JP Enterprises Fmos bcg issues

Lexyallen2

Lexyallen2

Private
Minuteman
Apr 12, 2023
19
8
Hawaii
solidbuilthomes.com
#1
Hello,

I have 2 LR .308's I built with Aero Precision lowers and uppers.
The 18" has a custom Bartlein barrel and the 16" has a Wilson combat Recon barrel.

No matter what the configuration, the JP bcg ALWAYS jams.

Conversely, Whenever I use my Aero Precision bcg, no matter what the spring/ weight configuration, it runs flawlessly.
- both rifles run FLAWLESSLY with the Aero Precision bcg in any spring/ gas/ buffer/ magazine/ ammo configuration.

For example, if I put a regular buffer spring with a 3.4 oz buffer weight in both rifles, both rifles run flawlessly with the Aero Precision bolt... however, both rifles will jam with the JP enterprises fmos bcg (empty casing above new round that won't feed).

If I put Springco Orange buffer spring in both rifles with 5.1 buffer weight, again, the Aero Precision bcg runs flawlessly, but when I put the JP enterprises fmos bcg in, they both fail to cycle.
It's not a gas issue.
It's not a barrel or custom build issue.
If it were, then the rifles wouldn't feed perfectly with the Aero Precision bcg.

I always test each set up on each rifle with the same springs/ ammo/ mags etc to isolate the bcg variable- so, the only variable in each comparison is the bcg: Aero Precision bcg vs the JP Enterprises bcg_ (high pressure bolt)... everything else is the same.... the JP enterprises fmos bcg always fails to cycle... the Aero Precision bcg always produces 100% reliable feeds..
Something must be wrong with the JP enterprises fmos bcg/ high pressure bolt.
I've emailed JP Enterprises twice.... haven't heard back yet... I've wasted thousands chasing this issue thinking it must've been something I did wrong with my build... but, apparently, that's not the case.
What do yall think?
 

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#4
You should just call JP. They will answer the phone. I use the JP FMOS on a 20” 260 gasser along with their SCS system. Runs flawless. It probably is a gas issue. The FMOS is heavy. You probably aren’t getting enough gas for it to fully cycle which is why it isn’t ejecting and picking up the next round.

What length is your gas system? What’s the gas port size? What gas block are you currently using?
 
#5
TonyTheTiger said:
Swap the one piece gas ring on the JP bolt for standard rings and see what happens.
Click to expand...
Ok... thats the one variable I didn't consider... however, an interesting side note- when I tested with a light spring and a light 3.4 oz buffer weight, I would get light primer strikes with the JP bcg.... I think the extractor/ ejector is too tight... those light primer strikes were weird... so, I put the Aero bcg in with the light spring and buffer weight, and, again, it cycled outstanding.
When I put a heavier spring and weight in, the light primer strike issued disappeared... but, still couldn't get it to cycle..
But, that light primer issue in conjunction with the failure to feed makes me think something is up with ejector/ extractor
 
#6
_Windrider_ said:
You should just call JP. They will answer the phone. I use the JP FMOS on a 20” 260 gasser along with their SCS system. Runs flawless. It probably is a gas issue. The FMOS is heavy. You probably aren’t getting enough gas for it to fully cycle which is why it isn’t ejecting and picking up the next round.

What length is your gas system? What’s the gas port size? What gas block are you currently using?
Click to expand...
If it were a gas problem, then my Aero Precision bcg wouldn't work either..
I've got a Superlative arms adjustable gas block... I've tried it both on restrictive and with bleedoff AND tried extra adjusting to give it more gas...
But, again, if the Aero Precision bcg works with the gas setup, and not the JP, then the problem is the JP enterprises fmos bcg.... it won't cycle with the JP, but it cycles with the Aero... that pretty much cancels out a potential gas problem issue.
 
#7
_Windrider_ said:
You should just call JP. They will answer the phone. I use the JP FMOS on a 20” 260 gasser along with their SCS system. Runs flawless. It probably is a gas issue. The FMOS is heavy. You probably aren’t getting enough gas for it to fully cycle which is why it isn’t ejecting and picking up the next round.

What length is your gas system? What’s the gas port size? What gas block are you currently using?
Click to expand...
Also, the Aero bcg weighs 18oz and the JP weighs 18.4oz... so, that small difference in weight shouldn't matter considering all the different gas/ spring and weight variables I tested... not only that, but, every time I upped the buffer or spring rate, I adjusted the gas accordingly... I put one round in until the bolt holds back after a shot, then I add 1 more click higher for extra gas for added reliability... and, I start with 145 gr ammo for setting the gas, and then move up in ammo power...
I'm in Hawaii, so I have to remember to call jp in the morning, otherwise, every time I think about it in the afternoon (my time) they're already closed
 

