Wait no further, here are the initial testing results, very promising
Power is roughly the same as my other prototype, I figure that because of the tapered cartridge, it unseals the breech moments after startring to move so air is lost out the back. On the plus side however, the effort needed to seat it completely is very low, meaning there's a greater chance of chambering a fresh cartridge successfully.
Some 1000 frame per second testing, here it is with a steel BB and no restrictions at the breech:
Again with a steel BB, though this time with a marker pen as a bolt, and rubber bands to keep it in place. As the rubber bands are skewed, they flip the bolt out on firing:
Steel BB and double the amount of rubber bands, this time the bolt doesn't make it out of the breech but there's enough force to snap one of the bands. What's significant is that there was enough bolt delay to allow a new cartridge to be chambered were it fitted with a magazine, and the botl had more than enough force to hammer the cartridge into the breech:
Some further tests:
.</sup> 1 - steel BB with 2 skewed rubber bands at 420 frames per second
.</sup> 2 - steel BB with 2 counter supported rubber bands at 420 frames per second
.</sup> 3 - lead ball with 2 counter supported rubber bands at 420 frames per second, this time it tears the bands and the bolt flies right out.
.</sup> 4 - steel BB with 2 counter supported rubber bands in real time (and yes, I sometimes enjoy working with GlaDOS chastising me in the background
In view of the above, it certainly seems work building a proper bolt, ejector and magazine, hopefull I'll have that done for testing tomorrow. In the meantime, here's a detail of the current setup astride the modified cartridge: