AR15 problem. Gas system?

[gerrycaruso]

I know very little about AR15s but I think this is a gas problem. The rifle started doing this a few days ago. It's a couple of years old and has been used very little. It feeds, fires and ejects the first round fine but usually the bolt won't move rearward far enough to pick up the next round. The gas key isn't loose, the rings seem fine and the gas block is all the way back. I don't know what else to look at.

 

[lukewarm_fuzz]

Clean it recently? It could be fouled or you could be using lower pressure ammo than you did previously. After that I might try a lighter buffer weight.

 

[FalArAk]

Maybe the buffer spring is bound up or try cleaning the BCG.

Then move to the more difficult things

 

[50wt]

I know very little about AR15s but I think this is a gas problem. The rifle started doing this a few days ago. It's a couple of years old and has been used very little. It feeds, fires and ejects the first round fine but usually the bolt won't move rearward far enough to pick up the next round. The gas key isn't loose, the rings seem fine and the gas block is all the way back. I don't know what else to look at.

Shouldnt there be a gap between the gas block and barrel ? pull the gas block and make sure there are no restrictions in the gas tube.

I'd pull everything out , wipe everything down , and lube it with a few drops of something light like wd40 or silicone spray.

 

[LakeTrout]

I know very little about AR15s but I think this is a gas problem. The rifle started doing this a few days ago. It's a couple of years old and has been used very little. It feeds, fires and ejects the first round fine but usually the bolt won't move rearward far enough to pick up the next round. The gas key isn't loose, the rings seem fine and the gas block is all the way back. I don't know what else to look at.

If the problem is the bolt won’t move rearward enough, you may not be getting enough gas to the gas key or your buffer and spring system may be too heavy.

All the way back isn’t the correct position for the gas block to be in, although it should still work in that position. It still could be misaligned.

 

[Bodhisattva]

What brand is the upper? What length is the barrel? What length is the gas system?

 

[PatMcD]

It's always worth a quick look inside the bore to see if the gas holes in the barrel and gas block are completely lined up.

 

[Asaltweapon]

It's always worth a quick look inside the bore to see if the gas holes in the barrel and gas block are completely lined up.

I worked on a friends rifle doing the same thing.
First thing I did was shoot some brake cleaner in the gas tube and nothing came out. His gas block had shifted on the barrel.

 

[F2386]

Load one round into your mag and fire. If it locks open on the last round then it's not your gas system. I'd go through the following motions -

1) Check magazines first - springs, feed lips and etc. Try different magazines to see if the issue persists.
3) Look for fouling, build up, lubrication
4) As a last resort I'd start replacing stuff like BCG, buffer spring and weight until stuff starting cycling

If your magazine doesn't lock open then it's likely a gas issue -

1) Check the ammo - some ammo is notoriously underpowered and inconsistent. Try different brands of ammo.
2) Get a borescope and check gas port alignment. You can get one on Amazon for $60.
3) Start replacing BCG, buffer system until it cycles

 

[1903Collector]

I know very little about AR15s but I think this is a gas problem. The rifle started doing this a few days ago. It's a couple of years old and has been used very little. It feeds, fires and ejects the first round fine but usually the bolt won't move rearward far enough to pick up the next round. The gas key isn't loose, the rings seem fine and the gas block is all the way back. I don't know what else to look at.

Did you fire it previously? and if so did it work ok? if it did, I would start with ammo and mags and go from there.

 

[gerrycaruso]

It worked fine a few days ago. It feeds fine from this magazine when I pull the charging handle. Different ammo (green tip) did the same thing.

 

[Tweed]

ARs like to run wet.

 

[gerrycaruso]

As I said, I know almost nothing about ARs but it seems to be a gas problem. If the bolt won't come back far enough to pick up the next round, it certainly won't come back far enough to lock open. I haven't looked but I'm guessing the gas block shifted and the hole in it and the hole in the barrel are no longer lined up. Thanks Asaltweapon.

 

[LakeTrout]

As I said, I know almost nothing about ARs but it seems to be a gas problem. If the bolt won't come back far enough to pick up the next round, it certainly won't come back far enough to lock open.

Most likely, you’re right. But it’s a pretty good test and standard troubleshooting for this type of issue.

What weight buffer do you have, and do you know if you have a standard power spring or something heavier?

 

[F2386]

As I said, I know almost nothing about ARs but it seems to be a gas problem. If the bolt won't come back far enough to pick up the next round, it certainly won't come back far enough to lock open. I haven't looked but I'm guessing the gas block shifted and the hole in it and the hole in the barrel are no longer lined up. Thanks Asaltweapon.

Everything you've described so far indicates a magazine spring issue. Mag springs can weaken or get bound up and fail to feed the next round, among other issues. Are you using old USGI mags or are you using something newer like a pmag? Pulling on the charging handle to chamber a round isn't indicative of a functioning magazine.

If you're certain the magazine isn't the issue then I'd check everything else before messing around with the gas block. By all means, get a borescope and rule out the GB. It's just the least likely of issues IMO. If your GB is a clamp on or has set screws then yeah it's possible it moved. But if it's pinned then I doubt that's the cause.

