.22 LR snap caps. re-use spent casings and insert snap cap into casing. 

smaller then actual projectile to reduce jamming.

use old casings, the reason being, I have found that just PLA likes to jamb in rifle so made and remade and remade until i decide to just re use spent caseings, so that the extractor will actually catch and not let go or break plastic . 

L=20.83

W=5.26 

L of cart+snapcap=21.44

default speed 100.0 mms

temp 215/60

infill 10%