsuppressed.
My intent is to run 20 rounds each of Mk318 and Mk262. I also have 20 rounds of M855A1 I found at a gun show a year or so ago that I'll use. I'll start with the M855A1, as spec'd with an H2 buffer. Then I'll move to the other two types of ammo. If I have troubles with cycling or lock-back (which I would only anticipate with the Mk318 and Mk262) then I will try an H buffer. If still having issues I will drop to a carbine buffer. If problems persist I guess the LMT EBCG goes back into storage! I have a lot of Mk318 and Mk262 so that is why I will test them subsequent to the M855A1, which I only have 20rds of.
Obviously this wouldn't be a test of the rifle's overall reliability given the uber-low round counts, but should give me an idea if the LMT EBCG can be used with this setup, even if I have to change buffers to make it so.
Torquetard
05-06-19, 04:03
I have an alleged .076 16" midlength and it sends brass into orbit no matter what
Have you shot the rifle at all? All this hypothetical discussion is great, but ultimately pointless.
I know eliminating the LMT EBCG would un-complicate it, but it's NIW and I want to use the damn thing (not to mention pricey also)! I also like them so would like to find a way to make it work in this setup if possible.
This is a very poor reason to use it in this setup. The EBCG was designed for a specific purpose that's well outside of what you're trying to use it for. I mean you can make a square peg fit into a round hole... if you have the right tools. Probably easier to use the right peg. PM me a price on the carrier if you're that tired of looking at it.
Have you shot the rifle at all? All this hypothetical discussion is great, but ultimately pointless.
No, as stated previously I have not. I will soon though, and will definitely post my results. The main gist of my question was whether going in reverse with buffer weights for less gassy barrels works like adding buffer weight for over-gassed ones, i.e. is the theory reversible?
This is a very poor reason to use it in this setup. The EBCG was designed for a specific purpose that's well outside of what you're trying to use it for. I mean you can make a square peg fit into a round hole... if you have the right tools. Probably easier to use the right peg. PM me a price on the carrier if you're that tired of looking at it.
I have 6 BCG's in storage. All but 2 are "standard" setups except for the coating/finish of a couple (a Colt standard, a Colt with a chromed Colt bolt in it, a Cryptic Coatings Mystic Black one, and a Sionics NP3 one). The other 2 are LMT EBCG's. If this experiment peters out then so be it. If I can get the Hodge barrel to run with an LMT EBCG and do so by playing with buffer weight then that's awesome. This is a new Colt 6920 OEM with the barrel replaced by the Hodge one. It has a Geissele SD-C trigger in it also. It'll be a keeper. I just want to see what I can make work.
Why is there any speculation it would not run with the enhanced LMT BCG?
No, as stated previously I have not. I will soon though, and will definitely post my results. The main gist of my question was whether going in reverse with buffer weights for less gassy barrels works like adding buffer weight for over-gassed ones, i.e. is the theory reversible?
The answer to the question is very much a “yes”. Gamers (not being derogatory) do this all of the time, to the point of also reducing carrier mass. These guns run on the ragged edge of reliability, however.
The reason I say it is useless to discuss an unfired rifle, outside of specing one out before building, is there are many variables than gas port and buffer weight that affect function in a duty-grade rifle. Without first shooting the rifle, it is hard to judge what the optimal set-up will be outside of a factory rifle. I would grab Federal XM855, H buffer, Sprinco white spring, and regular Colt carrier and go from there. It’s a boring, but thoroughly vetted, combination.
No, as stated previously I have not. I will soon though, and will definitely post my results. The main gist of my question was whether going in reverse with buffer weights for less gassy barrels works like adding buffer weight for over-gassed ones, i.e. is the theory reversible?The answer to your question is yes. Same principal as using a lighter buffer as underpowered .223 in a gun ported for mil spec 5.56. Will it work in your particular set up? I dunno. Maybe, maybe not. Sounds like you're just tinkering for the hell of it.
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Actually it is, especially if your gas is compromised in any way.
A 0.074 gas port is not on the small side. for a 14.5
SOCOM did not request a .083 and I have no idea where you got that. The MILSPEC for a MK18 is .071 or .070 depending on who you ask. DD MK18's were purposely overgassed for the commercial and LE markets to accommodate a wide variety of non-MILSPEC ammo which is what many companies have done in the past.
There is no standard for a midlength gas system, regardless or whether it is 14.5" or 16". The sole exception may be for the Geissele URG-I which uses a DD barrel and whatever gas port they established.
I'm not sure how gas port size and location was originally determined. Was it based on engineered models and trial & error? With the exception of the mid-length system Colt seems to have figured/worked out some of the best data and specs. Today with higher quality ammo and the suppressor trend some manufacturers are reducing gas ports. For example Daniel Defense reduced the gas port on the MK18 to .069 from a .083. Mind you that .083 was a request by SOCOM which is widely known now to be over gassed but .069 is what Colt determined was best on their 11.5 carbines back in the 1970's. Sionics RGP 11.5 has a .063 gas port and though its advertised as for suppressor use only it cycles full power ammo unsuppressed all day long. So How are optimum gas port sizes determined today? I'm not sure if anyone knows as in yeah this is, we've tried everything already. Computer engineered models might test the many variations possible but until those theories are validated with live fire under varying conditions I don't think we know for sure.
