Is my chronograph wrong?
I just finished chronographing some .223 loads and the results are dissapointing. I used 25.3 gr H335 under a 55 gr Hornady SP with a CCI 400 primer. Hodgdon's manual said that the load produces 3203 fps.
Well, I didn't even come close to that velocity! The five shot average was 2875 fps, with and ES of 71 and an SD of 27!
I use a Lyman beam scale and weighed each powder charge.
My rifle is a Ruger SR556E with a 16.12", 1:9 twist barrel. I was expecting a bit slower speeds than the manual, but not 300 fps? What is going on here?