:-) MPX :-)

[eastern_hunter]

Son just brought home an MPX. We popped of the forearm and removed the flash hider. Thread is 13.5x1 LH. Mounted an Octane 9HD with that piston and a spacer cage and hit the range in the long side yard!

Excellent suppression ... darned near Hollywood quiet with a 150 gr 1000 fps FMJ load I worked out for pistols! Very accurate too. Hitting the swinger inside the center of an AR500 steel target with ease at 30 yards ... bouncing it back and forth inside to out and back.

Cool piece Great with the Octane 9HD!

[hyrulejedi86]

We have to see a video of this! Would you be willing to share your handload? If it uses 150 gr bullets then perhaps it would work similarly with 147s.

[eastern_hunter]

Have never tried to make a video so not at all sure if I even have the stuff to do it.

Load info

1) 9x19 150 gr FMJ projectile; CCI 500 primers; 4.7 gr 3n37; OAL = 1.159"

Used the same load with 147 gr XTPs ... OAL = 1.120

I know it's an odd powder but have a bunch left from the IPSC days. Is very clean burning. Is between AA #5 and AA #7 in burn rate.

[DKDravis]

Used the same load with 147 gr XTPs ... OAL = 1.120

Dang ..
Thats Exactly the same load I used for my Glock, for long range fun stuff years ago ..

Vitahvuori 3N37 ... brilliant stuff ... I still use it a lot in 9mm target loads ..

[tripntx]

In June i purchased a MPX, ordered a Sig Collapsible stock for it, and mailed a Form 1 to SBR it. The Form 1 to SBR my MPX came back approved yesterday. Bad news the collapsible stock from Sig is still on back order.

[eastern_hunter]

Great little toy!

Son likes it better than the MP5 ... a lot better.

[bnanaphone]

Did you get any gas to the face when shooting suppressed? I have heard those guns are over-gassed with a can, which is what has kept me from diving in on one.

Thanks for the input.

[eastern_hunter]

A little blowback ... not much actually. Wish they had cut the charging handle as the newer BCMs are cut. That would have eliminated it completely.

Sighted it in today with 158 gr Fiocchi FMJ and an EoTech. Very nice indeed! Perhaps a little louder than my 3n37 handloads ... but not much. Rings steel nicely

[bnanaphone]

Thanks for the info.

There are a couple things with the MPX that have turned out to be different from what the original hype promised. I am not too keen on the proprietary charging handle and the inability to swap in AR15 triggers without voiding the warranty. I am glad yours is a good unit. Enjoy it.

[cpc989]

Thanks for the info.

There are a couple things with the MPX that have turned out to be different from what the original hype promised. I am not too keen on the proprietary charging handle and the inability to swap in AR15 triggers without voiding the warranty. I am glad yours is a good unit. Enjoy it.

Wow you cant swap triggers without voiding warranty? That's ridiculous.

[TROOPER]

Thanks for the info.

There are a couple things with the MPX that have turned out to be different from what the original hype promised. I am not too keen on the proprietary charging handle and the inability to swap in AR15 triggers without voiding the warranty. I am glad yours is a good unit. Enjoy it.

Wow you cant swap triggers without voiding warranty? That's ridiculous.

It's a "CYA" thing in case the new trigger bounce-fires, Sig doesn't want to be on-the-hook for taking part in creating a machine gun.

That said, many individuals on other forums have installed Gieselle or the like without issue.

[cpc989]

Thanks for the info.

There are a couple things with the MPX that have turned out to be different from what the original hype promised. I am not too keen on the proprietary charging handle and the inability to swap in AR15 triggers without voiding the warranty. I am glad yours is a good unit. Enjoy it.

Wow you cant swap triggers without voiding warranty? That's ridiculous.

It's a "CYA" thing in case the new trigger bounce-fires, Sig doesn't want to be on-the-hook for taking part in creating a machine gun.

That said, many individuals on other forums have installed Gieselle or the like without issue.

Makes sense I guess. I still want one but I think I want to wait for the gen 2 with new hand guard and shorter barrel options to come out.

[TROOPER]

I had considered a shorter-barreled, shorter handgaurd model, but then I realized that the barrel length was irrelevant as long as they were using 13.5 LH threads. I wanted 1/2 x 28, and in order to get that, the barrel had to be cut and threaded. Plus, I do want the handgaurd to be longer, and just figured the silencer would sit under the handgaurd.



