I'm trying to replace the case on a 38-55 CPA seater that Russ Weber built for me.  I've searched on here for info on the threads and it looks like 5/16 -32 tpi.

I took the case off and it's definitely 32 tpi, but the major diameter of the threads has a rapid taper on it, almost like npt threads.  It goes from about 0.319" to 0.294" over the 0.250" thread length.   

Is that likely to work with a 5/16 - 32 straight tap?  He did have a little bit of locktite on it.

thanks,

Chris.

Dave you might find this funny.  I'd actually meant to make a new case for the 32-40 CPA seater, not the 38-55 one, but I measured the 38-55 one.  I don't need to make a case for that one .

I realized this last night and measured the 32-40 one.  It's as expected, 5/16-32 nice and straight so that's a relief.   

Chris.