[Hugh]

I believe the reason the carbines had the extra spring in the forearm is because due to the extra mass of the bbl and forearm (in your case the extra weight of the bbl), the recoil spring has to be so weak for full retraction that it isn't strong enough to pick up another cartridge from the magazine and close the action. You can try a lighter recoil spring & handloads with a heavier bullet to give it more recoil, but I'm not sure this will solve your problem.