You should be averaging about 2700 FPS in that 21 inch tube with 50 grs. of H-4350 , not 3050 FPS..I suggest that your chronograph is on the blink or perhaps your guessing and by goshing or have been misinformed...
I have chronographed hundreds of that particular load in a number of 7x57 rifles over the years. That is a rather mild safe load btw..I have loaded the same with considerably more of the same powder and same bullet and not reached that velocity..??????????
The chrony isn't on the blink as that on the same day an 8x57 with a 18.5 inch barrel got about 150 fps less than what the book said it should get for a particular load. That is roughly correct for a barrel of that length with that load.
I think you're a little conservative on your estimation of what it should be getting. JB said in article 2900 was easy to do in that bullet and I've seen lots of people on this board claiming 2900 with that bullet and combination.
Oops, I was misremembering a bit. At lunch I got my load book. It was 51 grains that averaged 3057. 50 grains averaged 2991. A little different, but not much.
