9mm SBR suppressed FTF last round in magazine

[Willy Leadwell]

5.5" barrel running a JP silent spring and an octane 9. Fails to feed the last round of every magazine. 31 rounds run flawlessly then that last round just doesn't quite make it up and into the chamber. My first thought is that it's a magazine issue, but all I currently have is ASC mags for it. Just wanted to see if there were any factors that could cause this, or if there was a known issue with the ASC magazines.
@PewPewPewCo

Oh, and I got the same result with 115gr. and 147gr.

 

[Mac11FA]

Are you having the problem with more than one mag? I know the action can get pretty dirty when shooting suppressed and it may be one cause. I had the issue with the M11 on all my sten mags and ended up stretching the springs a little to help. The bolt can't be short stroking as the problem appears to happen whether using full power or reduced power 9mm.

Also, new mags do take some time to break in as well.

 

[boss_hawg]

Does this happen with Metalform mags?

 

[Willy Leadwell]

Are you having the problem with more than one mag? I know the action can get pretty dirty when shooting suppressed and it may be one cause. I had the issue with the M11 on all my sten mags and ended up stretching the springs a little to help. The bolt can't be short stroking as the problem appears to happen whether using full power or reduced power 9mm.

Also, new mags do take some time to break in as well.

I currently only have 3 ASC mags and yes, all three of them did the same thing. She was clean as a whistle and bleeding oil. I plan to add many more mags, but wanted to see if there was a better option out there. When I built it and ordered these availability was extremely limited.

 

[Mac11FA]

I currently only have 3 ASC mags and yes, all three of them did the same thing. She was clean as a whistle and bleeding oil. I plan to add many more mags, but wanted to see if there was a better option out there. When I built it and ordered these availability was extremely limited.

I understand that. Hell, if the first 31 rounds run without issue, try just loading 30 rounds and see how it does.

 

[Willy Leadwell]

I understand that. Hell, if the first 31 rounds run without issue, try just loading 30 rounds and see how it does.

Well, after I shoot the first round, the mag is loaded with 31 rounds.

I don't think that the problem is that it fails to feed the 32nd round, but that it fails to feed the last round in the mag.

 

[Willy Leadwell]

When I bought ASC mags for my AR10 I had to take measurements from some Pmags and break out the Dremel to modify the ASC mags to get them to feed at all. So my first thought was that once again, the ASC mags are junk, but in this case why would 31 rounds feed perfectly and just the last one fail?

I'll just wait for a few different mags to show up at my door and try it again.

 

[Mac11FA]

When I bought ASC mags for my AR10 I had to take measurements from some Pmags and break out the Dremel to modify the ASC mags to get them to feed at all. So my first thought was that once again, the ASC mags are junk, but in this case why would 31 rounds feed perfectly and just the last one fail?

I'll just wait for a few different mags to show up at my door and try it again.

There are just some mysteries that never get revealed!

 

[boss_hawg]

Could be that the bolt is somehow catching the mag's round follower and retarding its momentum. Also, do you have other 9mm buffer setups you could try? I remember folks posting that the JP setup can be finicky.

I would try to cheapest solution first. PSA sells their branded mags which are metalforms and worth every cent of their $25 cost.

 

[Willy Leadwell]

There are just some mysteries that never get revealed!

I'll never let a malfunctioning gun get the better of me. That's how I ended up on the forums to begin with. There's no problem that a little redneck ingenuity and the internets can't solve.

 

[freedom]

If you load one round, will it feed?

 

[Willy Leadwell]

Could be that the bolt is somehow catching the mag's round follower and retarding its momentum. Also, do you have other 9mm buffer setups you could try? I remember folks posting that the JP setup can be finicky.

I would try to cheapest solution first. PSA sells their branded mags which are metalforms and worth every cent of their $25 cost.

I'm gonna get some more mags here ASAP. That's kind of what I was wondering. I built it with the JP and it's the only one I have. If other mags do it, I'll look there next.

 

[Willy Leadwell]

If you load one round, will it feed?

If I load one round in a mag and charge it yes, it will feed.

 

[Willy Leadwell]

Could be that the bolt is somehow catching the mag's round follower and retarding its momentum. Also, do you have other 9mm buffer setups you could try? I remember folks posting that the JP setup can be finicky.

I would try to cheapest solution first. PSA sells their branded mags which are metalforms and worth every cent of their $25 cost.

I swear when I was building and ordering parts I remember reading that PSA mags were ASC. Has something changed or am I making up new memories?

 

[boss_hawg]

I swear when I was building and ordering parts I remember reading that PSA mags were ASC. Has something changed or am I making up new memories?

http://palmettostatearmory.com/psa-9mm-smg-magazine.html

States that they are made by Metalform in the description. They are identical - other than the PSA logo - to other Metalform mags that I own (I have both). Sometimes, PSA will have these marked down a buck or two which is a great time to buy en masse.

 

[Willy Leadwell]

http://palmettostatearmory.com/psa-9mm-smg-magazine.html

States that they are made by Metalform in the description. They are identical - other than the PSA logo - to other Metalform mags that I own (I have both). Sometimes, PSA will have these marked down a buck or two which is a great time to buy en masse.

I see that, but was that the case a year ago?

 

[boss_hawg]

I bought my PSA mags when they hit the market. They did sell ASC mags too maybe but I went with these.

if I recall, when they sold asc mags they were clearly labeled as such

 

[rOmiLaYu]

Could be that the bolt is somehow catching the mag's round follower and retarding its momentum. Also, do you have other 9mm buffer setups you could try? I remember folks posting that the JP setup can be finicky.

I would try to cheapest solution first. PSA sells their branded mags which are metalforms and worth every cent of their $25 cost.

This would be my guess. Something about the follower and the bolt riding it and slowing down. Are there any abnormal wear marks on the follower?

 

[Willy Leadwell]

This would be my guess. Something about the follower and the bolt riding it and slowing down. Are there any abnormal wear marks on the follower?

No, I don't see anything unusual. I'm gonna get a few mags ordered, run it a bit more and see what happens.