Suppressor Zero Shift Fix?

[nalesq]

Can anything be done to fix extreme zero shift due to mounting a suppressor?

I have a Gemtech GM9 that, when mounted via 3-lug to a Sig MPX, will, at 50 yards, group over a foot to the left compared to when the suppressor is not mounted. (Curiously, at 25 yards, the leftward shift is only about 2-3 inches or so.)

By comparison, when the same suppressor is mounted via 3-lug to a Colt 9mm carbine, there is almost no discernible shift at 50 yards.

Any ideas on the cause, and how I might fix such an extreme shift on the MPX?


Sent from my iPhone using Tapatalk Pro

[HCM]

Can anything be done to fix extreme zero shift due to mounting a suppressor?

I have a Gemtech GM9 that, when mounted via 3-lug to a Sig MPX, will, at 50 yards, group over a foot to the left compared to when the suppressor is not mounted. (Curiously, at 25 yards, the leftward shift is only about 2-3 inches or so.)

By comparison, when the same suppressor is mounted via 3-lug to a Colt 9mm carbine, there is almost no discernible shift at 50 yards.

Any ideas on the cause, and how I might fix such an extreme shift on the MPX?


Sent from my iPhone using Tapatalk Pro

It’s not the suppressor. It’s either a defective barrel because the threads are not concentric or it’s the tapered shoulder on the MPX barrel.

Are you using an adaptor to square the shoulder and mount the 3 lug ? SIG used to sell these but stopped and won’t say why.

Options are:

send it back to SIG

Buy an aftermarket barrel

Buy a SIG or Q suppressor with a matching taper

MAC had a similar experience here:


https://youtu.be/Hm4npy5Dx3k

[nalesq]

It’s not the suppressor. It’s either a defective barrel because the threads are not concentric or it’s the tapered shoulder on the MPX barrel.

Are you using an adaptor to square the shoulder and mount the 3 lug ? SIG used to sell these but stopped and won’t say why.

Options are:

send it back to SIG

Buy an aftermarket barrel

Buy a SIG or Q suppressor with a matching taper

MAC had a similar experience here:


https://youtu.be/Hm4npy5Dx3k

Thanks for your insights! I do remember being surprised at the tapered barrel when I removed the original flash suppressor, and wondering if it would cause any issues with interfacing the 3 lug muzzle device. I guess the answer is ‘yes!’

I wonder if using this 3 lug adapter supposedly specifically designed to interface with the tapered barrel might also fix the issue?:

https://inleadwetrust.com/product/hk-style-3-lug-suppressor-adapter/



Sent from my iPhone using Tapatalk Pro

[HCM]

Thanks for your insights! I do remember being surprised at the tapered barrel when I removed the original flash suppressor, and wondering if it would cause any issues with interfacing the 3 lug muzzle device. I guess the answer is ‘yes!’

I wonder if using this 3 lug adapter supposedly specifically designed to interface with the tapered barrel might also fix the issue?:

https://inleadwetrust.com/product/hk-style-3-lug-suppressor-adapter/



Sent from my iPhone using Tapatalk Pro

Maybe, if the issue is the taper. However it’s more likely it is a defective barrel with non concentric threads.

[nalesq]

Maybe, if the issue is the taper. However it’s more likely it is a defective barrel with non concentric threads.

Besides the extreme zero shift, is there any other way to tell whether the threads are truly concentric or not?



Sent from my iPhone using Tapatalk Pro

[Default.mp3]

Besides the extreme zero shift, is there any other way to tell whether the threads are truly concentric or not?There are alignment rods out there you can use to check for concentricity once the can is mounted, though some of them aren't cheap (e.g., https://www.brownells.com/gunsmith-tools-supplies/rifle-tools/barrel-tools/bore-alignment-rod-prod104864.aspx). You might be able to tell with just a visual inspection. Might.

[Sensei]

Maybe, if the issue is the taper. However it’s more likely it is a defective barrel with non concentric threads.

Yep. It sounds like Sig had a bad batch of barrels with non-concentric threads. Good luck getting them to admit it.

[omega9]

There are alignment rods out there you can use to check for concentricity once the can is mounted, though some of them aren't cheap (e.g., https://www.brownells.com/gunsmith-tools-supplies/rifle-tools/barrel-tools/bore-alignment-rod-prod104864.aspx). You might be able to tell with just a visual inspection. Might.

This is a cheaper alternative that was posed over on M4C by JPMuscle. I haven’t picked up a can yet, so I haven’t tried them.

59973

https://www.mcmaster.com/8893K191-88645K33/

[Clusterfrack]

nalesq, that’s a pretty big shift. Are you getting baffle strikes? Key-holing?

[whomever]

This is a cheaper alternative that was posed over on M4C by JPMuscle. I haven’t picked up a can yet, so I haven’t tried them.

59973

https://www.mcmaster.com/8893K191-88645K33/

I've bought a fair amount of drill rod over the years. It isn't spec'd for straightness. In general, the stuff I've gotten won't be straight enough to use as an alignment rod.

Maybe shorter, fatter pieces for a pistol, but in general I don't think it will work well for rifles.