 

[Bodhisattva]

Before you go crazy. Try some different mags, some of the cheaper mags have weak springs or shitty followers. If you have another rifle, swap the uppers. It could be the lower out of spec. Had issues with the lone Anderson I own doing this. Tried several different uppers. Changed out the lower, no more issues. My bet though is gas block alignment.

 

[gerrycaruso]

Yes, it is an old G.I. magazine. I'll try a much newer P mag.

 

[DPR]

If your new to AR, learn how to inspect your bcg and identify areas not to spec and that could leak gas

 

[Dench]

I know very little about AR15s but I think this is a gas problem. The rifle started doing this a few days ago. It's a couple of years old and has been used very little. It feeds, fires and ejects the first round fine but usually the bolt won't move rearward far enough to pick up the next round. The gas key isn't loose, the rings seem fine and the gas block is all the way back. I don't know what else to look at.

Check the magazine.

I had a large pin preban colt mated to a normal upper via an offset screw. It 100% sucked ass as it would not have the proper distance of seperation from the lower and upper which led to the bolt carrier grinding on the magazine.

Wasnt till i finally sourced a factory new large pin upper that this nightmare was fixed.

 

[gerrycaruso]

This is a problem that just started a few days ago. Prior to that everything was working fine. It would be great if it's something as simple as a new magazine spring, which I have many of but I'm not hopeful.

 

[Bodhisattva]

Is it a USGI 30 or 20? I’ve seen more worn springs in the 20s than 30s

 

[40 Creedmoor fan]

Something that haven't been mentioned here: The gas port size may be too small. I seem to remember reading an article on Sons of Liberty gun works web site.
Apparently, low-cost manufacturers don't bother switching drill bits and crank out barrels wit the same gas port diameter. May be worthwhile to check

Here's a good reference: AR-15 Gas Port Sizes

 

[gerrycaruso]

Something has worn or changed because it used to work fine and it's a 30 round magazine.

 

[Bodhisattva]

Something has worn or changed because it used to work fine and it's a 30 round magazine.

Yea it’s prob the spring, and or follower. Still won’t hurt to check the gas tube at the least.

 

[paul73]

It worked fine a few days ago.

the most usual things there would be dirt/tolerances/friction. it is probably colder now than it was first time you tried it.
first thing - if you pull the charging handle, is it stiff/tight to get the bolt out? are the ribs of the bolt dirty?

try to clean it all very well, then pour a lot of oil on bolt, and try to shoot it more. if it is brand new and pretty much unbroken - then most likely it still rubs quite a bit and when it got colder - it got tighter and now does not move free anymore.

i do not think it is gas, as it is highly unlikely. it is only if gas block was never set right or was not tightened at all, which is possible, but very unlikely.

 

[Tartakovsky]

Sounds like short stroking. The buffer spring or buffer maybe too heavy/stiff. The upper should also be well lubed, even lube the spring. If it’s a factory upper, probably not the gas block/gas tube. You running full powered ammo? Or cheap wolf steel cased? It’s likely in need of lube, a carbine buffer spring and carbine buffer. If it’s a light recoiling rifle, you may want to try a springco white or even springco yellow spring.

 

[paul73]

The buffer spring or buffer maybe

it is not a thing that just mutates by itself with time. if it ran fine before - it is not it, i would think.

 

[Tartakovsky]

it is not a thing that just mutates by itself with time. if it ran fine before - it is not it, i would think.

If it’s dry, it probably needs to be lubed and also probably needs to be racked a bunch of times. Could also be the mag and could also be the ammo.

 

[paul73]

probably needs to be lubed

definitely.
pour good amount of oil on it, and shoot 3-4 mags, and bolt will mate into the guides. it needs to strip excess paint and finish off where it rubs. just needs to be broken in.
i just did it to my brand new cheap aero upper. but, got to say, it did not like my other spare extra cheap bolt, and i set it with an andersen bolt that i ordered later - it has better tolerances.
the cheap ass spare one was/is a bit too tight, dunno where i even got it, it was about $40 or so. visually look ok, but does not run great.

 

[LakeTrout]

the most usual things there would be dirt/tolerances/friction. it is probably colder now than it was first time you tried it.
first thing - if you pull the charging handle, is it stiff/tight to get the bolt out? are the ribs of the bolt dirty?

try to clean it all very well, then pour a lot of oil on bolt, and try to shoot it more. if it is brand new and pretty much unbroken - then most likely it still rubs quite a bit and when it got colder - it got tighter and now does not move free anymore.

i do not think it is gas, as it is highly unlikely. it is only if gas block was never set right or was not tightened at all, which is possible, but very unlikely

If the rifle is malfunctioning like this due to colder temps, then something is way out of spec. Even cheap AR15s are very reliable and would not need oil poured all over the bolt unless something is very wrong. This is a system that runs for a very long time without maintenance, except for under the harshest conditions.

Clearly, something is not right, and it’s not because it’s dirty or cold. Maybe pouring oil all over everything will get it to function temporarily, but there is a deeper problem here. Not enough gas making its way back to the BCG, worn mag springs, too heavy of a buffer system, etc.