Okay so new dilemma.I finally bought a Chronograph a Caldwell G2 Ballistic Precision. And thats where it all starts.

My favorite load for my AR had 2 strings measuring ~2550 FPS and one measuring ~2280. All had standard deviations of around 10~15. (which I assume is not bad but not great??)

Question is how did I have a sudden string 300FPS lower?
Could I have aimed slightly differently?
Keep in mind that the 50 bullets (5 Strings) came from the same batch. I make 50 at a time and package them. Case lot, bullet lot, powder lot, primer lot all the same. Bullets were chosen at random.

Ammo Spec: Hornady Case, Hornady 68GR BTHP, Varget 24.3, CCI#400. COL 2.250





Dilemma #2
I have a second load for plinking 55GR FMJ. It is reading horribly. All strings have SDs of 200+ with a spread of 440. FPS ranged from 2500~2900.

What the .... happened? Same batch for all strings.
Im assuming wrong powder for the bullet?

Ammo Spec: Winchester Case, Horndady 55FMJ, Varget 26.7, CCI #400

I don't load for those calibers but I can tell you the light conditions will affect your velocity readings. I got as much as 100 fps variation from one day to the next with the exact same load. So, I switched over to a Magnetospeed and now a Labradar so lighting conditions don't affect anything anymore.

Beyond the chronograph, switching lots of powder can make a big difference in velocity too.

Had nothing but problems with all 3 of the caldwell Chrony's I tried. Finally gave up. Had very similar results as you had. Went back to setting up the big Oehler until I got my hands on a LabRadar.

How far is your first screen from the muzzle?