I’ve seen this issue accross the internet and seems to be random, some guns work, some don’t. While my gen 2 mpx has been 100 percent reliable, I can’t seem to get it to group better than 6-8 inches at 25 yards. My mp5 and mp5k clones all shoot clover leaves / 1 inch groups, but the mix with both the factory barrel as well as an ILWT barrel all shoot wonky. I tried chopping the factory down and shot it both with the trilug and direct thread suppressed with the same results.

Also the mpx will sometimes group okay and then throw a random round way to the left or the right. This is both suppressed and unsuppressed and have shot 9mm and .45 cans on it. No evidence of a baffle strike or anything.  

Just wondering if anyone has had success getting a lemon to shoot better or if I should just keep this sucker in the back of the safe.

Only thing I can think to do is take apart, clean, put back together and make sure it’s all torqued to spec, and maybe mess with stronger springs from ILWT.

Mp5 with omega 9k trilug at 25 with 147 G2

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Mpx at 25 with 147 G2 and 124 NATO

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Thanks!

Something clearly isn't right with your MPX...Mine is a tack driver with the ILWT tri lug barrel. Either your barrel is loose or your optic is loose? Are you using a red dot? if sso Take it off and try a different one and mount...if using Irons check the sights for looseness

Thanks dude, yeah optic is tight and witness marked. Barrel was torqued tight. Going to take it back out after checking everything and report back. Love the platform and would really love it if it performs. Thanks!

I like the MPX, but got rid of it and now have the B&T APC9k, which is 100% reliable all the time and highly accurate.

I’ve got one of the newer MPX K’s and it shoots 5-6” groups at 25 yards with a red dot.I have gotten better groups out of it with certain ammo but by the time I realized the inconsistencies were ammo related I moved on to other guns.At some point I’m gonna revisit it and work up a load.

Torqued tight or torqued to spec?

I have the same accuracy "complaints" with my MPX-k. I'm running the factory barrel with the ILWT 3-lug adapter. Both the barrel and the adapter have been removed and re-installed and torqued to spec multiple times. I'm not ready to swap the barrel for an ILWT barrel, but my next plan is to remove the 3-lug adapter and direct thread a suppressor with a 13.5x1LH taper adaptor.

I put a couple of videos on YouTube regarding this topic, here are a couple of screen shots when compared to my PTR9.

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Did it shoot like that straight from the factory without changing anything?  Factory barrel, flash hider, etc

Have you tried putting a different optic on it?  Maybe the dot is shifting shot-to-shot. What optic are you using

I agree. try a different optic...you dont have to "zero" the new optic...as long as it is on paper you just want to see how the grouping is

I've pretty much given up on my MPX K.  I've spent a stupid amount of money trying to get it to shoot reasonably well.  ILWT barrel, adjustable gas plug, different rate springs, different trip-lug adaptors (including the ILWT MPX specific one) on the factory barrel.  Even with my CGS MOD 9 direct thread mounted, the best groups are 4"+ at 25 yards.  My Zenith MP5 clone, and APC9 shoot clover leafs at that range.

I may throw a Hail Mary pass, and pick up a longer barrel, since the accuracy issues seem more prevalent on the 4.5" guns.  That kind of defeats the purpose of the "K" though.

I SBR'd it before I had my 9mm can and discovered all the issues.  It would have been out the door and long gone years ago if it wasn't an SBR.

Wow.  We are twins.  I've SBR'd mine before finding the same issues.  I have tried different tri lug adapters, direct thread, ILWT barrel with adjustable gas.  I shot mine again today with and without a suppressor after cleaning both the weapon and suppressor.  4" at 25 yards is where I'm at regardless of subsonic or supersonic ammo.  Mine is also the 4.5" model.  I've got just over 2,000 rounds through mine, and while fun to shoot isn't a very accurate firearm.

I’m dealing with a recently purchased, previously owned MPX Copperhead.

With the factory 3” barrel I can get tiny groups, but the reason I bought the gun was that it came with a ILWT 4 1/2” barrel that I could mount a suppressor on.

I’m getting 4-6” groups with the ILWT barrel, and significant trigger slap.

After communicating with the owner of ILWT I’m waiting on a couple of different gas plugs and extra power springs.

If it’s only accurate with the hog nose barrel I’ll probably pass it on at a loss.

Update:
I went with smallest gas plug.
.049 torqued the barrel to spec.
Changed out the older Sig Romeo 5 that came with the gun for a newer one that I had.
The gun works fine, trigger slap is gone, and I got some 2” groups (when I did my part).

