Just a thought....
I wonder if the carrier may be modified for a shorter cartridge? Say a machine screw drilled into carrier to serve as shell shop. It has to be high enough to stop the rearward travel of a shell coming out of the magazine tube and short enough such that when the carrier is raised, the bolt doesn't strike and jam against it.
Vigilantibus et non dormientibus jura subveniunt. Molon Labe!