AR-15

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No just needs to be straight and have the vent unobstructed. If changing ammunition does not solve the problem, I would check the head space, as this type of malfunction could also be caused by an overpressure. You could also check the spent casings for any signs of to high a pressure, if you don't have head space gauges.
 
hja4941 said:
No just needs to be straight and have the vent unobstructed. If changing ammunition does not solve the problem, I would check the head space, as this type of malfunction could also be caused by an overpressure. You could also check the spent casings for any signs of to high a pressure, if you don't have head space gauges.
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Headspace checks ok, it closes on the "go" gauge and does not close on the "no go" gauge. What are some signs of overpressure on the spent casings? Just want to double check stuff I can
 
jad0110 said:
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".
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Alright, stopped by and picked up some 5.56 and ran 10ish rounds through the gun. Gun cycled but barely. It would pick up the next round, most of the time, but never would lock open on the last round.
 
TonyAngel said:
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?
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When it does eject the shells they are at my 4 o'clock or so and 5ish feet away.

When i do shoot it and it does not eject the round I can hear the buffer spring, where as when it does eject the round I cannot hear the spring.
 
I would look to the gas port as well, does anybody know what the spec is for that barrel?
A welding torch tip cleaner will get you pretty close to sizing the hole (just find the one that fits the best and mic it) if it is out of spec either send it back or drill it out.
 
X-Rap said:
I would look to the gas port as well, does anybody know what the spec is for that barrel?
A welding torch tip cleaner will get you pretty close to sizing the hole (just find the one that fits the best and mic it) if it is out of spec either send it back or drill it out.
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Took off the gas block and measured. I get 1/16 inch, or .0625 on the gas port, no wiggle room.

Just waiting to hear if this is in spec.
 
PMC ammo is very reliable so I doubt it's your ammo.

But because you haven't told us precisely what parts you used in your build (part numbers, where you bought them, etc), here are the things I'd check first :

0) The mag release is interfering

1) The hammer is mis-shapen, over-sized, or is otherwise out of position and is interfering with the magazine feed.

2) The trigger is interfering with the bolt during the compression stroke.

3) The action spring is too heavy and is not allowing the bolt to compress it enough to allow a round to be fed into the chamber.

4) The buffer is too heavy for the bolt.

5) The bolt is binding in the upper on the compression stroke. Look for excessive wear on the BCG rails or inside the upper receiver.

Items 1 and 2 above could also be caused by an incorrectly drilled lower receiver.

BTW, does the safety appear to work normally?

If the buffer or action spring are too heavy, a standard AR-15 bolt won't reliably compress the spring enough to allow the next round to feed out of the magazine. I have a full-auto BCG in my scratch built, and have a heavier buffer (H2) and spring (Sprinco Blue) to compensate. My other AR has a semi-auto bolt and a standard buffer/spring as a result.

Regarding lubrication, I put little axle grease on the carrier rails, and a drop of oil on the bolt gas rings. Other than a drop of oil on the trigger pins every once in a while, that's the extent of my lubrication.
 
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In addition to other suggestions-

Check the gas key on the BCG. If the bolts are loose or the mating surfaces damaged it will leak.

Check the rings on the bolt (It does NOT matter if the gaps in the gas rings line up or not). If the rings are worn, wrong size or damaged, they will leak
 
Are you getting doubles or failure of the bolt to lock back if only shooting a single round?
I would check all the springs in the trigger group.
 
C-grunt said:
Spec is .063. Not sure if the 5/1000th is gonna make a difference.
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Yep...that's in spec....that 5/1000th is so tiny the error could be in the gauge, bit of soot whatever. If it was a few 100ths, you'd know there was an issue, but as is...this is not your problem.
 
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.
Click to expand...

????????
Don't think thats the case. From what i've seen the only reason there is a vent in the buffer tube is a liquid drain....not to vent "gas" out. The clearance between the buffer and the tube is plenty big to let air excape around it.

To the original OP it could also be the size of the vent holes in the side of the carrier. If they are oversized it could be allowing more gas to exhaust. This happens pretty close to the same time that the bolt unlocks from the extension.
 
X-Rap said:
Are you getting doubles or failure of the bolt to lock back if only shooting a single round?
I would check all the springs in the trigger group.
Click to expand...
Getting failure to lock open on last shot, failure to strip the next round and feed it and sometimes a failure to eject the casing. Seems like the bolt is only coming about half way back. Rounds feed fine when actuating the bolt by hand.
 
Sounds like my buddy's first AR build...

IIRC, he fixed it by replacing the gas rings on the bolt. Does the bolt hold up the weight of the carrier when stood on its face end? Even if it does, the gas rings are a cheap replacement.
 
Waywatcher said:
Sounds like my buddy's first AR build...

IIRC, he fixed it by replacing the gas rings on the bolt. Does the bolt hold up the weight of the carrier when stood on its face end? Even if it does, the gas rings are a cheap replacement.
Click to expand...

Yes the bolt does hold the carrier when stood on the bolt face. It even takes some pressure to push it down. This is the only Ar bolt I have messed with but it moves freely (does not bind) and smoothly.
 
Could any of yall measure how many pounds it takes to pull back the charging handle. I just wonder if my buffer spring is too strong. Just sitting here thinking and I have no ar's to compare to
 
I'm not sure of the weight but I've had good luck with sprinco's white power spring. It doesn't take much effort to cycle.

Sent from my LG-P999 using Tapatalk
 
ok most everything has been covered here. but 1 thing that i ran into with a model1 upper the gas key....and i'm not talking about a loose gaskey.i had 1 the inside diameter was way undersized. can't remember how much it was.but i'm thinking your gaskey may be over sized. or the end of the gas tube that mates with the gas key is undersized?i' don't know the specs off the top of my head.look them up and check it.i know this is a shot in the dark but.....everything else i can think of has allready been covered
 
Have you checked the brass after firing to see if there are any signs of something wrong with the chamber?
 
HOLY DIVER said:
ok most everything has been covered here. but 1 thing that i ran into with a model1 upper the gas key....and i'm not talking about a loose gaskey.i had 1 the inside diameter was way undersized. can't remember how much it was.but i'm thinking your gaskey may be over sized. or the end of the gas tube that mates with the gas key is undersized?i' don't know the specs off the top of my head.look them up and check it.i know this is a shot in the dark but.....everything else i can think of has allready been covered
Click to expand...
How could I check this easily? Take the gas tube and bolt carrier out and mait them together outside the gun and check fit?
 
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