I’m relieved.
I was afraid the gun would only shoot decent groups with short barrel.

I didn’t shoot a lot of rounds with my YHM R9, but POI is still off by a couple of feet when it’s attached.
Suppressed groups seemed to be about 2” bigger.
I’ve thought about using Magpul folding sights and have them zeroed for the suppressor and zero the Romeo for non suppressed shooting.

I echo this, it's acceptable with direct thread. I'm debating removing it from the registry and dumping it. Then I would be Sig free.
Although I haven't tried the smaller gas plug. The gun does work though, never malfunctioned.

Such a "neat" little gun.  But my Benelli M4 with buckshot shoots better groups.

So are ILWT barrels not accurate?

Mine is a sample size of 1, so take that for what its worth.

The ILWT barrel on my gun, using the tri lug and Lawman 147gr ammo is around 4" or so at 25, with my MOD9 suppressor.  Without the suppressor, it's slightly better.

The factory barrel, with an ILWT MPX specific tri lug adaptor was 6"+ at 25 using the same ammo.  With the can direct threaded on the factory barrel, probably closer to 4".

I'm waiting for the form 3 to clear on a Wolfman, once it gets out of jail I'll give it a go on the MPX.

Anyone have issues with the 8” as well?  I have a relatively newly acquired gen3 8” LE.  As soon as I get the rad45 in hand (any day now), I’ll be using the ILWT tapered tri-lug and the HUXWRX 3 lug mount.  I’ll do some testing in the factory setting, without a MD, with the ilwt 3-lug, and finally with the suppressor.

My dude, watched all your vids. Your gun basically shoots the same as mine tossing random rounds and opening up the groups. And I’ve tried multiple optics, direct thread and trilug, etc, different bullets from range to defense loads from 115 to 147 grain. Bummed to hear so many folks have issues with this platform and wonder why it’s not more resilient from an engineering standpoint.

Love the way it handles and shoots but wish it was more accurate. Still need to get to the range and try it in my last ditch configuration to see if it works.

And for the other folks still in the thread, never really shot great, which is why I went with the ILWT barrel. I have the adjustable gas plug barrel and will group it with all the gas settings and a trilug griffin 45 can and then shoot it direct thread and see what happens.

Anyone make a direct thread hub 13.5x1LH tapered adapter? I have yet to find one...

Do you mean an adapter to use a different thread pitch?

I've been looking, and I haven't found one.

I'm looking for a tapered 13.5x1 LH direct thread suppressor HUB adapter (or one for an Obsidian 9/Omega 9k). I'm trying to remove as many variables and adapters as I can, so not interested in a 1/2x28 conversion adapter. I may pick up the Griffin 13.5x1 LH taper 3-lug to see if it provides any better accuracy than the ILWT 3-lug adapter I have.

+1 can't get accuracy for crap. I was trying to shoot steel at 25 and 50 yards. Im more accurate with a handgun.

I'm running a ilwt barrel as well. I gave up on trilug.

Now I'm using plan a, bit i haven't shot for accuracy. It's just depressing.

Already form 1'd. Whatever. At least it looks cool.

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My Gen 1 8" shoots great unsuppressed, but as soon as I put a suppressor on it shoots 7"+ groups at 25 yards. I've tried tri-lug and direct thread. Sad to hear that even an aftermarket barrel won't fix it.

Played around with (3) cans now both with them attached via tri lug and also with direct thread.  Same results whether with factory Sig 4.5" barrel or ILWT 4.5" barrel.  Tried two different quality optics and quality mounts as well.  Pretty sad I can shoot the same groups with a red dot handgun (MPX has been form 1'd and using a stock and bags at 15 yards with unacceptable groups).

Alright dudes. Took the mpx back out today after tearing it down and retorquing the barrel screws to 40 inch pounds. Using the ILWT 4.5 inch barrel with adj gas plug, dialed down to the min gas setting, and using a griffin revolution 45 can on the tri lug mount. Got a 3-4 inch group at 25 and kept most of them in the 9 ring on a birchwood B8ish at 50 yards. For how much I’ve messed with this, I’ll take it as a win. My basderd coharie mp5 clone shoots groups a quarter the size, but at least the mpx isn’t throwing random rounds all over and keeping them somewhat centered.

This was all speed gold dot g2 147 grain.

At least it’s been 100 percent reliable. Going to just wipe it down and lube it up and leave it. I feel like if I look at it funny it will act up again.

