Caliburn B Variant V2 K31+K25 Double Spring Rest

With a K31 and K25, I'm hitting about 300. Not a huge increase from my single K25, which was hitting at 285 fps. It's probably because my barrel is kinda gunked up from using too much lube on the ram orings.

Also, if you find the prime getting stuck halfway in, chamfer the inside back end of your plunger tube. It's probably getting stuck right there.

Print with 5 walls at 50% infill. You can probably get away with 30% infill, but I like to be on the safe side. 

Just a note, I modeled this part with a K25 that was just under 10 inches and a K31 that was 11.5 inches, so depending on the length of your spring, performance may vary.

Added a double spring rest for the Caliburn B variant V2