Just purchased a Tactical 16 and have a question about the ammo. Can I use the Hornaday 75 gr BTHP TAP steel cased practice ammo without it causing any harm to the gun or does it have to be brass cased?

Some people prefer to only shoot brass. But its up to you. Steel case won't hurt it.

I shoot both and whatever my ammo buddy has the best price on. The only real negative that I have experienced is that the steel case ammo is alot dirtier so to speak. It will really grime up an AR. Ive only had a jam a few times but it was in a Rock River, never in any of my Spike's.