Home Forums Hunting & Shooting AR and Tactical Rifles What buffer/spring for my AR15?

Purchased most the parts so far for my AR15 build, but apparently neglected to verify the buffer tube/stock combo I purchased came with a buffer and spring. Using rifle length gas on an 18" barrel, A1 stock (and hence a rifle buffer tube), BCG is a nickel-boron Toolcraft, and it's chambered for 5.56. Figured I'd take the opportunity to see if there's a specific buffer and/or spring people have found works best on builds similar to mine, any recommendations?

If you have a rifle buffer tube, you will need a rifle buffer and spring.

It’s only in the carbine buffer tubes or VLTOR tube that you have various buffers and springs.

I REALLY like Slash's Heavy Buffer and Wolff springs in A1/2's,or anything rifle buffer tube'd. Hint................

Standard rifle buffer is in my A1 receivers. You can use a carbine buffer in a rifle tube with a spacer, but you'll want to approximate rifle buffer mass. I've used my MGI buffer that way. Don't forget to use the spacer.

I’d just run a regular ol rifle buffer and spring to keep it simple. I’d also put a little white lithium grease on the spring. There’s also the armaspec captured spring systems that work well. Those require a spacer, but work well from what I’ve seen. One of my buddies kept complaining about the sproing sound coming from his A2, so I gave him one of these captured spring systems and he is very happy with it.

Green Springco for the spring and start with the standard 5 oz rifle buffer.

18 inch rifle gas barrels are easy to get undergassed with the short dwell time.

Any idea of the gas port size?

Will you be suppressing it?

Port size is whatever is standard on the Faxon Gunner (0.093” iirc), and I won’t be suppressing it.

I know I'm the black sheep here, but even 20" 5.56 barrels should have the gas port backed up about an inch. Originally designed, it's not in the right location to have the system in the center of the operating window.

The current trend to keep moving the gas port forward, is just ridiculous. Sure it works, but you're getting close to the edge of the operating window of the system.

Tony

I think the operating window is (has been?) reevaluated by the industry. Even 14.5" mid-length barrels have proven themselves to be very reliable.

As the Mil spec for 20 inch rifle gas port size is .093" and we can go to .125" there is a lot of space left if one feels the need for more gas.

Crane speced the MK12 18 inch rifle gas port at .105" and without the issued suppressor thats to small in the cold and/or at high altitude.

A .115" port in the 18 inch rifle gas barrel will run quite well at sub zero and high altitude with 5.56mm mil spec ammo unsuppressed.

A fact of gassing the AR is that the further you can move the port down the barrel the lower the chamber pressure will be when the system exracts the case. Lower pressure during extraction always means less wear and tear on bolt lugs and less chance of failure during the case extraction.

With the continued and expanding use of suppressors one should simply design the gas system for suppressed use.

Mid lenght (9 inch) gas works really well on 11.5-12.5 barrels as the added dwell time from the suppressor provides plenty of gas and the longer lenght reduces the extraction forces from a carbine gas system (7 inch).

Rifle gas on the 18 inch is great for suppressed/unsuppressed use and the further we move the port down the barrel the more forgiving the system becomes to unsuppressed/suppressed shooting.

The future is simply gassing the AR to run suppressed all the time.

I realize much of what I posted is understood by them that know but it adds some context for those that are exploring the AR.

In all my.infinite wisdom, I normally shop around for an inexpensive buffer tube and spring
Normally, I end up with a MOG stock, tube and spring.
Other than installing an AR15 tube and spring in an AR10 😜, I've not had any problems.
I try not to overthink things too much! 🙂

Actually John, you can go bigger than that despite the gas tube being .125". A 16" 50 Action Express upper with a carbine gas system won't run at .125", but will run with a .144" barrel and gas block port.

I think everyone just assumes the flow limit through the barrel's gas port is .125" due to the gas tube, but no one has actually tested it.

In my testing with the 50AE back in the 90's, the flow limit is .157", not .125". Opening the port from .125 to .157 gives you significant gains, but past .157" doesn't get you anywhere.....at least with a 50AE.

But I don't know, it just doesn't seem like a really good idea to have your small caliber bullet running over a monster pot hole on one side of the barrel. I really need to test that....it might be better to drill through and have equal opposing pot holes. Accuracy speaking.

Tony

Tony,

The context of the OP was .223/5.56mm.

I don't have your level of experience in those big bore ARs because I don't have any experience with over 30 cal ARs.

So view my post in the context of the OPs .223/5.56mm 18inch barrel.

I used the .125 gas block port as a max simply because I never need anything bigger.

Thanks for sharing your knowledge of the big bore ARs.

I just purchased two of the the JP Enterprises silent captured springs. I don’t have the barrel length mentioned, I have the 24" Varminter barrels. It works good and plan on more in the future.

Higher port pressure and shorter dwell translates as more violent. But evidently not enough so, witness the dotgov shift to M4 carbines. There can be sufficient extractor lift to result in dropped extraction with the carbine gas system. That was addressed with extractor insert or x-power spring.

Mack Gwynn told me extractor lift occurs even with 20" rifle gas system uppers, but doesn't rise to a level of significance. Don't know whether the carbine gas system eventuates as greater parts wear/breakage?

Violent extraction (short dwell, high pressure) can run with over-cycling. But my understanding is they're not necessarily the same thing - thinking 9mm with non-ramped bolts here. But as round count increased on one of my 11.5s noticed ROF increase. Not going to tolerate trigger slap and risk egged FCG holes with reg receivers.

Still use that 11.5", but only with what's left of my Wolf black box poly. It's seriously underpowered and, as said, using rifle stock and buffer......the original rate-reducing system.

The 5.56 carbine system taps gas at about 26K PSI, mid length about 17K PSI and rifle about 13.5K PSI. Actually shorter dwell time (time the bullet passes the gas port until it leaves the barrel) is easier on the bolt and various parts. That’s why a carbine gassed 16” barrel is not as smooth cycling as a carbine gassed 14.5” barrel. Same with mid and rifle gassed barrels, they just run smoother.

9mm or at least most 9mm AR’s are blow back, not gassed. So it’s a totally different animal.

Heavier springs and buffers delay the unlocking of the bolt, preventing the extractor from pulling rims. Another part of the buffers job was to prevent bolt bounce on full auto and according to a Colt engineer, varied with the weight of the gun.



And gas port erosion doesn’t wear straight through the hole, it runs out towards the muzzle.

Stole this pic too long ago to remember who to give credit to.

Thanks, TWR. Is the gas port diameter spec for 16" smaller than that for the 14.5"?

Have a Teslong pic of my 11.5" blaster's port that correlates with your pics. Haven't figured a way to post pics from the computer on this site. File size always too big.

At one time Colt used the same port size but I have heard the new CZ Colt has deviated to a bigger port size on all their guns. Buddy of mine says their issued 11.5” guns are way over gassed. He wound up putting a BRT reduced gas tube in his.

Found a file I'd saved in '14. Colt gas port specs (guessing around that time):

* 10.5" - .093
* 11.5" - .081
* 14.5" - .063
* 16" - .063

So guess that answers my own question, and explains why a 16" would have relatively more gas at port vs 14.5"