Originally Posted by AS92-RD
You could use a heavier BB, I'm sure that would slow it down.
Yes, a heavier BB will lower the velocity. But it's not about velocity. It's about energy. A heavier BB at a slower velocity still has the same energy as a lighter BB at a higher velocity. That's why when there's a limit on a game, it's specified that it's with .2g BBs. My M15 rifle shoots about 385 with .2, and about 320 with .28. Even though that's a lower velocity, it still delivers the same energy.
So if you want to game it, you have to downgrade it to under 400 for outdoors, and under 350 for indoors. That will require replacing the main spring.