I was shooting my USP tactical today.  It was sighted in perfectly for Fed American Eagle 230 grain, my main practice round.  I wanted to check the POI with Ranger-T's, and when I shot them, the group was centered about a half inch left at 10 yards.  Could this be  due to differences in the ammo, or is it more likely just a fluke of a group? It was only 1 mag of 12 rounds.

Yes, it could be the difference in ammo.  My experience has been that ammo types and brands will definitely change POI.  Some will give smaller groups and some will give you more of a pattern than groups!  But to be sure about the Ranger T's you will need to shoot more that 12 rounds.  Try a box or two and see what the POI is like at that point. If that's going to be your defensive load you may need to adjust your sights.

I haven't decided on my carry ammo yet, but when I do I'll readjust my sights for that specific load.

gunfighter48
A 45 may never expand but it will never be less that .45

Yeah, I certainly could see shifts in POI from ammo types, but this much sideways?

Quoted: Yeah, I certainly could see shifts in POI from ammo types, but this much sideways?

Yes, changes in torque loading occur too which causes what appears to be lateral shifting of the group.

Notice that the pistol does not recoil straight back when fired but rotates right too.

Ammo.

So today I shot the USP compact with the same two loads-- I actually forgot the tactical...  In any case, the two points of impact were identical.  That makes me think it was probably just a weird group with  the TAC.  Any thoughts?