Prefit Barrel Won't Screw onto Action

[Red_SC]

If the tolerance class is not the same on both inside and outside threads, you will almost certainly have a problem that feels like cross threading even though it isn't.

Not to be pedantic, but that’s not accurate.
By my book, a 1-1/16x16 thread, both internal and external cut to class 3 spec must have .0000 to .0086 clearance.
Changing the internal thread to 2B changes your in-spec clearance range to between .0000 to .0102. It has the potential to be looser, but 3A and 2B will screw together.
Changing the internal back to 3B and dropping the external to 2A, your in-spec clearance range becomes .0015 to .0114. Again, a looser fit, but they still screw together.
I know what you meant, I just wanted to be clear. A class 2 and a class 3 will still screw together if both parts are cut correctly, even though they’re cut to different specs. The problem is when a gunplumber cuts a thread to minimum clearance fit using an action as a gauge, and calls that a class 3 fit without actually measuring the thread. Again, I’m not putting you in that category, I’ve been reading your threads for years and you know what you’re doing. Some of us machinists just take great joy in being curmudgeons.

 

[308pirate]

Not to be pendant if, but that’s not accurate.
By my book, a 1-1/16x16 thread, both internal and external cut to class 3 spec must have .0000 to .0086 clearance.
Changing the internal thread to 2B changes your in-spec clearance range to between .0000 to .0102. It has the potential to be looser, but 3A and 2B will screw together.
Changing the internal back to 3B and dropping the external to 2A, your in-spec clearance range becomes .0015 to .0114. Again, a looser fit, but they still screw together.
I know what you meant, I just wanted to be clear. A class 2 and a class 3 will still screw together if both parts are cut correctly, even though they’re cut to different specs. The problem is when a gunplumber cuts a thread to minimum clearance fit using an action as a gauge, and calls that a class 3 fit without actually measuring the thread. Again, I’m not putting you in that category, I’ve been reading your threads for years and you know what you’re doing. Some of us machinists just take great joy in being curmudgeons.

I hear you. I just don't often have time to teach the class.