There are currently no SAMMI specs for the 38-55, it is considered an obsolete chambering. The old standard was .380 on the groove, .375 on the bore. The cartridge all but died; I may be wrong on this, but I believe even Winchester had at one point stopped making ammunition fo it. With the CAS shooting crowd and the resurgance of interest in all things old, the 38-55 found itself being sought after once again. The makers foudn themselves with a ready market.
Problem is that there are no working standards to go by, so anything goes. Winchester, Marlin and NEF use what seems to be (least so far as user reports go) a chamber that is sized to the .375 Winchester that may or may not be lengthened to the original 38-55 chamber length. The case headspaces on the rim so chamber length is not crtical, so long as it is long enough. The 38-55 is about .050 inches longer than the .375 Winnie (Don't slam me, I didn't bother to look up exact dimensions, working off the top of my head instead) and has a different case taper. The 375 has a fatter taper supposedly preventing it from being chambered in an older 38-55 since it is a high pressure round.
Lot's of people have had trouble out of all three makers. Each claim that their chambers are cut to specs, but since SAMMI has no specs on the 38-55 it begs the question of whose specs? Barrel dimensions suffer equally with reports of .377 to .381 being made by each manufactuer. Since there are no current specs on this chambering, the problem is not the makers proving they are right, but the customer proving they are wrong. What a hell of a way to run a business.
EDIT: There are also chamebrs that are tignt, it seems that 38-55 chambers are found but reloading dies size to 375, not 38-55 The problem is messy, messy, messy.