Can't get my mpx to cycle subs.

[ARCHIVED THREAD] - Can't get my mpx to cycle subs.

Posted: 10/16/2016 10:32:16 PM EDT

I'm kind of stuck here, I used coated hard cast bullets first, but I figured it didn't like the shape of them, so I ordered some regular round nose bullets. Started low, around 900fps with poor results, worked all the way up to over 1050fps and the cases started bulging, but still wouldn't reliably cycle and eject the brass. Cycles supers all day, but can't get through 5 of my subs without a failure, I'm unsure of what to do. I'm using a 6" barrel and an Octane 9 suppressor.

Posted: 10/16/2016 11:00:50 PM EDT

[#1]

6" barrel with 147 GR subs no problem here.

Posted: 10/16/2016 11:11:05 PM EDT

[#2]

I've probably got 1,200+ through mine without a hiccup. Using and 8" barrel though. Griffin Armament Revolution 9 in the K configuration and a 3 lug adapter.

I use 147gr round nose. Have used both Berry's and Frontier bullets. 4.4gr of Silhouette, 1.155 OAL. I haven't chrono'd them but loading manual says they would be about 900fps.

Posted: 10/16/2016 11:45:32 PM EDT

[#3]

Dang....I've used the coated cast bullets a lot in my G34 and G17L suppressed with no issues at all. But I can't get the mpx to work with them or the round nose fmj for some reason. The only thing I've changed is the 6" barrel and a Geissele SD-E trigger.

Posted: 10/17/2016 12:35:10 AM EDT

[#4]

Xtreme 147 plated over a middle book load of titegroup, as well as Xtreme plated 124 over a low book load of titeWAD both cycle beatifully and are subsonic for me. The titeWAD load won't cycle any glock I've tried it in.

Posted: 10/17/2016 1:28:24 AM EDT

[#5]

I'm using the 147gr everglades plated bullets and universal powder. I can't remember the exact charges, but I think I started down around 3gr, and worked up from there.

Posted: 10/17/2016 7:05:07 PM EDT

[#6]

I had problems with 147's/subs. Talked to Sig, they advised 200-300 rounds of supersonic 115's or 124's. I cleaned and lubed it then mag dumped a few hundred clean and lubed again and have had zero problems with 147's since.

Posted: 10/17/2016 7:06:12 PM EDT

[#7]

Have you cleaned you piston assembly? Maybe its getting fouled up to much?

Posted: 10/17/2016 7:15:22 PM EDT

[#8]

Quote History

Quoted:
I had problems with 147's/subs. Talked to Sig, they advised 200-300 rounds of supersonic 115's or 124's. I cleaned and lubed it then mag dumped a few hundred clean and lubed again and have had zero problems with 147's since.

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I'm guessing it has about 500 supers through it right now, and I've already cleaned and lubed once. I could just keep trying and maybe at 1000 it might work.

If Glock made a carbine it would work with everything right out of the box

Posted: 10/17/2016 7:25:52 PM EDT

[#9]

Can or no can?

Posted: 10/17/2016 8:03:19 PM EDT

[#10]

Quote History

Quoted:
Have you cleaned you piston assembly? Maybe its getting fouled up to much?

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I read your post and decided it was time to give that a try, I hadn't taken it apart yet because I figured if it was working with supers then subs shouldn't be a problem either, but I guess I dont have any science to merit that. So I took it apart and it was a bit tough to get apart and it was definitely dry in there. Nothing too heavy as far as residue, but I cleaned it out and sprayed it with CLP and went back together.

First round immediately stove piped, cleared it and fired 14 rounds perfectly. I'll fire the rest of the batch I have loaded and go from there. I didn't think after a few hundred rounds it would be enough to make the gas system useless, that seems to be it though.

Posted: 10/17/2016 8:04:00 PM EDT

[#11]

Quote History

Quoted:
Can or no can?

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Always fired with a can. Loud noises scare me

Posted: 10/18/2016 4:40:23 PM EDT

[#12]

Quote History

Quoted:

I read your post and decided it was time to give that a try, I hadn't taken it apart yet because I figured if it was working with supers then subs shouldn't be a problem either, but I guess I dont have any science to merit that. So I took it apart and it was a bit tough to get apart and it was definitely dry in there. Nothing too heavy as far as residue, but I cleaned it out and sprayed it with CLP and went back together.

