Home Forums Hunting & Shooting AR and Tactical Rifles Wisdom sought: balancing buffer weight and gas flow

So, I've been fooling with large frame ARs for a little while now. Definitely a different kind of adventure. Some stuff just doesn't combine well with other stuff.

I have two guns I use for hog hunting, both chambered in .260 rem. The first came around without much heartburn. Ejection may be a bit too vigorous, but it wasn't really over the top last time I fired the gun without a brass catcher. Interestingly enough, I found that the gas tube is about 1/4 inch shorter than it should be---something that escaped notice for the last eight months or so.

The other gun is another story. I'm sure it's still over-gassed. Ejection seems to be about two o'clock, but sometimes a little more vigorous than that it seems.

I have the buffers for each gun stuffed with as many tungsten weights as they'll hold (five each, IIRC) but things still are not right...A2 style stocks & buffer tubes, to be clear.

So, last week I ordered a pair of adjustable gas blocks. I bought the JP clamp-on style and have installed them. I have yet to take the guns out and see about tuning things up, thinking sometime this week I can get to it.

So, since I've done nothing with them yet I'd like to know how to approach all this to resolve my problems. I could just go and adjust the gas so that ejection is a bit more gentle, but I think that may not be the optimal solution. Do I need to evaluate things further? Is there more to consider? Could my buffers be too heavy, and how would I know? I think I've got what I need to get things straightened out but I'd like to be sure I'm not overlooking something important and I'd appreciate any real expertise and good advice

TIA.

I always hear about these issues. Glad I don't have to deal with it. I just run regular ol buffers and springs. No AGB. AR10's and AR15's, don't matter. Sometimes it's better to just keep it simple. Good luck, hope you figure it out.

Put your buffers back to their standard configuration, set gas block one setting above closed and shoot. Keep adjusting gas block until it runs reliably.

Okay, that's simple enough to do but I want to know why. Some folks just want to know which buttons to push, but I'm not wired that way.

I'd have to research to find out what the standard buffer weight is because I don't recall. These are LR-308s, A2 stocks w/rifle buffers, BTW.

Rifle buffers weigh 5.3 oz. They retard the bolt movement until chamber pressure drops enough that the case is not stuck to the chamber so it can extract easily. The movement of the weights inside reduce bolt bounce on full auto. The rifle spring is longer and softer than a carbine spring.

The standard gas port size and placement releases a quantifiable amount of gas down the tube to move the BCG back. Balanced between the cartridge pressure, gas port size and position (rifle, carbine, mid or intermediate), buffer weight and spring rate, the gun runs fine.

Get it out of balance like too big of a gas port, +P cartridge, weak or over powered spring, light or heavy buffer and it all goes to hell. It's a balance even affected by extreme cold or hot temps. That's why no one can say for sure that you need X buffer or X size port until they know all the particulars. The adjustable gas block allows you to control this if the rest is out of whack.

For the most part, carbine sized AR-10's in say 308, needed a heavier buffer that wasn't available until a guy on ar15.com who went by Slash, started making extra heavy buffers for them. For the most part rifle AR-10's were worked out pretty well but still benefited from a heavy buffer.

So start with a standard rifle buffer and spring, set the gas block on it's first setting and test fire. Adjust as you need to and if you need to tweak anything you can but do it one thing at a time and start the process over. Try it in the winter time and the heat of summer.

One thing to watch for is pulled rims. If the buffer is too light and you give it enough gas, it will extract the case before pressure drops and the extractor will bend the rim. Worst case you can have case separation and being over gassed is hard on everything. Being under gassed or too heavy a buffer won't always let the case eject reliably.

And the chart above is just a reference, you can cut the ejector spring and make brass land wherever you want it to.

AGB's are your friend.

I like to keep buffers & springs on the lighter/moderate side & control gas as needed.

When tuning, close of the gas to the point of which the bolt will not lock back with an empty mag then open a quarter turn at a time until you are satisfied with reliability. And see h ow your brass looks, as far a the rim for any kind of stress / damage goes.

Ammo does have an effect especially from commercial to NATO.

Good luck.

MM

Thanks, guys. I'll get the rifles out to the range this week iand see what I can accomplish.

I may report on a number of things since I'm trying out some new E&L Mfg. brass catchers. I got tired of waiting for the folks at Brass Goat to get their large-frame AR brass catcher to market (I suspect they're finding out there are too many mag well variations to make the design work, but hopefully they'll pull it off...I LOVE the ones they make for AR15s!).

Man I finally got that AR10 I had back to the guy that first wanted me to get it straitened out, then tried to sell it to me. Hated that boat anchor. It was a truly accurate rifle but function was nothing like any of my AR15's experiences. I finally got it where it was both reliable and accurate by running I4895 at moderate pressures duplicating military specs. Regular factory ammo pushed more gas than the design wanted to function with. The carbine stock it came with WTH? He balked when I wanted to put an A2 stock on it to make it easier to shoot. I smiled when I pulled that thing out of the safe and handed it to him. He put a lot of money in it.

