Drill and tap a hole perpendicular to the windage screw that would allow a set screw to be tightened against the diopter body. You can line up the new hole with the 0 on the windage scale, but come from the backside if there is enough material there.
1/2-28 is fine for 7mm.
Some suppressor manufacturers site possible side load weakness if the rifle is dropped on the suppressor, on the smaller wall thickness for their reason to recommend larger threads.
It could be a worn sear, trigger pin, hammer pin, or broken/bent spring on the slide release. Also check the tip of the hook and hammer abutment for any burrs. The hook on the slide release is intended to pull the hammer back off the sear when racking the slide to prevent slam fires.
That works! I'll keep doing it my way though. I'm not going to rely on loctite alone, without at least some kind to shoulder for the collar to register against.
Also, the way I do the permanent adapters, there's no tolerance stacking either.
For a collar with no adapter, I need an O.D. of .65" or greater. A standard Tikka barrel is .62" at 24". You probably have smaller threads on the barrel itself, judging by the length, probably 9/16-24, and 5/8-24 threads on the end of your adapter.
I haven't considered it, but it would be up in the Whidden price range for a small shop to do. Custom ground reamers are $250-450 depending on who makes it.
Yes, measure how much pin is sticking out of the breechface. Shotguns are usually in the .055"-.07" range. Also inspect for damage, sharp edges, squared off tip, etc..
I think the pins are still somewhat available for those for a reasonable price.
Check the model number, I think those shotguns are Marlin Model 90s.
Firing pin protrusion is the first thing to check. Pull the barrels. Put a piece of delrin, plastic cutting board, or hardwood over the breech face and release the trigger. Don't dry fire without something to absorb some...
I've got stainless or blued Tikka .308 barrels available for $100. They're off of standard models so no flutes to deal with. I can set them up with whatever threads you want. $125 standard threading, $175 for 5/8-24 with a shoulder collar. Max barrel length for collar is 20". Can also set up...