1st group at 25. 10 shots

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2nd group at 50. 10 shots

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That is practically what my APC9k got …

Tried Ecco Machine?

@thehun06

I just got a taper shoulder adapter and running in direct thread 13.5LH …

Suppressor stamp came in, so I did a little testing.  First group was before I had the suppressor.

8” gen3 unsuppressed in factory setting (A2 FH), 25y, federal AE 147’s



ILWT 3-lug, Rad45 suppressor (full length config), 25y. This was the only group this day.  Once I saw it would group well, I just got to blasting.  I’ll shoot more groups consecutively next time.





Overall, seems like acceptable groups with a red dot.

Well, here's hoping this fixes the accuracy issue with my MPX.

My B&T MP5SDK suppressor is still in jail, and the 8" hand guard is out getting ceraKote to match the gun.

I wonder why it is so sensitive to a suppressor.


Generally, a can won't cause accuracy issues unless there is a baffle strike, which there doesn't seem to be.  Gas turbulence is a thing...but pistol bullets are not generating 50K PSI and aren't boat tail bullets, so it shouldn't really be a thing.  Alternatively, a can could wobble on a 3 lug...maybe.  It could cause issues if it induced barrel flex due to a light barrel or inadequate barrel thickness in the threaded area.  Over torqued muzzle devices can damage a barrel...but unlikely.  Something could be contacting something...like can touching rail or similar...but obvious and unlikely.  Back pressure could affect cyclic rate which could cause it to unlock prematurely...but thats generally rare as the bullet is usually gone before the unlocking occurs.  

Odd.

Ecco machine makes an "alpha" 13.5x1lh mount that shoulders on the muzzle(like all 13.5mm mounts should).  It's aluminum and I believe under $50.......
I don't have an omega 9k but I'm 99.9% sure it uses a normal "alpha" mount, right?  

https://www.eccomachine.net/product/1-125-28-alpha-ultralight-aluminum-direct-thread-mounts/

I have an early gen2 factory SBR with the 8 inch barrel and an extra sig barrel that was shortened to about 4 inches and both shoot fine.  
Never shot groups, but with a cheap red dot it's no problem to hit a paper plate size target at 100 yards from a bench.  Standing and unsupported is maybe 50% hits.

I threw my "Hail Mary" pass for accuracy on my MPX.  My "K" is now an "SD".  B&T "K" can, on an ILWT SD barrel.  Hopefully this fixes the accuracy issues.  That's an MI 8" hand guard.  If I was going to do it over again, I'd go with the Ronin arms conversion, as it's a couple of inches shorter.

Looks good.  Now go shoot some groups

Rob from ILWT has mentioned that it is likely an issue with overgassing, causing bolt to unlock early. Tracks with how cans seem to make groups open, and how gassy the MPX is with a can.  Haven't taken it out yet in a while, but my mpx with 4.5" ILWT barrel and restricted gas plug, 20% extra power springs, and wolfman in k config gets like 2"ish groups iirc.

I haven’t noticed my mpx to be gassy.  I’ve only ever shot it suppressed with the rad45 though, so maybe pushing the gas out the front has a positive effect on groups.  Mine shoots great.

I have a ilwt 3-lug adapter with the Huxwrx mount.  There’s a little more wiggle than I care for, so I’m trying the 3-lug MD & mount from silencerco.  Supposed to be a tighter lock-up.  Should have it by today

I pulled the ILWT 3-lug adapter off and replaced it with a Rearden mount (13.5x1 LH tapered). I also ordered the low profile adapter for the Omega 9k that's currently in jail. We'll see if this can tighten up my groups suppressed, but I'm kind of digging this look. Interestingly, when I pulled off the ILWT 3-lug adapter it felt like it was binding, and sure enough, I appeared to have stripped out threads on the inside of the mount. Muzzle threads appear perfect and the Rearden mount went on smooth.

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Results are in with the Rearden setup. This is much more what I was expecting to get out of the MPX. My advise at this time is to ditch the ILWT 3-Lug adapter. I want to try the Griffin adapter, but I'm satisfied with these results and I'm tired of messing with it.

These are all from 25 yards
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what's the overall length on that ?

Eek! I was planning on replacing my CMMG Banshee with an MPX for competition shooting.
This thread is concerning.

I actually said screw it and re-threaded my OEM 8" barrel to 1/2-28 ... had to lose about .75" so it is now a 7.25" barrel ... but the 13.5LH is very stupid on Sigs part ...