The barrel is the chamber + three inches. The silencer is an older AAC Evo-9, but I have a Thompson Machine SG-2 in silencer purgatory. As far as I have been able to tell, the TM SG-2 is the largest 9mm silencer on the market that will still fit under the MPX hand-guard. It's made for a sub-machine gun, and I'm counting on the extra volume and length to make up for the fact that it's using a monocore instead of k-baffles. While at the same time, I'm hoping to reduce the blow-back. Is the blow-back bad? No, not at all. But NO blow-back is welcome, and if I can reduce a little bit to an even smaller amount, then that's my goal.

Plus, it frees up the Evo-9 to go back to the GLOCK.

[hyrulejedi86]

That is a pretty awesome setup! I'm jealous of that! Has the MPX lost any accuracy from the barrel cutting and thread changing?

[TROOPER]

That is a pretty awesome setup! I'm jealous of that! Has the MPX lost any accuracy from the barrel cutting and thread changing?

I don't know. I had the barrel off getting cut and threaded while the SBR was working its way through the ATF. I never fired it with the 8-inch barrel it came with since I just didn't want to shoot it as a pistol.

How does it shoot now? Very well. But it isn't a bench or bipod gun, and I've only shot it standing "off hand". I myself seem to be the limiting factor. If I was a better shot I could give you a better report. The bottom line is that I'm not disappointed. If I had the chance to do it over, I'd probably tack on an inch just because, but I didn't word my cut-and-thread request very well, and I got what I ordered instead of what I wanted.

I'm not disappointed.

[bnanaphone]

That said, many individuals on other forums have installed Gieselle or the like without issue.

If that is the case, I am less put off. I had read that it was due to the high velocity of the bolt or something that could damage a trigger. I did some research after reading your comment and did see where Bill Geissele himself stood behind the use of his triggers in these guns. I am a huge fan of his triggers and if/when I pick up an MPX, it will have an SSA in it.

Thanks for the correction Trooper.

[corey4]

I had considered a shorter-barreled, shorter handgaurd model, but then I realized that the barrel length was irrelevant as long as they were using 13.5 LH threads. I wanted 1/2 x 28, and in order to get that, the barrel had to be cut and threaded. Plus, I do want the handgaurd to be longer, and just figured the silencer would sit under the handgaurd.



The barrel is the chamber + three inches. The silencer is an older AAC Evo-9, but I have a Thompson Machine SG-2 in silencer purgatory. As far as I have been able to tell, the TM SG-2 is the largest 9mm silencer on the market that will still fit under the MPX hand-guard. It's made for a sub-machine gun, and I'm counting on the extra volume and length to make up for the fact that it's using a monocore instead of k-baffles. While at the same time, I'm hoping to reduce the blow-back. Is the blow-back bad? No, not at all. But NO blow-back is welcome, and if I can reduce a little bit to an even smaller amount, then that's my goal.

Plus, it frees up the Evo-9 to go back to the GLOCK.

i have been reading a lot of threads about the MPX and blowback over the last few weeks. when i first got mine (8" barrel), i was very disappointed in the amount of blow back with my octane9HD, to the point i was trying to sell my MPX and/or trade it in for another toy. but when i was reading some of your other discussions (multiple times), it got me thinking. you had mentioned sometime, somewhere about larger can volume and how it might help. so i took my osprey45 out with it today. i received zero blowback. i switched back and forth with the octane9 and osprey45 burning thru 200 rounds of american eagle 147 and 50 rounds of american eagle 115. most test strings were 10-15 rounds to get a good baseline and make sure i was actually perceiving corretly what was going on. when i finally determined the osprey45 provided no blowback, i did 3 30 round mag dumps...no blowback. so i took my MPX off the market where i had it listed for sale.

MPX 8"
american eagle 147 and 115
octane9HD provided terrible blowback with both loads
osprey45 provided zero blowback with both loads
all shots were taken NTCH, or as best i could do without a stock. without a stock, the recoil kinda punches you in the nose lol

so, i am now wondering if the design of the osprey with the monocore allows more gas to be blown into the can, and not into the action. i am also wondering if being a 45 allows more gas to escape thru the bore with the larger baffle openings and bore opening.

maybe in the next few days i will take my YHM cobra9 out. it has a monocore and a large bore opening. it is actually quite load compared to my octane9 and osprey with the same load.

so would a longer barrel be more beneficial to burn up more gas? you had mentioned in one of your threads that a shorter barrel would be better.

thanks!

