Now how do I save the modded gun for it to be a playable in the blood gulch map?
Here's what I've done so far.
1. Opened up bloodgulch in halo mapping tools.
2. Opened the entity then navigate to weapon tag then click the + sign then find the weap and click on it
3.Then find where it says proj on the left hand side and right click swap then click the drop down box and find the other bullet you want.
(kinda copied + paste what you said.

)
Sorry, I'm new at this and pretty clueless at this.
Thanks.