MPX-K accuracy issues?

[ARCHIVED THREAD] - MPX-K accuracy issues?

Posted: 12/30/2018 7:26:35 PM EDT

So I have a factory 4.5" gen 2 in which I installed a ILWT 3 lug adapter and hit the range. I'm getting 3-4" spread at 25 yards with a MRO. Same accuracy with or without my rugged obsidian 9 attached.
My MP5 with a 9" barrel with the same can running a T2 will shoot one ragged hole at 25 yards.
Now the Facebook gurus said they are ptting one ragged hole with a MPXK also. So I'm not sure if this is just a barrel issue or of it is normal.
Anyone else care to chime in with the accuracy of their K with the 4.5" barrel? Not sure what may be the issue other than the barrel at this point.
Was shooting 115 g WWB and Federal.

Posted: 12/30/2018 7:34:38 PM EDT

[#1]

Check the barrel screws....mine came a little loose after several hundred rounds affecting accuracy.

Posted: 12/30/2018 8:41:56 PM EDT

[#2]

Mine absolutely hates 115 grain bullets and gets similar results. I started using 147 grain rounds and it started to be a tack driver, not sure if it is an actual issue or if the MPXK simply hates the lighter 115 grain rounds.

Posted: 12/30/2018 10:18:25 PM EDT

[#3]

Quote History

Quoted:
Mine absolutely hates 115 grain bullets and gets similar results. I started using 147 grain rounds and it started to be a tack driver, not sure if it is an actual issue or if the MPXK simply hates the lighter 115 grain rounds.

View Quote

I had the same experience.

Posted: 12/31/2018 11:55:28 AM EDT

[#4]

Keep in mind you're talking factory vs. 3rd party barrel. They may not like the same things. Have also heard of accuracy issues w. the ILWT shorty barrels, but I assume it's a matter of finding what ammo it likes. Most guys want to plunk the same ammo in for everything.

Also, I'm in the same FB group... 5% are useful, 95% apes who shoot a 100rd. WWB every few months and think they're Delta snipers.

Posted: 12/31/2018 12:07:21 PM EDT

[#5]

Quote History

Quoted:
Keep in mind you're talking factory vs. 3rd party barrel. They may not like the same things. Have also heard of accuracy issues w. the ILWT shorty barrels, but I assume it's a matter of finding what ammo it likes. Most guys want to plunk the same ammo in for everything.

Also, I'm in the same FB group... 5% are useful, 95% apes who shoot a 100rd. WWB every few months and think they're Delta snipers.

View Quote

Looks like he has the stock Sig barrel, just using a 3rd party trilug adapter.

Posted: 12/31/2018 2:56:17 PM EDT

[#6]

Well throw me into the 95% mouth-breather/non-reader category, jeez.

I would also try a different weight/brand and see if it tightens up. If not, contact Sig. They may or may not take care of you.

Posted: 12/31/2018 4:49:20 PM EDT

[#7]

Maybe check loose screws, sights then muzzle crown and rifling. WWB has at least 2 different loadings. The Q4172 (115 fmjhb) has always been very accurate, at least years ago when actually buying factory rounds. The 100 round wwb (used to be brass jacketed) not so much. The gen2 8 in factory barrel owned was very accurate with 115 fmjhb.

Posted: 1/5/2019 8:13:43 PM EDT

[#8]

I only have 115 WWB, 115 Federal, and 124 Speer Lawman. I didn't see any difference in any of them. I tried removing muzzle devices and shooting bare barrel and same results.
Barrel screws are tight. I also tried a complete other optic and mount combo. No change.
It seems like a lot of people don't even test for accuracy because I can't find a lot of results by searching. If some tells me they are shooting one ragged hole at 25 yards with a 4.5" barrel I want a video as proof.

Posted: 1/6/2019 1:07:06 PM EDT

[#9]

Buy a box of 147 grain and check with those.

As I stated above, I couldn't get my MPX to group with 115 or some 124 even with a TA31 on top to see wtf was going on.

The 147 grains were stacking on top of each other.

Posted: 1/8/2019 9:58:51 PM EDT

[#10]

Ya I'm going to have to try that.

Posted: 1/17/2019 4:04:01 AM EDT

[#11]

Gas plug. A .0469 will tighten those groups right up. Add a suppressor you need the larger one. .055.

You're welcome.

Posted: 1/19/2019 10:27:26 AM EDT

[#12]

Quote History

Quoted:
Gas plug. A .0469 will tighten those groups right up. Add a suppressor you need the larger one. .055.

You're welcome.

