It will tighten up your groups!! I bought one for a new NEF Handi-rifle in 30/06, and played with it some, before I settled it down to where I wanted it! I really didn't need it, because the Handi-rifle is pretty accurate anyway.
I think I paid like $9.95 at Bass Pro in Shreveport, so If it didn't work or I didn't need it, I wasn't out much jingle!!!