I need you help to figure out what is wrong with my latest build. I have 3 lowers sitting around and have decided to finish them up. 1 PSA lower and 2 RRA lowers. I purchased 3 DPMS lower part kits and had a local gunsmith install them. I purchased 1 PSA complete upper and 2 Colt complete uppers.

1. PSA lower + PSA upper = OK
2. RRA lower1 + Colt Upper 1 = OK
3. RRA lower2 + Colt Upper 2 = Not OK. Last round bolt hold open will NOT work. Either on EMPTY mag or manually pressing bolt catch (without mag).

All 3 uppers worked with PSA lower and RRA Lower1.
NONE of the 3 uppers will Hold Bolt Open on RRA Lower2.

So I figured the Bolt Catch of RRA lower2 might be out of spec. I went to a local gun store this morning and purchased a different brand Bolt Catch and replaced RRA Lower2. Tested all 3 uppers. Last Round Bolt Hold Open still will NOT work on the RRA lower2. Even with the NEW bolt catch, spring plunger and pin, still will NOT work.

Any ideas/suggestions? Is there something wrong with the RRA lower2? If so, what could it be?

(I have NOT test fired any of the 3 rifles yet).

Have you tried it with other empty mags? Does it catch when you operate the bolt catch manually with no magazine in place?

We're probably gonna need a pic of the lower receiver(no upper) showing the bolt catch area with bolt catch raised on an empty mag as well as lowered in the resting position.

Hi m499. I tried with Pmag and Original Colt metal mags. Also tried pushing the bolt catch manually (without any mag). It will not hold the bolt open.

This message has been edited. Last edited by: ador,

I don't see anything weird in the pics other than your bolt catch looks like it's a non-standard "extended paddle" version of some sort but that shouldn't necessarily cause an issue.

I'd do a visual side-by-side comparison with one of your other lowers that you know works. Check bolt catch travel on both. Measure how high each rises out of the receiver when engaged. Seems like there would be an obvious difference when you compare the two.

When the charging handle is pulled all the way to the rear is the face of the bolt about even with the rear of the ejection port?
Should have about .250" gap between the bolt and bolt catch.

If the BCG is pulled past the bolt catch and it's going over the top of it then it may have a bolt catch pin hole that's off.

The pics are kinda dark but that does not look like a mil-spec bot catch lever...it appears to have some kind of extended lower portion that extends beyond the sides of the bolt catch channel. Is it possible that the extended sides of the lower portion of the lever are bottoming out against the side of the lower before allowing the catch to rise far enough to engage the bolt?

It also looks like your gunsmith didn't get the pin in all the way...but that's more of a cosmetic issue.

I'd swap that bolt catch out for a mil-spec part before blaming the lower.

The original DPMS bolt catch I replaced did not have the paddle. The new one I bought today with the paddle stated "mil-spec" on the packaging, although with that lower paddle. I really don't care which one I end up using. I just want it to function properly.

OK. I just compared the 2 RRA lowers with the Colt Uppers. On the problematic lower (RRA2), the bolt DO NOT retract all the way back. (it sticks out about .5 inch and NOT flushed to the rear of the ejection port). This is a far as it can retract. That is why the bolt catch is NOT catching the bolt. The bolt catch itself is NOT THE PROBLEM.

I compared the 2 lowers. They have the same exact buffer tube. The recoil buffer the same length. The only thing different is that the spring of the problematic lower is a bit longer (about 2 circles longer). Could that cause the bolt to NOT fully retract?

It takes like 30 seconds to do a swap on this issue. pull the working buffer and spring and put it in the problematic lower and see what happens.

I did that just now. No difference. It felt like something is preventing the bolt from retracting all the way inside the buffer tube.

quote:

Originally posted by hrcjon:
It takes like 30 seconds to do a swap on this issue. pull the working buffer and spring and put it in the problematic lower and see what happens.

Are you using a rifle spring in a carbine tube?

If its not a rifle spring in a carbine tube, not sure what else it could be... Shine a light into the buffer tube - is there anything stuck in there?

Bolt catch is OK.
Is the grip screw interfering with the bolt?
Is there a problem with the detent that holds the buffer in place?

When I tested the working buffer spring and recoil buffer from the working lower (RRA lower1) onto the problematic Lower2, it had the same issue. I can't pull the charging handle and bolt far enough for the bolt catch to hold the bolt. So that eliminates the buffer spring/recoil buffer as the cause of the problem.

I looked down the buffer tube last night using a flash light. I see some black looking tar/oil. Not sure what it is. I will do some more probing when I get home today.

No issue with the detent that holds the buffer in place. I will investigate some more later today. I may end up getting a new buffer tube this weekend to see if that will solve the problem. I will also check the grip screw as SIGfourme suggested. Thanks for the responses.

Have you considered swapping the buffer tube with another?

You tested the non-working buffer and spring in one of the rifles that the bolt catch works on, correct? I'm thinking a bent, out of true or out of spec receiver extension or the threads for the reciver extension where drilled off center.

This message has been edited. Last edited by: CD228,

ador - Did you ever figure out what the issue was with your lower??

"Enquiring minds want to know..."

Not yet. I was out of town for over a week. Just got back stateside last night. Will work on this issue again this weekend.

quote:

Originally posted by m499:
ador - Did you ever figure out what the issue was with your lower??

"Enquiring minds want to know..."

Unless I missed it you didn't say how the lowers are configured. A1, A2, or carbine stocks and buffer tubes? I had this exact problem, and it was because I used an A2 buttstock screw instead of an A1 sized screw.The same thing can happen with rifle parts in a carbine in a collapsible stock is being used.

This message has been edited. Last edited by: SgtGold,