SOCOM did not request a .083 and I have no idea where you got that.
I got that directly from a Daniel Defense customer service representative.
The answer to your question is yes. Same principal as using a lighter buffer as underpowered .223 in a gun ported for mil spec 5.56. Will it work in your particular set up? I dunno. Maybe, maybe not. Sounds like you're just tinkering for the hell of it.
Pretty much this, because I have the parts on hand and it is interesting to tinker sometimes.
Why is there any speculation it would not run with the enhanced LMT BCG?
Because the EBCG was primarily made to "tame" (if you will) the 14.5" carbine length gas system of the M4. It does so by delaying the unlocking of the bolt, thereby allowing pressures to drop before doing so. The smoother recoil impulse of a mid-length gas system, coupled with the ever-so-tighter gas port of the Hodge barrel could tame things a little too much, causing short-strokes or failure to lock back on an empty mag.
Although not mentioned, the "odd man out" in this (and any fighting rifle's equation) is performance in extremely cold weather. A weapon that runs hunky-dory in a normal temperature range may not do so in extreme cold. There was a thread on it a while back on here. This is another whole issue but alas it is May in Tennessee so arctic-like conditions testing will have to wait!
I got that directly from a Daniel Defense customer service representative.
The DD representative was incorrect.
Actually it is, especially if your gas is compromised in any way.
Very true! .074 is lean as hell for a 14.5 middy.. I'd get it reamed to .076. To Gunz's point.... even at .076" 14.5 middy, I've had issues when gas was leaking at the key/tube junction. And I run an H buffer to lighten up the weight from an H2.
No, as stated previously I have not. I will soon though, and will definitely post my results. The main gist of my question was whether going in reverse with buffer weights for less gassy barrels works like adding buffer weight for over-gassed ones, i.e. is the theory reversible?
I did some testing with an SLR adjustable gas block. I tuned the gas block so it would eject, but not lock back with Federal 55 gr 5.56 ammo, H buffer and Colt carbine spring. Changing to a lighter CAR buffer made no difference.
I then opened the gas block one click so the AR would lock back on an H buffer. The AR locked back on a CAR, H & H2 buffer.
I then tuned the gas with a H buffer and LMT E-carrier to the minimum required to achieve lock back. Then, using the same gas setting, I tested a standard full auto carrier. It would eject, but not lock back. To achieve lock back with the standard AR carrier, I had to open the gas block one click compared to the setting for the E-carrier.
Well he is wrong, sorry.
I got that directly from a Daniel Defense customer service representative.
Which barrel?
I did some testing with an SLR adjustable gas block. I tuned the gas block so it would eject, but not lock back with Federal 55 gr 5.56 ammo, H buffer and Colt carbine spring. Changing to a lighter CAR buffer made no difference.
1 data point for you.
14.5" mid-length, BA Hanson, gas port .076", shooting XM193 to Mk.262
Running standard carbine spring and 1 tungsten/2 steel weights in the buffer.
Smooooth, but reliable. "Flat" shooting if you know what I mean, in the recovery.
I try to take care not to knee-jerk with tuning to more buffer weight because balancing that with spring weight is also a consideration; they interact. I want that thing to also be able to return and no-BS lockup again. I don't shoot for pretty piles of 4:00 brass. It reliably functions with 2:30-3:30 ejection & lockback from +5°F (so far) to normal summer temps.
1 data point for you.
14.5" mid-length, BA Hanson, gas port .076", shooting XM193 to Mk.262
Running standard carbine spring and 1 tungsten/2 steel weights in the buffer.
Smooooth, but reliable. "Flat" shooting if you know what I mean, in the recovery.
I try to take care not to knee-jerk with tuning to more buffer weight because balancing that with spring weight is also a consideration; they interact. I want that thing to also be able to return and no-BS lockup again. I don't shoot for pretty piles of 4:00 brass. It reliably functions with 2:30-3:30 ejection & lockback from +5°F (so far) to normal summer temps.
What H-level does that equate to?
The cold temp info is also relevant. Basically if all runs well at normal temps then a "cushion" should be allowed for extremes, namely cold or fouling. Kind of like the FN FAL gas setting: find the setting where it feeds and ejects then back off (or "open" more) two clicks for adverse conditions. In the case of the AR it might involve dropping the buffer by one, i.e. from an H to a carbine buffer.
What H-level does that equate to?
The cold temp info is also relevant. Basically if all runs well at normal temps then a "cushion" should be allowed for extremes, namely cold or fouling. Kind of like the FN FAL gas setting: find the setting where it feeds and ejects then back off (or "open" more) two clicks for adverse conditions. In the case of the AR it might involve dropping the buffer by one, i.e. from an H to a carbine buffer.Not sure of the formulaic method people use for H numbers. I "call" it an H1 - and I could be mistaken, open to enlightenment. An H for me is just a regular carbine buffer, 3 steel weights. Then get a pack of tungsten weights & experiment to roll your own. (Midwest Tungsten Svcs sells 'em in 3 packs, that's where I got mine.) But that setup works really well on both my mid-lengths. By contrast I also have a PSA carbine gas gun that needs an H2 with a Sprinco Blue Spring.
