Actually, not.
As a matter of fact, I've seen one example of a BR gun that had no threads in the receiver. The barrel shank area of the B.A.T. receiver was bored to remove the threads and a narrow 30 degree taper was machined forward of the locking lug abutments. The shank of the barrel was turned to a gauge fit to the receiver's i.d. with a matching 30 degree taper on the rear that mated to the taper in the receiver. Two pinch bolts clamped the receiver to the barrel shank.
This was done to test for possible gains from 'clocking' the muzzle and the guage fit allowed the barrel to be easily rotated to any position desired. The 'clocking' tests proved inconclusive but the barrel/receiver attachment method was a non issue.
The owner, an engineer that loved to experiment, took the gun apart to show me his work while we were testing prior to the Wisconsin State NBRSA Hunter Championships. His first shot on the sighter when we went back up was a solid '10'.
Good shootin'. -Al
What did the two pinch bolts do?