View Quote

This thing is going through the Gambit. I have 147g Speer Lawman ammo now and it's been worked over and getting new barrel to test also which will be .055. Yes I'm going to be running with and without a suppressor.
I'll try and test again next weekend.

Posted: 1/19/2019 6:59:52 PM EDT

[#13]

So you’re saying that a 4.5 inch barrel MPX doesn’t have the same accuracy as a 9 inch barrel MP5? Not sure that ever will, based on barrel length alone.

Posted: 1/20/2019 12:31:39 AM EDT

[#14]

Have you tried removing that muzzle device and see what you get? I have seen MDs of all kinds screwup a barrels accuracy especailly if they are torqued down. Its easy to test and then you will know you have knocked it off as a variable. But different barrels certainly can do better with different bullets or bullet weight vel combos.

Posted: 1/20/2019 5:13:43 PM EDT

[#15]

Quote History

Quoted:
Have you tried removing that muzzle device and see what you get? I have seen MDs of all kinds screwup a barrels accuracy especailly if they are torqued down. Its easy to test and then you will know you have knocked it off as a variable. But different barrels certainly can do better with different bullets or bullet weight vel combos.

View Quote

Yep. Tried everything. No MD, 3 lug adapter, factory a2 md, etc
Trigger was replaced and thinking a timing issue was the issue, pulled the Piston and turned it into a bolt gun. Same results.
Like I said I will try and do some more testing next weekend with 147g

Posted: 1/20/2019 5:38:04 PM EDT

[#16]

I'm having the same problem with mine. ILWT 4.5" barrel and I'm ok at 25 yards (I don't really test groups, but I'm on an 8" steel plate consistently). However, pushing out to 50 yards, I can't even keep shots on the 10" steel plate. I aim center of the plate, and get every other shot or so on steel somewhere, but the rest splash around the target. It's like a 15" pattern at 50 yards.

I have tried several different kinds of ammo, but I'll check out some 147gr ammo and my barrel screws after reading the suggestions in this thread.

Posted: 3/18/2019 10:58:38 PM EDT

[#17]

I have a 4" not 4.5" MPX and it shoots 147's very, very well.

Posted: 3/19/2019 5:32:27 PM EDT

[#18]

Quote History

Quoted:
So you’re saying that a 4.5 inch barrel MPX doesn’t have the same accuracy as a 9 inch barrel MP5? Not sure that ever will, based on barrel length alone.

View Quote

What does its barrel length have to do with its accuracy?

Posted: 3/26/2019 11:31:30 PM EDT

[#19]

Jackal,

Same issues here with my K running a stock Sig 4.5” barrel. 115 Critical defense shoots best. 147 Lawman opens up to ~2” plus at 50 yds and throws 2-3 fliers out at 4” in a 10 shot string.

I’m running an SRD9-MPX fixed thread on mine which makes things even worse from what I’ve tested. This past weekend I tried the following loads:

147 gold dot
147 HST
147 Vcrown
147 superVel

My MPX w SRD9 was throwing them all over the place at 50yds. By that I mean ~12” either side of an 8” plate. Two shooters, off a bench, different loadings.

115 Fiocchi 9AP hot stuff shoots like garbage.
115 Aguila ball runs ok, better without the can, but not great.

I will be checking torque on all of the screws and plan on playing with the baffle orientation to try 50/50, all the same, and alternating baffles to see what that does.

I’m curious about how the gas port sizing may be impacting things.

Posted: 9/1/2019 11:13:52 PM EDT

[#20]

Jackal, I have a 2018 MPX K and am running into the same issues. Shot lousy with or w/o tri lug. Not sure I shot it with birdcage originally. Sent it to SIG w/o md on it. The smith's repair note said he"Hand lapped (the) barrel". Shoots decent now (about 6MOA with Tula 115gr) as long as it has the factory birdcage. Weird i know. Adding my Griffin tri lug still gives me 20+ MOA. No MD yields about 16 MOA. (All Tula for apples to apples comparison). I'm stumped. I shot all this from bags, multiple 5rd groups at 25 yds using an MRO.
Saw similar improvement with Win 147gr HP with the sig birdcage. Maybe this means my crown is bad? Honestly I'm kinda stumped. I'd like to solve this before I buy a can though.

Posted: 9/13/2019 12:04:49 PM EDT

[#21]

Quote History

Quoted:
So you're saying that a 4.5 inch barrel MPX doesn't have the same accuracy as a 9 inch barrel MP5? Not sure that ever will, based on barrel length alone.

View Quote

Barrel length has nothing to do with accuracy.

[ARCHIVED THREAD] - MPX-K accuracy issues?

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