[TROOPER]

so, i am now wondering if the design of the osprey with the monocore allows more gas to be blown into the can, and not into the action. i am also wondering if being a 45 allows more gas to escape thru the bore with the larger baffle openings and bore opening.

Probably a combination of the two. If I had to pick one, I'd guess it's the baffle design contributing the greatest amount of blow-back reduction.

maybe in the next few days i will take my YHM cobra9 out. it has a monocore and a large bore opening. it is actually quite load compared to my octane9 and osprey with the same load.

so would a longer barrel be more beneficial to burn up more gas? you had mentioned in one of your threads that a shorter barrel would be better.

thanks!

I suspect that a longer barrel wouldn't matter too much if a person jams a very efficient K-Baffle stack on the end, especially one with a very small blast chamber.

Also, I have speculated that a shorter barrel could be the ticket... but only if it's paired with a certain type of silencer: a monocore that focuses on a very large initial blast chamber. But such a silencer would be comparatively loud unless it had other positive attributes... lot's of volume... lot's of length. To that end, I believe the Thompson Machine SG-2 is the correct choice, and as far as my measurements are supporting, it is also the largest commercial 9mm that can still fit under the handguard. My thinking is that by creating a very low pressure area just beyond the muzzle, that the high-pressure gases will flow to the area of lowest pressure. A voluminous blast chamber sounds like just the ticket, because the more that goes in there, the less comes out of the ejection port.

Of course, considering how close the piston is to the chamber, you're never going to eliminate blow-back.

You've done a huge service by discovering that a 45 silencer is a meaningful way of reducing blow-back on this platform. I'm going to share that information on a few other forums.

[corey4]

You've done a huge service by discovering that a 45 silencer is a meaningful way of reducing blow-back on this platform. I'm going to share that information on a few other forums.

i would love to test an octane45 and an osprey9 to see if i get the same results.

[corey4]

I suspect that a longer barrel wouldn't matter too much if a person jams a very efficient K-Baffle stack on the end, especially one with a very small blast chamber.

i don't understand. isn't the octane9 a k-baffle?

[TROOPER]

K-baffles do better at restricting gas flow than do monocores (typically). Monocores typically have more volume to help overcome this flaw. I believe K-baffle stacks tend to produce more back-pressure. It's that back-pressure that is exacerbating the blow-back.

That doesn't answer your question... but I don't know the answer to your question. I'm not suggesting that a k-baffle is the worst-thing ever for an MPX -- far from it -- I'm just looking to reduce back pressure where I can, and while a k-baffle often produces better absolute sound suppression, that very strength in holding in gases is what is making for increases in back-pressure.

[Doc4975]

Hey Trooper,
Pretty sweet MPX you have and I would like to do essentially the same setup as you. However I have the tirant 9. Any complaints with the barrel length at 3" or issues with cycling? Or would you cut it to 4" if you did it over. Also, not sure if this matters but I will be running the 3lug quick adapter on my tirant rather then the direct thread. I appreciate any bodies feedback or suggestions.

[tripntx]

Called SIG last Monday, they said I'd receive my collapsible stock NLT the week after Thanksgiving. It's tough having an approved SBR Form 1 on hand with no stock, LOL.

Suppressors:
I ordered an Osprey 45 from Capitol Armory for use with my 8" barrel (should be clearing soon) since I have no intentions of cutting my stock 8" barrel. BUT, I do plan to purchase a 4.5" or shorter barrel once they become available either from SIG or aftermarket.

The comment above about the TM SG-2 has me wanting looking into them.

[quiettime]

i don't understand. isn't the octane9 a k-baffle?

No it's not, more of an M-baffle

[BigWonton]

I finally received my Mystic 3-lug adapter and with some time off, I got to take out the MPX, EVO and a couple of other guns.



I compared the Mystic with an Octane 9 with a GA 3-lug adapter. Although the Mystic was slightly less gassy, neither really bothered me. My 9mm loads are 147 gr Montana Gold CMJs with 3.3 gr of Titegroup.

Neither could compare to my 300 BLK Ruger American Ranch with a Harvester shooting Lucky 13's Zombie13 123grn bullets and 4.0 gr of Trailboss.