I know, the Vive grabbing issue is a pain.
I didn't want to modify the grab system for that, because this is just a demo of the overall mechanics.
For grabbing weapons I am going to have sticky grips, even on Oculus, the reason being that I use the Grip button for reloading. So this will be fixed for you in the next build. Right now I didn't want to build a new unpolished system since converting to SteamVR caused a truck load of problems already.
Shells are limited to 20 per type, and they are spawned only when you start the game, they are always there. Once they stop moving they should have very minimal impact on processing including graphics since they vanish pretty quick at distance. I could possibly change the limit or give the option to change the bullet limit.