AR-15

[c172skyhawk2]

I just finished building an AR and I cannot get it to cycle properly to pick up the next round. Most of the time the spent shell will be extracted but will not pick up the next round or lock open.

It has a 16 inch govt profile barrel ,carbine gas system and a YHM low profile gas block. I have taken the gun apart several times and nothing changes. I can blow through the gas tube and it seems free and air comes out the gas block hole. I can plug the hole in the gas block with my finger and it seals up completely. Running PMC .223

 

[BADUNAME37]

Will it pick up the next round from the magazine if you run the action manually (lock bolt open, then release bolt to slam home on its own)?

 

[ny32182]

Sounds like it is not getting enough gas for one reason or another: 1) Barrel port is the correct size? 2) Gas block port and barrel port lined up well? 3) Gas block locked down well? 4) Gas key on the carrier locked down well?

 

[c172skyhawk2]

Will it pick up the next round from the magazine if you run the action manually (lock bolt open, then release bolt to slam home on its own)?

Yes, it will pick up a round on its own, either by using the charging handle or locking it open and using the bolt release.

Also, I am using new Magpul P-Mags. 2 different ones and same thing.

 

[c172skyhawk2]

Sounds like it is not getting enough gas for one reason or another: 1) Barrel port is the correct size? 2) Gas block port and barrel port lined up well? 3) Gas block locked down well? 4) Gas key on the carrier locked down well?

-I have no idea about the barrel port, this is a new barrel.
-The gas block is lined up well. When I have taken it off I can see residue around the hole and it is in the center perfectly.
-Gas block is locked down very good
-The gas key has no wiggle or play in it, so I guess so

 

[Kwanger]

If the gas system appears to be good and tight with no obvious leakage anywhere, and everything is lined up correctly it could potentially be an undersize gas port. Couple of other things to think about before that though - what weight of buffer are you using? Is the buffer spring standard?

As well - PMC is on the weak side....however, certainly a 16" rifle with a carbine length gas system should have no trouble cycling it as they tend to be pretty harsh when cycling. However, you might try some hotter ammo (such as XM193) and see how that compares.

Which actually brings up another point which is the reverse of what I just said....there is also the possibility that the rifle is overgassed, and is cycling so fast the bolt carrier is outrunning the magazine follower, not giving it enough time to pick up the next round....that would also lead to an empty chamber and click. If this were proven to be the case, a heavier buffer and/or spring would help....if on the other hand it is proven to be cycling weak, going lighter on the buffer is the way.

Is this your only AR? I'd be able to tell weak vs v too fast cycling by feel, but its kinda hard to explain on the net.

 

[TonyAngel]

Does your barrel have a pinned gas block/front sight base on it? Did you put this rifle together from scratch? If so, what parts did you use? What ammo were you running?

Your description sounds like the rifle is short stroking. What sort of handguards are you running. The most common mistake that I see with home builds occurs when you use a free float handguard with a non pinned gas block that is secured by either clamping or set screws. The mistake happens when you don't leave a 1/32" gap between the shoulder on the barrel and the gas block. Although the gas block may be centered, it may be too far towards the back and not letting enough gas through.

 

[TonyAngel]

Sorry, I don't know how I missed all of that info the first time I read your post. Anyway, if you are running a free float guard, check to make sure that you have the gap between the shoulder of the barrel and the gas block.

 

[c172skyhawk2]

Does your barrel have a pinned gas block/front sight base on it? Did you put this rifle together from scratch? If so, what parts did you use? What ammo were you running?

Your description sounds like the rifle is short stroking. What sort of handguards are you running. The most common mistake that I see with home builds occurs when you use a free float handguard with a non pinned gas block that is secured by either clamping or set screws. The mistake happens when you don't leave a 1/32" gap between the shoulder on the barrel and the gas block. Although the gas block may be centered, it may be too far towards the back and not letting enough gas through.

I am running a free float hand guard. I did not have the 1/32" gap, went and adjusted the gas block and it still does not pick up the next round.

 

[c172skyhawk2]

If the gas system appears to be good and tight with no obvious leakage anywhere, and everything is lined up correctly it could potentially be an undersize gas port. Couple of other things to think about before that though - what weight of buffer are you using? Is the buffer spring standard?

As well - PMC is on the weak side....however, certainly a 16" rifle with a carbine length gas system should have no trouble cycling it as they tend to be pretty harsh when cycling. However, you might try some hotter ammo (such as XM193) and see how that compares.

