Mine went into the shift window in the afternoon... we turned up and it was cold, by the time i'd ambled to the lane, the temp had climbed from 14 degrees at 11:30 to 28 degrees... i instantly made a decision to work with the +28 degree shift point, any my 3 early misses were bang on horizontal, click perfect (even better than Ozzy's early miss, which was a pellet high
)... it went up to 32 according to the scope temp strips, but held (like it normally does)... however, later in the afternoon, it dropped down below 28, right down to 22, where I needed to use my experience and judgement to call when it had come back down. It didn't cost me a shot I am happy to say.
What I am also dealing with is a pressure/temp issue on the walther where she seems to climb 3/4 MOA(ish) at a certain point, but I am still unsure if it's overfill pressure doing it, or temp, because both have occured when I've seen it. But I think apart from 3 misses, I could see plainly them all land and i didn't see anything odd.
I checked a few ranges in conversation during and after the shoot, and they agreed with 2-3 other shooters, even though i had and hadn't been taking into account temp shift at different times of the day.
It was one of those days where i'd like to have roasted her and kept her roasted. She gains and loses heat quite quickly, within 10 mins or so, so for days like Harriers, she does need an eye kept on her... but I think these are quite rare... you'd need the combination of an exposed course, with a changing temperature... in summer, it's likely the ambient wouldnt move up and down so much in a day, and in winter, you'd probably not get her up to 28. So far, that's only occured at 2 shoots.
From talking to Alan, it seems the PMII behaves in a similar manner, with a switch like shift point, either side of which she is stable. I had mine as low as 3 degrees, and she was fine, but I don't know what happens lower than that.
I have found that mine reads 2.5 yds (ish) at 55yd short on bright white paper targets, so they are out of the equation for rangefinding at plinking ranges now.
As Dave says, the wind was my biggest issue, but then it's harriers and I've always struggled there with that sort of wind across those lakes. I think perhaps gun shift was probably more predominant.
You'll still have to prise her off me... and my first port of call would be a march, but then it's down to your taste and wallet... i've started digging through H's jewelry collection and looking up local pawn shops... one of those 80's in silver and another 60 for the springer would be nice hey