ar-15 bolt hold back not reliable

[41magsnub]

new self built ar-15 lower with factory assembled upper:

Tactical Innovations lower
DPMS lower parts kit
BCM M4 stock with carbine buffer and spring
BCM light weight middy upper + daniel defense BCG


With an empty magazine inserted the bolt hold back is rock solid, could not work better. The only way to make it release is with the button.

Without a magazine, it takes a few tries to get it to catch and even the slightest shake of the rifle will release it. It is not like every other AR-15 and M16 I've handled where they hold pretty well but a good slap to the butt stock will release it. This one it just takes jiggling the rifle a bit.

What I have tried:
Swapped BCG's with another AR-15, same issue.
Swapped buffers and springs with another carbine length Stag AR-15, same problem
Swapped the uppers between the two AR-15's. When swapped both work as expected.

Before I go punching out roll pins and finding another bolt catch and springs.. any other ideas? I'm not sure why the problem isn't still there with a different upper/bolt on it yet the problem doesn't then occur on the other lower with the upper from this rifle.

 

[Ramone]

I'd suspect a minor fitment issue between upper and lower if none of the following apply, or perhaps in combination with one of the following:


Do you have a B.A.D. lever on it?

are you SURE the correct detent is installed the right way around?

Maybe a bit of forgein matter is in there?

 

[kwelz]

DPMS lower parts kit

This is probably your problem. DPMS LPKs are usually pretty iffy. Oversized roll pins, out of spec parts, etc.

 

[41magsnub]

Good call on the crappy parts kit. I just bought another Stag LPK locally and rebuilt the lower (buggered up the finish a bit but I'll live). 100% function. Things are over all a bit smoother.

No BAD lever installed.

 

[kwelz]

Really glad you got it fixed. Some Alumiblack will fix the marks on the lower. I have built no less than 20 lowers and I still sometimes ding them up, especially the area around the bolt hold open. In fact I just borked up a Noveske Gen2 lower there last week.

In a number of those early builds I tried using DPMS LPKs. I had to do enough finish work that I feel like DPMS should be sending me a check.

 

[41magsnub]

Thanks! looking into that. I've asked Bravo Company for a refund on the DPMS LPK and a shipping label if they actually want the bad one back. I'm sure they will take care of me.

There were some other issues.. the magazine release button was really "grabby" and I could make it hang up if I pressed it at the right angle. Roll pins were nearly unstartable even with the fancy roll pin starter tools.