Which actually brings up another point which is the reverse of what I just said....there is also the possibility that the rifle is overgassed, and is cycling so fast the bolt carrier is outrunning the magazine follower, not giving it enough time to pick up the next round....that would also lead to an empty chamber and click. If this were proven to be the case, a heavier buffer and/or spring would help....if on the other hand it is proven to be cycling weak, going lighter on the buffer is the way.

Is this your only AR? I'd be able to tell weak vs v too fast cycling by feel, but its kinda hard to explain on the net.

This is my only AR and I have not handled any other AR (except in the gun stores)

The buffer is a tapco 6 position from MidwayUSA, no idea what kind of spring is in it, I am new to the AR world.
http://www.midwayusa.com/viewProduct/?productNumber=536357

 

[W.E.G.]

Try different ammo before you do anything else.

 

[M1key]

Yeah, Nato pressure stuff like xm193

M

 

[c172skyhawk2]

Try different ammo before you do anything else.

Will stop and get some different ammo when i get a chance.

 

[Mikesull415]

Make sure your barrel is marked 5.56 before you feed any nato rated ammo through it. If it's only marked .223 do NOT use any nato rounds. The barrel isn't made to handle that pressure

 

[1KPerDay]

Make sure your barrel is marked 5.56 before you feed any nato rated ammo through it. If it's only marked .223 do NOT use any nato rounds. The barrel isn't made to handle that pressure

uh....

 

[c172skyhawk2]

Make sure your barrel is marked 5.56 before you feed any nato rated ammo through it. If it's only marked .223 do NOT use any nato rounds. The barrel isn't made to handle that pressure

barrel is good for 5.56, no problems there. now i just need to get some 5.56 and give it a try

 

[TonyAngel]

skyhawk, maybe it would help if you could post a pic. ARs go together pretty easily, but it's also easy to miss something that could render the rifle inoperable. As it stands, I'm still leaning toward and under gas issue or maybe the wrong spring.

Did you get the parts in the form of a kit? If so, what did you get? One thing that I caught just now is that you describe your barrel as being a 16" gov't profile barrel with a carbine length gas system. I'm sure that I'm not aware of all of the barrel options available, but all of the government profile barrels (meaning that the barrel is straight without any cut outs) that I've seen have been cut for mid length gas systems. If you are using a carbine length gas tube with a barrel that has a mid length port, that may be your problem; although if that was the case, I'd be surprised that it was working at all.

Can you confirm that it is a carbine length gas system?

 

[c172skyhawk2]

skyhawk, maybe it would help if you could post a pic. ARs go together pretty easily, but it's also easy to miss something that could render the rifle inoperable. As it stands, I'm still leaning toward and under gas issue or maybe the wrong spring.

Did you get the parts in the form of a kit? If so, what did you get? One thing that I caught just now is that you describe your barrel as being a 16" gov't profile barrel with a carbine length gas system. I'm sure that I'm not aware of all of the barrel options available, but all of the government profile barrels (meaning that the barrel is straight without any cut outs) that I've seen have been cut for mid length gas systems. If you are using a carbine length gas tube with a barrel that has a mid length port, that may be your problem; although if that was the case, I'd be surprised that it was working at all.

Can you confirm that it is a carbine length gas system?

It all went together pretty easy, considering I have never built one or have really zero AR knowledge.

Lower - Bushmaster lower with DPMS internals
Upper - Surplus arms & ammo upper (bought put together with bolt & charging handel
barrel -16 inch m4 profile from sprotsmans guide
stock & buffer - tapco 6 position from midway usa
gas system - yhm low profile gas block, carbine gas tube (tube length little over 9 inches)
handguard - yhm free float quad rail

Handguard removed to show gas system

http://www.flickr.com/photos/65424454@N05/5959351320/

 

[kwelz]

The first thing that sticks out is all of those components are pretty low quality. There is a greater chance of things being out of spec here.

Things to watch for include:
*Gas leak at the block.
*Misaligned Gas block.
*Incorrect Gas port size.
*Loose Gas key.
*Incorrectly aligned Gas Tube.

The list goes on from here. My advice is to get someone to look at it who knows what they are doing.
*

 

[TonyAngel]

Man, this kind of has me scratching my head. If that's an M4 profile barrel, you had it right. It's a carbine length gas system. The first thing is going to be to try some different ammo. I've read of a number of people having problems with some lots of PMC.

