Help. Suppressor Accuracy Issues, Wildly Inaccurate.

[fivefivesixphoto]

I have a Sig MPX, an AAC Tirant S and an AAC Tirant. While unsuppressed my MPX is very accurate but when I put on my suppressor (either one) it is wildly inaccurate. I don't mean it has consistent POI shift, I mean it's shooting all over the place 6"+ off target at 25 yards. There are no baffle strikes. I am using a direct thread and the fixed barrel spacer. Any idea as to what might cause this type of issue?

[a_canadian]

You say no baffle strikes, but often a bullet can graze a baffle or two or just the end cap and leave very little if any evidence. I'd suggest an alignment check with a fitted brass rod, something which just neatly slips into the barrel and when rolled on flat glass shows perfectly straight. Another option would be to put taping brittle target paper across the end of the can, securely, then shooting one round. May have to punch a small hole in it to prevent it blasting free. If the hole is at all off center you'll have your answer. My guess is the barrel shoulder isn't perpendicular to the boreline.

[rimshaker]

From what I remember in pics, the new Sig barrels are tapered and don't have conventional shoulders.
Which should be fine anyway since they have metric threads, and metric pistons index on the muzzle.

Have you tried looking through the barrel with the Tirant attached to visually check alignment?
Are you using factory ammo or reloads?

[CanOfWhooppass]

Have you tried a variety of ammo with different weight bullets?

Since you align to the muzzle, was it clean of carbon?

[T-Rex]

All other posts aside, what caliber are you shooting and what are the calibers for the suppressors?
Just trying to put some perspective on allotted tolerance for error.

[mbogo]

The change in barrel harmonics wouldn't cause a 6" shift in POI at 25yds.

Have you checked the muzzle end of the suppressor for evidence of bullet contact (in good light with magnification)?
Have you check that the muzzle of the rifle was threaded concentric to the bore, or alignment between the bore and the suppressor?

mbogo