I recently started modding(see:a few minutes ago) and it's really simple. So here's my first release, the UMP that fires as fast as a p90!
Don't mind the green people, that's RiceKing's totally green mod.
1.Go to your "Game" folder in your combat arms folder, and find GUNS_M_PV_SMG.rez, and create a backup(copy and paste it somewhere else).
2. Use RezInject(included in the .zip) and select your GUNS_M_PV_SMG.rez file, and inject the 4 .ltb files in the .zip provided.
3. Rename GUNS_M_PV_SmG.rezNew, the file you have just created to GUNS_M_PV_SMG.rez, and place it in your "Game" folder, saying yes when it prompts you to overwrite it.
4. Buy a UMP, find one in game, or whatever, and use the AWESOMENESS of it!