Self-loading self-sealing RSCB mag for foam darts [Proof-of-Concept] 

Self-loading self-sealing breach for foam dart RSCB mag. @hotkoin and @Shrub having been refining their own (quite different) designs for dart-sealing RSCB's, so figured I'd see if I could scale my one down for .50cal short darts.
Original proof-of-concept was for LPA-launched ø54mm Blu Maxi BFD's... this just tidies the idea up for use with smaller ammo: • [Proof-of-Concept] RSC...
In essence, operation is similar to the "Aperture Cup": • Aperture Cup
Basically a flexible rubber tube (here using a "balloon art" balloon) connects the breech and a short length of sleeve that is free to twist but allow darts to pass through from the mag tube.
Twisting the sleeve relative to the breech constricts the rubber tube, making it seal to the round immediately behind the one in the breach.
When the tank's dump-valve is released the round in the breach is fired - but without the pressure having to first fill all of the dead-space in the mag tube around the remaining rounds.
When the sleeve is untwisted the rubber tube un-constricts, allowing the next round to be pushed forward into the breach by the mag spring.
Because the mag tube behind the seal is effectively out of the picture, this should mean you don't need to seal the other end of the mag - opening up a number of options for re-loading.
With minimal dead-space, every round fired should be receiving the same volume of air at the same pressure, and with the 2nd round in the queue held back until the sleeve is released the shot being fired will receive the full burst of pressure without the next round plugging the breach early. Short story: shot strength and consistency should be markedly improved.