I took my 8" MPX out to shoot groups and verify zero. I haven't been shooting it much lately, as I have been shooting my MP5K-PDW clone much more often. I decided to do a side by side comparison and I found my MPX was better in just about every test I could come up with. My MPX was more accurate than my MP5, though it's still a 9mm. I won't claim it's comparable to an AR or anything, but shooting the 8x8" plate I set up from 100 yards was easy at a rapid pace. On paper the groups were tighter with the MPX. Split times were faster for me. The MPX deviated less when attaching the suppressor, though they both deviated a considerable amount. MPX was a bit more gassy while suppressed, and the MP5K is obviously easier to conceal. I keep the MP5K in a leather laptop bag. Shooting 147 grain while suppressed the MPX felt quieter to my ear, but that doesn't really mean anything.

I'm going to keep the MPX unsuppressed for the foreseeable future. Also, shooting stuff is fun.

Took my mp5k out the other day and had some crazy groups with an AAC Tirant 9 on a three lug mount, that actually shot great on a different range trip, threw my omega 9k on it using a 3 lug and groups tightened right back up. Bizarre to me so I’ll take it out again in a couple of weeks.

I love the way my chopped mpx shots suppressed with the ILWT gas plug, just wish it was a tad more accurate. Will put them all head to head (mp5, mp5k, and mpx) again soon and post the results here with a few different loads.

I'd pile onto this and say that I've had 3 barrels for two MPX's (6.5" and 8" SIG and 16" ILWT) and none of them have been impressive accuracy wise.  However fighting with them I have learned some things.  Most of the B&T and CZ Scorpions I've seen/shot were significantly better accuracy wise, as has been pretty much every AR 9mm platform I've seen.  Especially suppressed, for some reason suppressing the MPX seems to degrade accuracy more than on any other platform I've seen.

1) the twist rate wants heavy bullets, not 115-124gr range ammo and it seems to like hotter loads.  For example the Win Nato 124gr early on in testing 115/124gr rounds was an early stand out, but still not impressive 5-6" groups at 50yds off a rest. I think much more than most 9mm's you really have to hand load for these if you want any kind of accuracy.

2) The MPX is just a picky machine, it's one of those guns you really have to find a load/setting that it likes and be happy with it and run it.   I've tried everything from heavier recoil springs, to adjustable gas plugs, short of handloading a heavy 9mm round nothing seems to make lighter factory ammo shoot well out of most of them.   If all you want to do is hit a 8" plate at 25yds, that's fine, but at that point why even use an MPX, plenty of 9mm handguns will do that all day and have 20+ round capacities, optics, etc. now.  At that point what does the MPX even bring to the table that a handgun doesn't for 1/3 of the cost, size, and weight.

3) Sig basically knows about as much as a 5th grader does about how to make a semi-auto gun work reliably......almost every new design they've released 320, 365, MCX, MPX, P210 US etc. have suffered from slide/bolt speed or recoil spring related issues etc.  The MPX has such a violent bolt speed, the only way Giessele could make a trigger stay together for it was to force the user into using +45-60% recoil springs to try and slow it down.

Heavier loads worked better because of the twist rate of the barrel, but many commonly available heavy factory loads in 9mm these days are very weakly charged and the MPX won't run them.   One of the first "heavy" 9mm loads I tried was some of the Federal Synatc in 130/150gr versions and neither would run in my MPX.  The downside of course is if it's just a range toy, 147gr FMJ ammo is 2x the cost of 115gr.

We used to do a lot of testing of pistols in ransom rests as bored range folks, usually when someone would be at a loss that their gun just won't shoot or the sights would be "way off".  Just about any $600-700 factory combat handgun with fed/win 115gr range ammo would shoot 2-3" groups at 25yds and 5" groups at 50.  That's an entire handgun that costs less than JUST the MPX barrel from Sig, and yet they still struggle to deliver similar accuracy.   4" at 25yds is a joke.  Bullseye 9mm handguns are shooting 1-1.5" groups at 50yds.   This is nothing new for Sig though, the MCX as well has filled forums for years with reports of poor accuracy, if I remember right Sig's standard is 4" at 100 yards for the MCX, so clearly they are not concerned with accuracy.  It's not a precision rifle, but tons of AR's will hold 2 MOA easily with descent ammo, an MPX should easily hold 2-3" at 25 yds and 4-5" at 50yds with descent factory range ammo.