Ok here's how you would do it. It won't hit you if you stand behind a wall.
1. Go into "pak0.PK3" (makes it easier to look at with PakScape, get that at
http://www.MOHAACREW.com)
2. Go into the folder "models"
3. Go into the folder "fx"
4. Open up the file called "m2fgrenadeexplosion.TIK" with NotePad
5. Edit the radius
* To edit the Bazooka and Panzerschreck into nuclear bombs just edit the "bazookaexplosion_dm.TIK" and the "explosionPANZERIVshell.TIK"