Not sure. The drawings I've seen show a 6 deg. taper into the rifling from the case mouth Probably on the reamer.
The 38-55 has been pretty wild with variations over the years. Factory grooves anywhere from .377 to .382 that I've seen listed. I've seen some posts with later Marlins at up to .381, makes it hard to fit the groove if the loaded case won't chamber(.382 + (case wall thickness X2) trying to fit in the neck area of the chamber). JES goes against tradition with the .375-.376 dia., supposedly so you can use .375 Win jacketed bullets. The purists object, but I don't plan on using any jacketed bullets so it really doesn't mean much to me. I'll fit to whatever the groove is anyway with cast bullets.
In this rifle I've tried 4 powders, and bullets from 2 different molds as well as pan lube and powder coat. Haven't found one combo it didn't like yet.
You can run cast up to around 2K with this case if you like recoil, just don't see the need at woods ranges.
Last edited by Ole_270; 10/10/16.
