I'm a little confused. When I look at Bergara's lineup, B-14 is an entire series of rifles.
The B-14 HMR I understand (can't find an "HMR-14"). Your second rifle, "B-14", I have no idea what that is.
Do the bullets have the same ballistic coefficient? Are the rifles zeroed identically? Same rifling twist rates?
ETA: Looked further:
The Sig ammo appears to use a Sierra MatchKing hollow-point bullet, made for precision shooting. BC - 0.535
The Nosler Ballistic Tip is an expanding bullet used for hunting. BC - 0.509
Have you tried switching ammo in the rifles to see if they're close using the same ammo?