If different ammo doesn't help, well, hit the basics. Pull the gas block. Look at the gas port in the barrel. If the gas block is centered properly over the gas port, you should see a little build up of carbon around the gas port. Next, check the gas key on your bolt carrier and make sure that it isn't loose and that you have a good seal. You don't want to see any carbon residue around the gas key. If you do, it's leaking. Now, this may sound silly, but confirm that your rings are good. No offense, but I've seen a few ring sets that came in economy build kits that failed right out of the box. It isn't real common, but it happens.

The proper way to check the rings is to put the bolt into the carrier without the cam pin and see if it falls out. If it falls out, the rings are toast. Personally, I check my rings by assembling the bolt/carrier group, fully extending it and then standing the BCG up on the bolt. If it falls, I change the rings.

You might also want to check your buffer. Some kits come with H or H2 buffers because running them is the "in" thing to do. A combination of a heavy buffer and weak ammo could cause your rifle to eject properly, but fail to feed the next round (short stroke). What is your ejection pattern like? Forward, to the side or to the rear or do the spent cases kind of just fall out of the side?

 

[jad0110]

In addition to trying different ammo Tony makes an excellent point about checking the gas rings. Wouldn't be the first time defective gas rings caused such a problem, but like a gas key that comes loose, it certainly doesn't happen often.

Also, Tony and Kwanger touched on my first thought other than a loose gas key: a buffer that is too light or too heavy. On weaker ammo (including Wolf), the carbine length gas system typically does best with a carbine buffer. But with stronger ammo, many carbines run best with an H (aka H1) or H2. Some even do best with an H3, but that would be pretty unusual.

Pop the rear pin and hinge open the upper from the lower. Take a look at the Buffer itself, the weight that sits inside the buffer tube. If it isn't marked, it is likely a carbine buffer. Otherwise, it will be marked "H1", "H2" or "H3".

 

[c172skyhawk2]

In addition to trying different ammo Tony makes an excellent point about checking the gas rings. Wouldn't be the first time defective gas rings caused such a problem, but like a gas key that comes loose, it certainly doesn't happen often.

Also, Tony and Kwanger touched on my first thought other than a loose gas key: a buffer that is too light or too heavy. On weaker ammo (including Wolf), the carbine length gas system typically does best with a carbine buffer. But with stronger ammo, many carbines run best with an H (aka H1) or H2. Some even do best with an H3, but that would be pretty unusual.

Pop the rear pin and hinge open the upper from the lower. Take a look at the Buffer itself, the weight that sits inside the buffer tube. If it isn't marked, it is likely a carbine buffer. Otherwise, it will be marked "H1", "H2" or "H3".

Where would the buffer be marked? I looked all over the buffer itself and did not find any markings, just wanted to make sure I am looking in the right spot.

The proper way to check the rings is to put the bolt into the carrier without the cam pin and see if it falls out. If it falls out, the rings are toast. Personally, I check my rings by assembling the bolt/carrier group, fully extending it and then standing the BCG up on the bolt. If it falls, I change the rings.

Tested the rings like this and it holds up the entire BCG. It even takes a little pressure from my finger to make it fall.

 

[hja4941]

Another thing to check is the buffer tube itself. It needs to be properly vented to prevent slowing the buffer due to gas pressure build up. When cycled by hand the movement could be slow enough to allow it to vent but when fired it would apply.

 

[Lakedaemonian]

Had the same thing happen to me. My gunsmith (while I was living in Cali) drilled the gas port out a little wider and it worked just fine. I watched him do it. Needless to say I was sweating bullets as it was a brand new Daniel Defense barrel. The little engineer in my head was telling me that he compramised the chrome lining when he did that. (chrome is tough, but brittle) but it doesnt matter to me anymore. I sold the gun 8 months later.

For your situation. I would recommend switching to a better quality of ammo. Sorry but I would rather shoot Wolf than PMC. At least Wolf is made in the same place every time. Then if that doesnt work I'd try changing out your buffer to something lighter. If you still have problems, try a different action spring. (Wolff spring perhaps) If it STILL gives you trouble go back to the barrel, probably have to send it back.

 

[c172skyhawk2]

Another thing to check is the buffer tube itself. It needs to be properly vented to prevent slowing the buffer due to gas pressure build up. When cycled by hand the movement could be slow enough to allow it to vent but when fired it would apply.

Vent hole is free from obstructions. Clean buffer tube. Any thing with the buffer tube I should check other than the vent hole in the end for venting?