i have an idea for a rile that i want to make for shooting targets

i dont really want to use a spinkler valve and i wnt something that hopefully wont release all the pressure in the canister all at once.
the idea behind this is that once you pull the trigger it releases the bolt and that shoots back and then foward again releasing enough air to propell a bb/pellet.
any ideas on why it wont work??
cheers






