I have an fx impact mk2 22 600mm I am having fps change overnight I noticed when I shot today my group has opened up and moved I had it dialed in at 904fps average with low being 901 and high being 908 but today I shot through the chronograph and it was 920 avg with low being 915 and high being 923 this is the 4th time this gun has done this and it's getting annoying having to retune everyday 1st group was today and 2nd is yesterday both at 50yds