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#8
Lexyallen2 said:
Also, the Aero bcg weighs 18oz and the JP weighs 18.4oz... so, that small difference in weight shouldn't matter considering all the different gas/ spring and weight variables I tested... not only that, but, every time I upped the buffer or spring rate, I adjusted the gas accordingly... I put one round in until the bolt holds back after a shot, then I add 1 more click higher for extra gas for added reliability... and, I start with 145 gr ammo for setting the gas, and then move up in ammo power...
I'm in Hawaii, so I have to remember to call jp in the morning, otherwise, every time I think about it in the afternoon (my time) they're already closed
Click to expand...
Just throwing it out there. Good luck. Hopefully JP has some insight for you. Where in Hawaii? I lived in millilani, lahaina and kona for a few years
 
#12
one interesting discovery- when I used the JP enterprises bcg with a light spring and light buffer weight, I'd get light primer strikes... that was weird. As soon as I increased the buffer weight, the light primer strikes went away.. its like the JP bcg needed more force/ weight/ momentum to seat the round..
That's why I think the extractor/ ejector are too tight.... with a light buffer set up, I get light primer strikes, and with a heavier buffer setup, I get failure to feed (empty casing on top of a round trying to go in... exact same jam every time) but no light primer strikes....

It's like the ejector is so tight, it's releasing the casing too soon; and with the lighter buffer set up, there's not enough power to fully seat the round..
 
#13
Lexyallen2 said:
one interesting discovery- when I used the JP enterprises bcg with a light spring and light buffer weight, I'd get light primer strikes... that was weird. As soon as I increased the buffer weight, the light primer strikes went away.. its like the JP bcg needed more force/ weight/ momentum to seat the round..
That's why I think the extractor/ ejector are too tight.... with a light buffer set up, I get light primer strikes, and with a heavier buffer setup, I get failure to feed (empty casing on top of a round trying to go in... exact same jam every time) but no light primer strikes....

It's like the ejector is so tight, it's releasing the casing too soon; and with the lighter buffer set up, there's not enough power to fully seat the round..
Click to expand...

What bolt are those barrels headspace to??? If any?

And while running the JP BCG with thier single gas ring there is actually less friction..
 
#17
Lexyallen2 said:
I'm not sure how I would check that- the screws are staked, and it seems solid.
But, good news- JP just emailed me and said they'll check it out and make the necessary corrections
Click to expand...

Just curious, is it failing to chamber or extract?? And this is with box ammo? And making a judgment by trying to chamber a empty fired case isn't a reliable way to test, my FF cases don't like to chamber either especially if you've got a fair bit of carbon in your chamber...I know you've mentioned some of this but just looking for clarification...

One more thing, after you decide on your buffing weight/system... adjusting your gas to lock the BCG back and adding one click isn't always reliable... once you pick your ammo or load that's a good place to start but it's more reliable for perfect fuctioning to adjust your gas by the ejection pattern.. you want those cases ejecting between 3-3:45 o'clock that seems to be the sweet spot...
 
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#19
The BCG is part of the gas system. It may be properly gassed at the block but may not be at the BCG. I'm more inclined to focus on extraction. Does the bolt lock back on an empty mag when fired with one round? Despite being JPE, I'd strip the bolt, and replace all of the springs and gas rings with Sprinco replacement parts. Can you swap the carriers and get it to run with the Aero bolt and JP carrier?
 
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#20
bigjake83 said:
Just curious, is it failing to chamber or extract?? And this is with box ammo? And making a judgment by trying to chamber a empty fired case isn't a reliable way to test, my FF cases don't like to chamber either especially if you've got a fair bit of carbon in your chamber.
Click to expand...
Its failing to extract- the spent casing stays in the upper, and the next round jams against it while trying to chamber...
Yes, regular box ammo.
I haven't chambered an empty case.
 
#21
Cascade Hemi said:
The BCG is part of the gas system. It may be properly gassed at the block but may not be at the BCG. I'm more inclined to focus on extraction. Does the bolt lock back on an empty mag when fired with one round? Despite being JPE, I'd strip the bolt, and replace all of the springs and gas rings with Sprinco replacement parts. Can you swap the carriers and get it to run with the Aero bolt and JP carrier?
Click to expand...
Hi, yes, the bolt locks back on an empty mag...I'm sending the bcg back to JP for inspection. I do think, however, the extractor and ejector are too tight.
 
#24
jb0311 said:
True, but I was more referring to their CS. Good folks.
Click to expand...
Yep, they emailed me back this morning... they didn't respond to my first email a couple of weeks ago, and, initially, I was put off by that... but, apparently, that initial email got overlooked.... no worries, their response this morning shows good faith and concern, so, I'm thankful.... These other companies have also shown impeccable customer service in the past: Kidd Innovative Design, Brownells, Vortex, and Craddock Precision.
 
#26
Lexyallen2 said:
Yep, they emailed me back this morning... they didn't respond to my first email a couple of weeks ago, and, initially, I was put off by that... but, apparently, that initial email got overlooked.... no worries, their response this morning shows good faith and concern, so, I'm thankful.... These other companies have also shown impeccable customer service in the past: Kidd Innovative Design, Brownells, Vortex, and Craddock Precision.
Click to expand...
Paul Craddock is a legend. Man chambers a nasty AR barrel. Only guy I trust for those.
 
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