I'm with you on allowing that cushion for performance when things go south, or of long duration off the square range. Cold ammo=less pressure, or long fight=filthy gun; one can take their pick. Like I said I don't tune the gun per se to toss brass in some magic direction. But running with less than optimum conditions present is important, to me anyway. I was musing awhile back about how the level of knowledge available to someone who runs one of these things nowadays is light years ahead of what passed for working knowledge when I had one 50 years ago, lol. 'Course reasonably clean & well-lubed wasn't always happening either with some people.
:L
The buffer weight nomenclature is:
CAR - 0 steel, 3 steel
H - 1 tungsten, 2 steel
H2 - 2 tungsten, 1 steel
H3 - 3 tungsten, 0 steel
The buffer weight nomenclature is:
CAR - 0 steel, 3 steel
H - 1 tungsten, 2 steel
H2 - 2 tungsten, 1 steel
H3 - 3 tungsten, 0 steel
You da man! Thanks!
There is a distinct difference between a carbine buffer and an H buffer. Probably 90% of all the standard AR's on the market will function reliably with at least an H buffer.
Not sure of the formulaic method people use for H numbers. I "call" it an H1 - and I could be mistaken, open to enlightenment. An H for me is just a regular carbine buffer, 3 steel weights. Then get a pack of tungsten weights & experiment to roll your own. (Midwest Tungsten Svcs sells 'em in 3 packs, that's where I got mine.) But that setup works really well on both my mid-lengths. By contrast I also have a PSA carbine gas gun that needs an H2 with a Sprinco Blue Spring.
I'm with you on allowing that cushion for performance when things go south, or of long duration off the square range. Cold ammo=less pressure, or long fight=filthy gun; one can take their pick. Like I said I don't tune the gun per se to toss brass in some magic direction. But running with less than optimum conditions present is important, to me anyway. I was musing awhile back about how the level of knowledge available to someone who runs one of these things nowadays is light years ahead of what passed for working knowledge when I had one 50 years ago, lol. 'Course reasonably clean & well-lubed wasn't always happening either with some people.
:L
The buffer weight nomenclature is:
CAR - 0 steel, 3 steel
H - 1 tungsten, 2 steel
H2 - 2 tungsten, 1 steel
H3 - 3 tungsten, 0 steel
Thanks for that, really. Now I have the correct naming convention. :)
I was musing awhile back about how the level of knowledge available to someone who runs one of these things nowadays is light years ahead of what passed for working knowledge when I had one 50 years ago, lol.
Oh that's absolutely correct. Between the internet and technology the understanding of an AR is eons beyond what you reference. Hell, it's eons beyond what I experienced carrying one for Uncle Sam in the mid-80's (which was an M16A1, probably not much different than you had). Of course with a full-size rifle not much has changed tweaking-wise, but carbines? Katy-bar the door! Buffer weights, port sizes, A5 buffers, enhanced power springs, a shit-ton of different ammo/bullet weights, enhanced BCG's, etc. Oh yeah, the plethora of tweaking options blows away the past.
For instance, port size over-gassed or a little on the tight side? Up or down with buffer weights, regular or extra-power spring, maybe an enhanced BCG. Then there's the A5 thrown into the mix as a possibility. This can be kind of fun stuff to play around with to find the "sweet spot".
Of course the downside is the complication of things.....50 or 35 years ago it was 55gr with 20" barrel and rifle buffer. That (generally speaking) was it, period. Having said that, I like a challenge! ;)
Which barrel?
It's an 11.5" SS carbine length barrel I got from PSA. I don't recall the original port size.
When I say the buffer weight made no difference, I mean it made no difference operationally. Both buffers functioned fully on the same gas setting. Both buffers would eject but not lock back when the gas was closed one click. Same when the H2 buffer was tried. But buffer weight made a significant difference in how the recoil felt. Recoil was uncomfortably sharp with the CAR buffer. It was softest with the H2 buffer.
Good info.
The different gas system configurations can act a little differently.
It's an 11.5" SS carbine length barrel I got from PSA. I don't recall the original port size.
When I say the buffer weight made no difference, I mean it made no difference operationally. Both buffers functioned fully on the same gas setting. Both buffers would eject but not lock back when the gas was closed one click. Same when the H2 buffer was tried. But buffer weight made a significant difference in how the recoil felt. Recoil was uncomfortably sharp with the CAR buffer. It was softest with the H2 buffer.
Good info.
The different gas system configurations can act a little differently.
It's an 11.5" SS carbine length barrel I got from PSA. I don't recall the original port size.
When I say the buffer weight made no difference, I mean it made no difference operationally. Both buffers functioned fully on the same gas setting. Both buffers would eject but not lock back when the gas was closed one click. Same when the H2 buffer was tried. But buffer weight made a significant difference in how the recoil felt. Recoil was uncomfortably sharp with the CAR buffer. It was softest with the H2 buffer.
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