I recently finished my build, took it to the range today. Out of 50 rounds I had 2 FTF. It’s also not locking back on an empty mag. I’m not sure if it’s under/over gassed, the mag has a problem or if it’s just the ammo. I was shooting American Eagle .223. I am including pictures of the jam below and hopefully someone can help.
Need more info. Buffer weight? What brand are the components? Could be under gassed. Could be too heavy of buffer…
Its a carbine buffer. And it’s an Anderson upper and a Radical Firearms barrel.
Need more details. Post a complete list of the parts.
Upper:
Anderson Upper
Radical Firearms 16" 1:7 twist midlength gas
Radical BCG
MI gen2 T series quad rail
YHM low profile gas block
Lower:
Aero lower
CMMG LPK
DS Arms buffer assembly with carbine buffer
Magpul CTR
I believe that Radical could be the issue. I have recently been hearing of issues with some of their stuff. You should also be using an H buffer at a minimum.
Well the bolt is not locking back now on an empty mag with the carbine buffer. So wouldn’t an H buffer exacerbate the problem?
I’m simply telling what the standard is. Across the board virtually any PROPERLY ported barrel and or assembled upper should be able to function with an H buffer. Whether it is a Colt 6920, BCM Midlength, SIONICS, etc…
In your current state of malfunctions you are probably under gassed. Who assembled the upper? Is the gas block aligned correctly? Gas key tight on the carrier? I would start by looking for gas leaks.
check that the hole in the gas tube lines up with the hole in the gas block too. One of the last gas tubes I got didn’t line up and I had to drill it out.
Domino:
I believe you accidentally used the “report a post” feature button to post a public reply. Please remember that when you want to answer a public question, use the “Reply to Thread” button on the lower left corner of the bottom of the screen.
Thanks.
This is a good place to start. What type of LP Gasblock is the YHM? Is it a clamp-on or set screw? If you are using a set screw GB, is the barrel dimpled for the set screw? Do you have the GB pushed all the way up against the barrel step?
How many different mags are you using? Is this malfunction only happening with the same mag?
It is the set screw type, and the barrel does have a dimple for one of the screws, and I do have it pushed back all the way to the step. And I only have one mag, but I was thinking about picking another one up to see if thats the problem.
I would measure the port location from the step on the barrel (distance), then measure your gas block. Most the gas blocks I’ve used don’t always sit against the step, around .015-.030 away. Your barrel might not be dimpled in the right location either. I would check this first or try some different mags.
Get a new mag or two or ten, for sure. What ammo were you shooting?
OP: The term “jam” is best replaced with “malfunction”. Then you describe what type of malfunction you are having.
In this case, it’s a bolt over base Failure To Feed malf, where the bolt carrier group is not traveling back far enough to the rear-something you were able to establish by determining if it will lock back the BCG on the last round with a mag in the weapon.
That is almost 100% an under-gassed condition. Since you installed the low profile gas block directly abutted to the shoulder on the barrel at the shoulder/journal junction, I suspect that you have a misaligned gas block, which is choking the port, and causing your issue.
This is one of the most common causes of under-gassed build project look-alike AR15’s today, because very few people know about the original gas block/Front Sight Base + handguard cap dimensions that most barrels have.
As has been mentioned, anyone assembling one of these needs to measure their gas port location from the rear end of the block to the center of the port.
Then measure the distance from the barrel shoulder to the center of the gas port on the barrel. I use calipers for this, and I use the end of the calipers as a protrusion gauge for the gas block measurement. Most of the time, they will not coincide, so you need to step the gas block off of the shoulder a considerable amount.
The reason for this again is because AR15 barrel profiles are usually set up to accommodate the handguard cap, which is used less and less nowadays with the predominance of free-float handguards.
Reread original post.
BCG looks pretty dry also. Probably isn’t helping the situation.
Check gas rings for gap alignment, lube the gas rings, inspect carrier key and gas block for signs of leakage.
Exactly what is alignment gap in gas rings?