I just emailed Green Mountain to confirm land and groove diameters of their .44-77 barrels, and here was the reply:
Good afternoon,
Thanks for contacting GMRB,
The bore and groove dimensions are as follows.
.436-.438/.445-.4465
Do keep in mind our barrels are produced in lots of 100 pieces or more, so if you are looking for an exact measurement of the barrels bore or groove, you will have to slug the barrel.
Kind regards,
Have you .44 shooters found this much variation in the GM barrels? Asking in order to make the right choice on PP bullet mold/swage dies.