Merkel’s RX-Helix represents a new flexibility in parts interchangeability. A single receiver serves as the basis for a multi-barreled rifle in standard or magnum calibres, but the changeover can be made faster and more easily than ever before.
The last Merkel bolt-action repeating rifle I reviewed was the KR-1 , a telescoping turnbolt like the Mauser 66 which had had a solid rotary-locking bolt head with six lugs locking into the rear end of the barrel. The system had short travel, fast locktime and barrels were secured by a pair of integral screws with captive nuts. At the time, this was Merkel’s way of designing a switch barrel rifle, but other Germanic rifles used different methods of attaching and changing barrels.
With Mauser Model 03 for example, the barrel is easily removed by taking out two screws and it mates to a precisely-machined bedding block that allows sure return to zero. Other rifles make use of a split receiver that clamps tightly around a smooth barrel shank when a pair of screws are tensioned. The Blaser R8 uses an Allen wrench with a T-handle to back-off two captive barrel attachment screws, and the Sauer 202 uses a similar system.
All of the Teutonic switch-barrel rifles that I’ve tested including the Blaser R8, the Mauser M-03 and Sauer 202, have alloy receivers and bolts that lock up with abutments within the barrel rather than the receiver. Having the bolt lock-up within the barrel may be a more complicated breeching system, but it reduces the components that absorb firing stresses – the pressure at ignition – from three to two. And by doing away with these firing stresses, the receiver which acts merely as housing for the bolt-trigger and magazine can be made of aluminium. This also reduces weight. The Sauer 202 is one of those using a smooth barrel shank which is a slip-fit in a split receiver ring where three bolts cinch it up tight. The Blaser R8’s barrel attaches to the stock rather than the receiver, allowing the latter to be made lighter because it is subjected to a minimum of stress.