A bit of help with this malfunction.

[kwelz]

I am pretty sure I know the problem but I wanted to ask people far more intelligent than I am.

Today I took my SBR to get it sighted in before my LAV class. The range is an indoor range with more rules than common sense so I was not able to do much to diagnose issues on site.

3 or 4 times over the course of the day I had the bolt slide over the top of the round and trap it between the bolt and the feed ramps. I thought it may have been mags since I was using a couple USGI 20s, however my friend had no problems with the same mags and I did have the same problem with my single Lancer 20 rounder.

The gun is the following.
Daniel Defense 10.3 inch LW barrel, Upper and Bolt. Colt Lower with a H buffer.
Ammo was PMC Bronze 55 grain.

I am sure it is something pretty basic but I wanted to run it by the smart people.

Thanks.

[nimdabew]

From waht you said, it sounds like the carrier speed is too fast and the magazine spring isn't acting fast enough before the BCG slams home. Do you have an H3 buffer and maybe an extra power spring laying around so you can swap weights around to change the buffer weights?

[eternal24k]

I am having a little bit of a hard time understanding the problem when you state that the "bolt [slides] over the top of the round and trap it between the bolt and the feed ramps"

failure to feed? Does the round leave the mag?

What's the history of this rifle?
I would not take a gun to a class unless I knew it was reliable, hopefully you can fix this and put some serious rounds down range before the class, you don't want to be "that guy"

[5pins]

Is this the first time you have shot PMC 55gr? My experience with it that it a little under powered. When I chroned some the average velocity was quite a bit less then most.

[Redhat]

Try different ammo. Is it possible the bolt is not moving far enough to the rear to pick up the cartridge?

[Clint]

The first thing to do is check for lockback on single rounds.

This should narrow it down to short stroking or overspeeding.

I believe the DD use small gas port sizes to run properly with full pressure 5.56 ammo.

That PMC bronze .223 is likely the issue.

[kwelz]

Is this the first time you have shot PMC 55gr? My experience with it that it a little under powered. When I chroned some the average velocity was quite a bit less then most.

Yep ran thousands of rounds of it.

I am having a little bit of a hard time understanding the problem when you state that the "bolt [slides] over the top of the round and trap it between the bolt and the feed ramps"

Correct. The round is pushed a bit forward. Enough to get onto the feed ramps but the bolt is sliding over the top of it and jamming it in there.

failure to feed? Does the round leave the mag?

Only partially

What's the history of this rifle?

Well it is sort of old and sort of not. All components except the stripped upper were together before and ran through a VSM lass last month. I had to replace the upper due to some other issues not related to the function we are talking about here.

I would not take a gun to a class unless I knew it was reliable, hopefully you can fix this and put some serious rounds down range before the class, you don't want to be "that guy"

No doubt. Hence the range time today and going back out tomorrow to figure this out.

I will switch out to some of my XM193 I have on hand to see if that is any better.

[eternal24k]

gotcha. I think Clint nailed it

[kwelz]

gotcha. I think Clint nailed it

Yeah. thinking along the same lines. Originally I was thinking the bolt was moving to fast but it is also possible that it is short stroking. I just hadn't thought about that since the ammo has worked in the past.

I am just going to have to put a few more rounds down range tomorrow to troubleshoot.

[Redhat]

You might also check your carrier key and gas tube