The fact that you had to add shims to complete the reset means there is still some bolt stick issues. If the bolt fires or chuffs, but won't reset, it means the spring tension cannot overcome both the residual pressure and the friction. The residual pressure by itelf should not be an issue, because the bolt has already vented the excess air and has attempted to reset. It can't reset because the friction is still too much. You will need to solve that issue or you will risk a sticking issue at the most inopportune moment during play.
Except for the Automag in front, its usually the man behind the equipment that counts.