shooting at different tempetures

SHOT YESTERDAY AFTERNOON AT 98 DEG. THIS MORNING AT 64 DEG. I WILL DO 2 PICTURES AT A TIME. 15YDS. I have a Diana Stealth. I’m using H&N hunter trophy target 14.66 gn.
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My HW97 behaves pretty similar, but maybe not as extreme as you are seeing. At this winters field target matches I would get a 3moa shift from 40f to 70f through a match. It is just something you have to learn about your rifle. I was able to duplicate it at the house on cool days by going outside and shooting as the gun cooled down the poi would change. 

They did a short test of some rifles on American Airgunner last season at room temp then out of a deep freezer. Counter to what the advertisers are saying, the Nitro piston rifle they had on hand had way more of a velocity shift than the spring gun.