So I just got a new 300 wsm (Browning X-Bolt, love it!) and am working up an elk hunting round. I just spent some time at the range today with handloads and my velocity is nowhere near what the reloading manuals list. For example, the 180 grain x-bullet was supposed to generate 3036 at the max load of one powder. I got 2866. The 200 grain accubond was even worse--almost 200 fps lower on 3 different powders. Anybody offer any reasons why this is happening? Here are some observations on the day:

-Very windy
-Top loads did not necessarily develop top velocities. For example, one grain less than max gave best velocity from IMR 4350. This was true for 4 of 5 powder/bullet combinations I tried.
-None of the loads showed excessive pressure signs
-Weird clouds out. Very thin, high clouds. Maybe they affected my Chrony?
-FYI I would have expected not to hit top velocities as my barrel is 23" vs 26" test barrels. But 200 fps lower?

Any insight would be great, thanks!