Update: I had little to no trouble getting my new JP Ent. adjustable gas blocks dialed in. I got nice and consistent 3:00 ejection with consistent lock-back on an empty magazine. My hog guns are dialed in, except for a few things I had to do to make my new E&L Mfg. brass catcher work on the gun with the thermal scope mounted. Maybe I'll write that up later. I discovered I had an issue while trying to sight that gun in but I think I've got that ironed out now. Gotta get back out there and verify my sight-in on that rifle.

^^^^This!^^^^

Nor I.
Life is difficult enough as it is without AGB's etc.
I haven't built tons of AR's, but enough to believe an AGB is more trouble than it's worth.
I blog on another site that concentrates on AR's.
Those crazy guys are unbelievable!
"I'm under gassed even with the AGB wide open,so I opened up the port on the barrel by .035". Now it's overgassed!"
They want to "Lok-Tite" the gas block to seal it around the gas port. 😖

"I'm shooting a 65 grain bullet at 2900fps out of my 5.56, do I need to add more weight to my buffer if I change to a 45 grain bullet?" and vice versa!
"My .300ACC is ejecting brass at 245 instead of 3 o'clock, should I open the AGB or drill out the barrel gas port 80 thousandths?" Whut......?

I purchase parts online. I try to buy common, everyday "pieces/parts" and stay away from the extremely expensive and dirt cheap.
Building an AR is easy.....as long as you don't over think it!


I've had 2 DIY builds that failed their first test fire.
Both due to errors I made during assembly.
Corrected the problem! Problem solved!

No, they are really not more trouble than they are worth; it really depends on what you are trying to accomplish with a given build..............like wanting to use a lightweight BCG / buffer to help minimize felt recoil & gun movement.

Of if you have a barrel that is truly over-gassed or near to being so (yes, they do exist) & you're not really interested in using a 5 lb buffer & a 100 lb spring to tame it.

But then again, even some simple things are difficult for some to deal with......................

And large frame AR's are surely not exactly like small frame guns either & since all the uppers & shell deflectors are not exactly of a common design, ejection angle is not always as dependable an indicator of BCG speed or gassing either.

But, YMMV

MM

I never use an adjustable gas block, I run heavier buffers to tune the rifle

YMMV

Well, yes, MMDV, & that's the point.

I simply don't like adding lots of reciprocating mass to the system much past an H1 buffer.

If you need more than that, something is not quite as it could be/ should be.

So for me, I prefer to use an AGB instead of adding more weight.

MM

"... help minimize felt recoil & gun movement. ..."

Already doing that!

Built a DIY AR on an Anderson upper/lower in 6.8mm.
No AGB and a plain Jane buffer and spring off the shelf.
Kills deer dead and is very comfortable on my shoulder implant! 👍

The Principle of Parsimony

"It is pointless to do with more what is done with less."

What's a Plain Jane buffer & spring?

C, H1, H2, H3, 6oz, 10 oz? Ditto for spring?

Please rock on in your world with walls, you're beyond myopic.

MM

For my World,I HATE adjustable gas. Hint.

For a blasse' build,where Lightweight isn't a focus and especially in large frames,I always want a Slash HEAVY Buffer. I prefer the dampened cyclic rate and mild mannerisms associated. Hint..............

Your dislike for AGB's are well known to those that actually pay attention to your various posts over time, as is your preference for ole' Slash's wares

And, I agree, that adding weight will make most stuff run.................but at some point, I prefer not to keep adding weight to an already heavy gun, & for "lightweight" builds, especially, where I want to keep weight down, AGB's are another tool. And the good ones work fine.

That's also a reason that I just pretty much refuse to fu^ck around with Carbine gassed guns for my own use; I'll take intermediate & rifle gas in 16" or 18" barrels everyday, all day.............& as a rule on the better barrels (read that as gassed right) of those configurations, there's usually not a need for an AGB unless using reduced velocity loadings (like for hoser stages in gaming) or a lighter weight BCG. And I check gas port size on barrels I get.

But you already know & comprehend all that, as compared to some of the ladies posting here........................

MM

The gals are always going to do their best,which is the only reason it's sooooooo reliably fhuqking funny. Hint.(grin)

I'm a NOTORIOUS Rifle Gas Slut and 18" is warm/fuzzy. Headed out now,to Test Drive a Brownie MPO 1-6x Donut upon same. From the hip,SFP obviously isn't my jam,but for a Winter Wonder Land Play Toy,I believe it can be pressed into service,as a Fur Fightin' Sight. Seldom during a Cast & Blast,do I have to subtend afar and Spittin' Distances are a frequent Theme. It should cover that modest spectrum nicely. Capped turret probably don't piss me off there,but it sure as fhuqk isn't a Swiffer 1-6x HD MQ FFP Lit Bitch. Hint.

I'm trying not to be jaded,with others wearing BTR Gen 2 FFP '12x Lit Bitches,which are simply fhuqking SENSATIONAL in their versatility. Hint.

First World "problems" all. Hint.

Fhuqking LAUGHING!..............