New to this site...and I don't own or use a powerhead, but in answer to the question of Rifle vs. Pistol...the rifle cartrige will always be a better choice...and if you can use one with a good punch and small diameter bullet(less space=higher velocity) like one of the following: .223/.270/7mm Rem. Mag, you will knock the **** out of your target!
BTW for those of you who know me the answer is YES I am still stuck in afghanistan
and our .223's (m16) do a good job on Taliban soldiers anyway. Later ,Eli