Odd POI, how is this possible?

I was at the range this afternoon shooting a Steyr .308 rifle at 100 yards. Eventually I ran out of target spots I placed on the board so, with a few rounds of Hornady Match left, I went after someone else's left-over black dots.

The first picture shows I managed a decent 5-shot group just about 1/4" into, and below, where the black dot was. With a target change pending and only 3 rounds left, I moved to another black dot about 12" above this one.

Not a terrible 3-shot group but, how on earth is it an inch or so lower on the target board than the previous group?

The only thing I, and a few range pals, could figure is the target boards lean backwards maybe 15 degrees or so. That still doesn't make sense to me, I'm aiming at the dot. Maybe the barrel reached a heat point after the first 5 where it just started dropping the rounds a bit lower? BTW, it was on and off raining all day, maybe the rain drops forced the last rounds lower

Anyone else notice a change on POI just from aiming at different point on the target board?

jmr40 said:

How long between shots? 8 rounds in a fairly short time could cause a shift in POI.

Click to expand...

15 minutes.

Since several folks mentioned parallax, the scope in question is a Vortex Viper PST FFP, 6-24x50. I had it on about 12x for this session.

The side focus knob was, and always has been, set at 100 yards since that's the range I shoot at these days, and the target has been verified to be very close to that distance by range finder, within a yard or two. I'm not sure if the side focus knob is the same as parallax, if not, I don't know what else to adjust.

After re-reading jmr40's question concerning time between shots, and my response, I don't know what I was thinking . The 15 minutes I stated is the amount of time from when the range goes hot to when the range master gives the 3 minutes until target change notification, after which the range goes cold.

So, to more correctly answer the question, I shot the first group of 5 during the 15 minute regular time. I had 3 rounds left when the 3 minute notification aired, I decided to take a poke with these at the black dot shown in the second picture. All three were dispatched within the 3 minute remaining window.

My thought is that since the first 5 shots pretty much demolished the first black dot, the second group of 3 shots should have done the same to the second black dot. And, if the rifle started stringing from heat, that the second group would not have been as tight as the first. Instead a small, but noticeable shift in POI was observed when the only significant change was POA. It begs the question that if I'd continued to shoot the remaining 3 rounds at the first POA, would they have been low? We'll never know.

This isn't the first time where I've noticed groups having different POI on a target board with different POA's, just the first time I got a picture of it.