How to tell if a AR is over or under gassed?

84ta406

Dealer
NES Member
Rating - 100%
32   0   0
Joined
Nov 8, 2014
Messages
1,763
Likes
838
Location
Leicester MA
Have a new AR build Ive been playing with lately and while there has only been one hiccup, I am wondering if the gas system can be tuned more to improve on anything. This is my first AR, let alone one I built. So how would I know if it is over or under gassed? My brass is ejecting normal, slightly back at like 4-5oclock position. My one hiccup the bolt jammed feeding the next round and got stuck about 1/8" down from the neck. Dropped the mag, cleared the round and kept going, not another hiccup. I only have 200 rds through it, and its been great, just looking for ways to get the maximum potential.
 
Rating - 100%
3   0   0
Joined
Apr 21, 2016
Messages
1,013
Likes
100
Location
Chicopee
Try different Ammos. I know my AR will act differently shooting different ammo. If I'm shooting steel cased Tula or wolf it ejects at 4-5 o'clock. But the second I switch to federal 5.56 it ejects at 2 o'clock. Iv found most if not all of my issues were magazine related.

What at buffer spring are you running. Carbine or rifle length buffer and gas tube.
 

84ta406

Dealer
NES Member
Rating - 100%
32   0   0
Joined
Nov 8, 2014
Messages
1,763
Likes
838
Location
Leicester MA
Try different Ammos. I know my AR will act differently shooting different ammo. If I'm shooting steel cased Tula or wolf it ejects at 4-5 o'clock. But the second I switch to federal 5.56 it ejects at 2 o'clock. Iv found most if not all of my issues were magazine related.

What at buffer spring are you running. Carbine or rifle length buffer and gas tube.
I used Winchester WB 5.56, Federal AR223, Aguila 5.52 62gr and Aguila .223, all were great.

The buffer and spring are carbine length and weight but I am also using a rifle length gas system and Syrac Adj. gas block.
 

northny

NES Member
Rating - 100%
8   0   0
Joined
Aug 12, 2010
Messages
1,030
Likes
627
Location
Between Cabelas and Harvard Sportsmen’s Club
I have syrac adjustable gas block on a new upper build. Had a few failures to feed that were related to both new bcg needing a thorough scrubbing and rifle needing to be cycled a few hundred times. All failures were in first thirty rounds before scrubbing bcg. Never changed setting on gas block after initial setup per Syrac instructions and it has been flawless since. I suggest you are fine.
 

greencobra

NES Member
Rating - 100%
24   0   0
Joined
Jul 2, 2011
Messages
15,930
Likes
7,468
without seeing it i'd say maybe a mag problem, or ammo, or feed ramp. it pulls the case out, ejects, and picks up a new round. it just won't feed it sometimes.

i just built a 7.62x39 on an ar platform that i'm guessing is overgassed. it throws empties 10 feet away, maybe more. and they don't touch the deflector. i'm going to try an adjustable gas block but in the meantime it could make the shooter next to me extremely cranky.
 

84ta406

Dealer
NES Member
Rating - 100%
32   0   0
Joined
Nov 8, 2014
Messages
1,763
Likes
838
Location
Leicester MA
I was leaning towards mag problem as well. I was using a Colt 20rd mag when it happened. Didnt happen with my pmags at all. It was only the one problem though.
 

greencobra

NES Member
Rating - 100%
24   0   0
Joined
Jul 2, 2011
Messages
15,930
Likes
7,468
I was leaning towards mag problem as well. I was using a Colt 20rd mag when it happened. Didnt happen with my pmags at all. It was only the one problem though.
did you try other 20 rounders? no sense going anywhere with this if it only happened with one magazine. if it works with pmags and not an odd 20 rounder.........
 

84ta406

Dealer
NES Member
Rating - 100%
32   0   0
Joined
Nov 8, 2014
Messages
1,763
Likes
838
Location
Leicester MA
I was using another 20rd Colt mag as well. Im not worried about the malfunction that much really. I am just making sure everything is working properly. There is a TINY bit of black soot on the barrel where it meets the gas block. Not sure if that matters.
 
Rating - 0%
0   0   0
Joined
Oct 3, 2013
Messages
42
Likes
10
without seeing it i'd say maybe a mag problem, or ammo, or feed ramp. it pulls the case out, ejects, and picks up a new round. it just won't feed it sometimes. i just built a 7.62x39 on an ar platform that i'm guessing is overgassed. it throws empties 10 feet away, maybe more. and they don't touch the deflector. i'm going to try an adjustable gas block but in the meantime it could make the shooter next to me extremely cranky.
While I doesn't solve the problem of over-gassing ... how about a brass catcher? Not to steal the thread, but did you build or buy your 762x39 upper?
 
Rating - 100%
27   0   0
Joined
Jul 13, 2005
Messages
7,791
Likes
1,066
Location
Eastern Mass.
take the carrier out and remove the bolt. put the carrier back in the upper and slide it back and forth by hand. does it slide smoothly or get caught up on something. if the carrier is not aligned with the gas rod then bend the gas rod to fit better.

did you put grease on the recoil buffer spring? hopefully not. also you can play around with lighter buffers but it seems like it's working okay.

also, CLP on the carrier group never hurt.
 

92G

NES Member
Rating - 99%
98   1   0
Joined
Mar 19, 2014
Messages
7,529
Likes
3,581
Location
Pangea
OP whats your barrel length?

Just keep shooting it. Most likely malfuntion a product of new upper needing to be broken in by BCG.

My guess is if anything you are undergassed. Cant see any reason your setup would be overgassed. If youre sufficiently undergassed the issue with show itself.

can also try a few tricks like not shouldering the rifle (limp wristing ewuivalent for rifle) and test if functioning + if last round in mag fired leads to bolt hold open or not. Typically if undergassed the issue will be failire of extraction or ejection over a feeding issue.
 

84ta406

Dealer
NES Member
Rating - 100%
32   0   0
Joined
Nov 8, 2014
Messages
1,763
Likes
838
Location
Leicester MA
Barrel is 20" with a Lantac brake on it.

I wasnt so much worried about the malfunction. Just figured it was worth mentioning. I was just curious what signs there are to over and under gassing. Also after looking at some of the brass it looks like theres some gouging on some of the bases where it says what caliber etc. Ill take a couple pics when I get home.

Im just curious if tuning the gas can make it shoot any different/ better.
 
Rating - 100%
66   0   0
Joined
Dec 26, 2008
Messages
27,494
Likes
4,576
start with mags, isolate mags as you have malfunctions. Then see if they repeat with use of that mag.
You have adjustable gas block did you set it up to each ammo to see how it performs?
the advantage of the adjustable gas black is that you can actually induce symptoms of high or low gas pressure.

Crank the adjustment down until the bolt doesn't move then open it up until it just functions then go from there. using mixed ammo you may need to tweak it until it will cycle anything you get in the 55-62 grain weight range with out being over gassed


there is a couple more also
 
Last edited by a moderator:
Top Bottom