First round immediately stove piped, cleared it and fired 14 rounds perfectly. I'll fire the rest of the batch I have loaded and go from there. I didn't think after a few hundred rounds it would be enough to make the gas system useless, that seems to be it though.

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Quote History

Quoted:

Quoted:
Have you cleaned you piston assembly? Maybe its getting fouled up to much?

I read your post and decided it was time to give that a try, I hadn't taken it apart yet because I figured if it was working with supers then subs shouldn't be a problem either, but I guess I dont have any science to merit that. So I took it apart and it was a bit tough to get apart and it was definitely dry in there. Nothing too heavy as far as residue, but I cleaned it out and sprayed it with CLP and went back together.

First round immediately stove piped, cleared it and fired 14 rounds perfectly. I'll fire the rest of the batch I have loaded and go from there. I didn't think after a few hundred rounds it would be enough to make the gas system useless, that seems to be it though.

If you never taken it apart, it may just have been lacking in proper lubrication from factory.
I always take my guns apart when I first get them (any part that is expected to be cleaned periodically) and clean/lube to make sure it start its break-in well lubed, and to fully understand what it will take to break them down, should it ever be needed in the field.

Posted: 10/18/2016 6:22:16 PM EDT

[#13]

I run 147 gr Xtreme's under 4.5 gr WSF (~1000 FPS) out of a 4.5" MPX barrel chopped down from a 16".

I had issues at first with last round bolt hold open about 75% of the time. The gun cycled without issue it just wouldn't lock back. Turns out the gas ports on the original 16" barrels are a bit smaller. I reamed the gas port to 0.0625" and that seems to have fixed it.

If I ran it suppressed there were zero issues though, even before opening the gas port.

If you still have issues, I'd look into measuring the gas port and opening it up if it's less than .0600.

Posted: 10/18/2016 11:55:59 PM EDT

[#14]

Quote History

Quoted:
I run 147 gr Xtreme's under 4.5 gr WSF (~1000 FPS) out of a 4.5" MPX barrel chopped down from a 16".

I had issues at first with last round bolt hold open about 75% of the time. The gun cycled without issue it just wouldn't lock back. Turns out the gas ports on the original 16" barrels are a bit smaller. I reamed the gas port to 0.0625" and that seems to have fixed it.

If I ran it suppressed there were zero issues though, even before opening the gas port.

If you still have issues, I'd look into measuring the gas port and opening it up if it's less than .0600.

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I'm having the bolt not locking back issue too. I chronographed my loads today and they stick right around 1000. I'll look into the gas port thing, thanks.

Posted: 10/18/2016 11:56:57 PM EDT

[#15]

Quote History

Quoted:

If you never taken it apart, it may just have been lacking in proper lubrication from factory.
I always take my guns apart when I first get them (any part that is expected to be cleaned periodically) and clean/lube to make sure it start its break-in well lubed, and to fully understand what it will take to break them down, should it ever be needed in the field.

View Quote View All Quotes

View All Quotes

Quote History

Quoted:

Quoted:
Have you cleaned you piston assembly? Maybe its getting fouled up to much?

I read your post and decided it was time to give that a try, I hadn't taken it apart yet because I figured if it was working with supers then subs shouldn't be a problem either, but I guess I dont have any science to merit that. So I took it apart and it was a bit tough to get apart and it was definitely dry in there. Nothing too heavy as far as residue, but I cleaned it out and sprayed it with CLP and went back together.

First round immediately stove piped, cleared it and fired 14 rounds perfectly. I'll fire the rest of the batch I have loaded and go from there. I didn't think after a few hundred rounds it would be enough to make the gas system useless, that seems to be it though.

If you never taken it apart, it may just have been lacking in proper lubrication from factory.
I always take my guns apart when I first get them (any part that is expected to be cleaned periodically) and clean/lube to make sure it start its break-in well lubed, and to fully understand what it will take to break them down, should it ever be needed in the field.

You're right, and I totally neglected it. Small price to pay, but it still appears to be working.

[ARCHIVED THREAD] - Can't get my mpx to cycle subs.

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