God groups but bad ES
I have a custom built 300 RUM that I had built two years ago that It shoots sub 1/4" MOA from 100 to 700 yards (3 shot groups); however, when I use my chrono, it shows an ES of about 25 fps. Even if I throw out the most extreme velocities, it would still show an ES of 20 fps. What can be causing this?
When I shoot at 750 yards, the groups tend to be slightly more horizontal than vertical.
Here are the specs of my rifle.
Stiller Predator Action
Schneider P5 barrel, 1:11 twist -
5.5 taper, 28"+ Muzzle Break
McMillan A 3-5 Stock
5.5x22x56 Night Force
86 grains of H1,000
Federal 215 M Primers
Berger 210 Hunting VLDs
loaded .020 off the lands
OAL is 3.798 (4.127 with comparator)
2,988 to 3,013 FPS
I measure every load exactly on an older RCBS Balance Beam scale
RCBS rock chucker press
RCBS full length dies and seater
Just as an FYI, I have no problem achieving a low ES when I reload for my friends 300 RUM (6- ES), or my Kimber 300WSM (9- ES); however these guns only average .75" group at 100 yards.
The other thing that is throwing me off is when I last shot at 750 yards; I shot 3 groups that were (1.5") (3.2") (2.5"). When I do the math on my Ipod (ballistic FTE), and figure a 25 fps ES, my bullets should be printing in a 6" vertical group.
I know I should be happy with what I'm getting, but I can't help but think what my 1,000 yard groups would be like if I had an ES of 5?
Where should I begin my search for th cure?