Been doing a crap load of testing with my new Chrony F1 since december, in my basement, and have been seeing really odd issues from night to night. I have it set up under a regular bulb, and have the diffusers on to make it actually work every shot.
What I've noticed, at first with my CA M24, is that one night it'll chrony at 525ish, and all rounds tested sit within 5-10fps of that, the next night without any changes it'll chrony 508ish, next night 487ish, next 505ish, etc. etc. Been noticing that with my MP5s as well, one I downgraded and had it shooting pretty well between 320-330fps, two nights later it was 300-305fps. My other one I spent all weekend rebuilding it, and once done had it sitting quite happily at 385-395fps, got a couple 398, 399s in a string of 20odd shots, then one 403fps. Totally legal for field use. Next night I ran 10 or so shots through it, the lowest I got was 410fps and the highest was around 418fps or so.
Funny thing, I test BB Bastards with my TM MK23 springer and it NEVER changes, always sits around 215-220fps with 0.20g. Not sure if what is varying is where I put my shot through or not (MK23 is always shot consistantly because it's shot and easy to aim over the sensors, but the AEGs and bolt action are difficult to get consistant paths with. And I don't think light is having much effect since I did a bit of chronying with my MP5 using sunlight and it showed similar results. And it's a recently installed battery (albeit cheap ones, don't know if these require high quality ones or not).
Any thoughts? Nothing changes from night to night except maybe the temperature (is my basement, unfinished....... )