Big shift in POI with suppressor

[Endall]

Was running a Yankee Hill suppressor on a Walther SP22. No noticeable shift in POI. Found out my S&W 422 has a threaded barrel.
Installed the adapter and suppressor. Tightened up adapter the same as original barrel, very tight. Took out and sights were still spot on. Installed suppressor and now POI is off 6 inches high and left.
Grouping is still tight. This is at 12 yards. Took suppressor off and back to spot on. Reinstalled and tightened up suppressor on adapter really tight. Still high and left.
The Walther has zero shift. S&W 422 so much I hit a 6” plate once in 10 rounds from 12 yards. Shifted aim low and right. Ran off 30 in a row. Removed suppressor and shifted sight to center and ran off 20 more.
Six inches at 12 yards is crazy. Will check to see if suppressor is cocked off by the thread adapter.

 

[Odd Job]

I had that on a .22 rifle with a bad adapter. The target was at 25m and no rounds were going on paper, they weren't even on the target backing or frame. Might have been clipping a baffle, I don't know. There was no obvious damage to the suppressor or adapter.

You can get POI changes even when using multiple suppressors of the same make and model on one rifle. I have a thread on it somewhere here on THR... however, the changes are not as drastic as 6" off at 12 yards. @MachIVshooter will know more about the possible causes, no doubt!

 

[MachIVshooter]

Though it will usually cause groups to open up, a POI shift that dramatic on a fixed barrel firearm can really only be caused by bullets contacting baffles or end caps.

The thread adapter on the 422 is a barrel nut and seats against the face of the frame. If that face isn't perpendicular to bore axis, you get axial misalignment. Doesn't take much with a can, couple thousandths from one side of the adapter flange to the other.

 

[Endall]

Contacted the seller of the adapter. They recommend torquing to 25 in-lbs. Factory barrel nut felt like 50 ft-lbs. Pulling the adapter and going to torque to 25 in-lb. Then shoot to see if POI changes with of without suppressor.
Definitely will need LockTite at the tension. Finger tight is at least that high.
Found another supplier. Think I can hear a metallic noise. But can cleaned with only carbon. Might be shooting shavings out.

 

[Endall]

Installed a different thread adapter. Made up a little past bottoming out. Now 4 inches high dead center. At 12 yards.
Guess frame is not true. Will try hand right with LocTite like original barrel nut manufacturer recommended. Thought I heard a ringing when tightened up at first.
I hoped original barrel bushing was defective. Instead issue appears to be my 169.00, 35 year old gun.

 

[Endall]

Will try the Odd Job advise, have another Yankees Hills 22LR suppressor. But since Walther SP22 shot exactly the same POI with the same suppressor it is difficult to blame the suppressor.
SP22 was easier to shoot with suppressor. Could use the suppressor like a sight rail. The S&W 422 barrel is low, cannot see the suppressor in sight.

 

[Endall]

Tried a half dozen things. Even reinstalled the lock washer that was under the factory barrel but. Both thread adapter. Both thread adapter manufacturers said leave out.
They were right. Shot even worse, eight inches shift at 12 yards. But while removing washer accidentally knocked barrel loose in slide. Very tight fit, cranked in with thread adapter. POI shifted a couple inches. But suppressor now only shifts POI 2 inches or less. Can live with this.
The original barrel nut was super tight. I may have not seated it in the slide quite was tight.