Mr. Doomsday is good!
Seleziona's replica pistol. Strong, powerful, and a replica. Here
i would build it but i dont have enough Y connectors
That sucks. That was the only gun that fits your discription that I could think of.
If you want a good knex gun that doesn't take a lot of parts, you should forsake realism as one of your requirements. Go build the Untangle.