AR Help Please

[kahrk-9]

Thanks in advance.
I bought a lower and added a 9mm conversation to it, ran some mags; all good.
Added a can ran some mags; all good.
Next trip I start having FTF on last round.
Disassembled, cleaned lubed different mags and it gets steadily worse until it won’t even feed half the time. I send off the 9mm conversation for warranty and get a different upper in 5.56.
Go to the range and it won’t feed off multiple mags.
Go home and try two other uppers with safety rounds and have the same result.
I put the second upper mentioned (556) on a different lower and it feeds the safety rounds.
It seems the issue is the lower but am hoping you can tell me how to troubleshoot. I’m thinking measure the height of the ammo sticking up from the receiver against other receivers. If that’s the issue I’m thinking maybe mag release or receiver itself.

Please tell me there is a simple fix.

 

[Letfreedomring]

It would help to know what conversion you're using. Since it ran fine at the beginning and steadily started getting worse I would think the maybe the adjustment screws for the adapter were backing off causing mag to sit too high in chamber interfering with bolt. Also what buffer and spring are you running? Blow backs need heavier buffers. I'm in process of putting together an AR-45 and it supposedly needs an 11oz buffer.

 

[kahrk-9]

It would help to know what conversion you're using. Since it ran fine at the beginning and steadily started getting worse I would think the maybe the adjustment screws for the adapter were backing off causing mag to sit too high in chamber interfering with bolt. Also what buffer and spring are you running? Blow backs need heavier buffers. I'm in process of putting together an AR-45 and it supposedly needs an 11oz buffer.

I was running the one from Macon Armory. I’m using the standard AR buffer (3 oz?). I feel like it did better with the 9mm than the 5.56 upper though, so it’s hard for me to blame the 9mm conversion. With 5.56 the bolt slides completely over the rounds with multiple uppers and mags.

 

[dlbleak]

Didn’t we have a member recently that had a similar issue? There was a specific pin or spacer that had to be used or removed? Sorry for being so vague, just going off a weak memory!

 

[Shadowrider]

Check your mag catch. ETA: Also the bolt catch in 9mm conversions are pretty notorious for breaking with 9mm conversions due to the increased weight of the bolt and buffer. Look at that too.

 

[kahrk-9]

I got it figured out. Thanks all!

 

[montesa]

I got it figured out. Thanks all!

You’re supposed to tell us what it was.

 

[kahrk-9]

You’re supposed to tell us what it was.

I’m embarrassed to say but if I’m pushed to it… I had the pistol buffer in it so the carrier group was not going back far enough chamber.

 

[montesa]

I’m embarrassed to say but if I’m pushed to it… I had the pistol buffer in it so the carrier group was not going back far enough chamber.

Glad it works!

 

[Mr.Glock]

Honest mistake!