I have one of the .30 alignment rods, and I had the same idea, and tried several pieces of drill rod (and other stock) I had laying around as rods for a 22, and none were straight enough to be useful. You might get lucky, but don't count on it.

Any machinists in the house? It's fairly easy to grind long skinny stuff to an accurate diameter with a centerless grinder. I don't know how you grind it straight.

[nalesq]

nalesq, that’s a pretty big shift. Are you getting baffle strikes? Key-holing?

No visible baffle strikes and no keyholing.

I may get one of those rods next to see about the concentricity issue.



Sent from my iPhone using Tapatalk Pro

[nalesq]

As an update to this, I finally sent my MPX back to Sig describing my suppressor zero shift issue. They said the zero shift they discovered (4 inches at 25 yards) was “acceptable,” and “combat effective.” I reiterated that by 50 yards, the shift was more like 12 inches, and that moreover the group opened up significantly at that point as well. They opined, in essence, that 50 yards was beyond what they considered a “realistic” engagement distance for a 4.5-inch barreled 9mm weapon.

So there you have it. Don’t buy an MPX if being able to reliably hit a B8 at 50 yards with a suppressor mounted is particularly important to you.

It’s not super important to me, since this was to be my discreet backpack travel gun, and I probably wouldn’t bother packing a suppressor with it anyway. But I am still a bit disappointed.



Sent from my iPhone using Tapatalk Pro

[SeriousStudent]

I would be really effing pissed, not mildly disappointed.

I have a pair of suppressor alignment rods from Geissele just for this purpose. I got burned exactly this way on an AR barrel, and bought the 5.56 and 7.62 rods as insurance. I need to get a 9mm rod as well, I have a lot of 9mm quiet stuff.

Geissele puts the rods on sale periodically, and Brownell's does so as well. They are a worthwhile investment.

[Clusterfrack]

I don't have a significant zero shift in any of my suppressed 9mms at 25yds. I've only shot a few times at 50 yds, but I'm guessing something's weird with your can or mount.


As an update to this, I finally sent my MPX back to Sig describing my suppressor zero shift issue. They said the zero shift they discovered (4 inches at 25 yards) was “acceptable,” and “combat effective.” I reiterated that by 50 yards, the shift was more like 12 inches, and that moreover the group opened up significantly at that point as well. They opined, in essence, that 50 yards was beyond what they considered a “realistic” engagement distance for a 4.5-inch barreled 9mm weapon.

So there you have it. Don’t buy an MPX if being able to reliably hit a B8 at 50 yards with a suppressor mounted is particularly important to you.

It’s not super important to me, since this was to be my discreet backpack travel gun, and I probably wouldn’t bother packing a suppressor with it anyway. But I am still a bit disappointed.

[nalesq]

I don't have a significant zero shift in any of my suppressed 9mms at 25yds. I've only shot a few times at 50 yds, but I'm guessing something's weird with your can or mount.

Sig also more or less blamed the mount and suppressor, muttering something about “tolerance stacking.” They direct threaded one of their suppressors onto my MPX to test it, but even then it still shifted 4 inches to the left at 25 yards.

I’ve used my suppressor on 4 other pistols/pistol caliber carbines, with less than 3 inches of shift at 50 yards, so I don’t think it’s the suppressor. I also tried, on my MPX, 2 different tri-lug mounts, with the same disappointing results. Maybe both mounts are goofy. But I don’t feel like buying a third mount to find out.




Sent from my iPhone using Tapatalk Pro

[Clusterfrack]

Sig also more or less blamed the mount and suppressor, muttering something about “tolerance stacking.” They direct threaded one of their suppressors onto my MPX to test it, but even then it still shifted 4 inches to the left at 25 yards.

I’ve used my suppressor on 4 other pistols/pistol caliber carbines, with less than 3 inches of shift at 50 yards, so I don’t think it’s the suppressor. I also tried, on my MPX, 2 different tri-lug mounts, with the same disappointing results. Maybe both mounts are goofy. But I don’t feel like buying a third mount to find out.


I bet the threads and/or barrel face are not perfectly orthogonal to your bore. You don't have visible evidence of baffle strikes--yet. But I bet your bullets are skimming the baffles. If this was my gun, I wouldn't risk damaging the can--or worse, a catastrophic and dangerous issue. I've only seen a major baffle strike once, but it was bad, and I was right next to it when it happened. Do not want to repeat.

[nalesq]

I bet the threads and/or crown face are not perfectly orthogonal to your bore. You don't have visible evidence of baffle strikes--yet. But I bet your bullets are skimming the baffles. If this was my gun, I wouldn't risk damaging the can--or worse, a catastrophic and dangerous issue. I've only seen a major baffle strike once, but it was bad, and I was right next to it when it happened. Do not want to repeat.

I agree. My MPX is going to be a no-suppressor gun from now on, which is fine for my primary use of it. It’s just sad that such an expensive and otherwise awesome little gun has such a defect, and moreover that the company which made it thinks that such an imperfection is acceptable.




Sent from my iPhone using Tapatalk Pro