MM Firefly 5KG Main Spring

Running a field with a strict FPS cap, or handing the Firefly Blaster to a first-time shooter? The MM Firefly 5KG Main Spring is the lightest spring rate Monkee Mods offers for the Firefly platform, chronographing at around 80 FPS with Worker Gen 3 Darts — comfortably under most indoor and youth-friendly limits.

It's a direct drop-in replacement for the stock spring, so no other internals need to change to bring your Firefly's power down to this level, and installation follows the same process as fitting any other Firefly main spring. Because it's a genuine spring-rate swap rather than a dart-weight trick, point-of-impact and cycling feel stay consistent — you're just dialing back the output. Pair it with a heavier spring later if you outgrow the low-FPS setup, since Monkee Mods carries the Firefly spring lineup right up to 12KG.