Star Rival Apollo 15KG Spring

The Star Rival Apollo 15KG Spring is a drop-in upgrade spring for the Nerf Rival Apollo, rated at a heavier 15KG — noticeably stronger than the springs used in the smaller-dart Star lineup, which makes sense given the Apollo fires solid Rival rounds rather than foam Stefan darts and needs more force behind each shot.

Fitting it is the same as any Rival Apollo spring swap: it's a direct replacement for the stock spring, no shell cutting or extra parts required, so you can get more push out of your Apollo without turning the internals swap into a bigger project. At 15KG it's aimed at players who've already got the basics of an Apollo teardown down and are chasing more output from the round-ball platform specifically, rather than a general first-time upgrade.