My son built an AR with a BCM BCG and Complete upper. He also put in a LPK from Stag. It was his first build. He lives in Tampa, me in NE Ohio.

The problem is that about every 10 Rds or so he has no ignition of primer. I told him it might be hard primers. He’s using Federal 55gr from WW. This is the second time he’s shot it with same results. Also, what is the correct buffer for ML system?

What could be going on? Ammo?? Buffer?? Firing Pin??? I told him to try different ammo next time. But thought you guys could put more light on the subject. He will be reading this for your suggestions. Thanks.

Make sure he put the trigger spring in the correct way.

The buffer and spring are matched to the receiver extension (buffer tube) type, either collapsible or rifle. It has nothing to do with the upper gas system. A fairly common problem with a home built lower is getting the hammer spring on wrong. I would check that first.

Hammer spring backwards. Weak hammer spring, there are some junk ones out there that are bad even new. Not enough firing pin protrusion. To much headspace. All come to mind.

If his trigger pull feels kinda mushy, but light in pull weight, and feels a bit like a 3-4 lb two stage...the spring is the culprit. I did this on last build, too many distractions and in a rush, I goofed it up.

quote:

Originally posted by Jelly:
Hammer spring backwards. Weak hammer spring, there are some junk ones out there that are bad even new. Not enough firing pin protrusion. To much headspace. All come to mind.

This is about what I'm leaning towards, too. Especially hammer spring related.

What lower is he using?

quote:

Originally posted by Scurvy:
Make sure he put the trigger spring in the correct way.

Yup..


Pretty much all the guys in this thread already nailed it.


An incorrectly installed hammer spring will result in light primer strikes. (it is a very easy mistake to make)

Have him take an in focus picture of the inside of his lower, especially around the hammer.

Post it here and we can either confirm or rule this out.

quote:

Originally posted by IndianaBoy:

quote:

Originally posted by Scurvy:
Make sure he put the trigger spring in the correct way.

Yup..


Pretty much all the guys in this thread already nailed it.


An incorrectly installed hammer spring will result in light primer strikes. (it is a very easy mistake to make)

Have him take an in focus picture of the inside of his lower, especially around the hammer.

Post it here and we can either confirm or rule this out.

I'm speaking from experience...it's a very easy mistake to make.

When the hammer spring is installed backwards/incorrectly, the trigger pins work their way out of the lower every dozen shots or so as well. Very easy diagnosis, when you see some guy on the range and his pins are walking out.... his hammer spring was installed incorrectly.

For a 16 inch mid-length gas system, if you have a A2 style stock, then you use an A2 style rifle buffer. If he has the collapsible carbine stock (more likely), then he can use a regular 3.0 ounce carbine buffer, or a 3.7 ounce H buffer, or a 4.6 ounce H2 buffer typically.

H buffer is a good standard recommendation.

If he has a 14.5 inch mid length, he might need to run a standard 3.0 ounce buffer. I have a very early BCM 14.5 inch mid length, that is under gassed. It doesn't work right with an H buffer, but functions perfect with a standard buffer. My gun is a very early model, and I believe they increased the gas port size on the later guns.