KC, the best way to find out the effective range for these rifles and loads is to shoot them over a chronograph and plug in the velocity and BC into a ballistic calc. And then actually shoot them for accuracy potential and drops to various distances out to where the bullets should be reaching about 1800 fps, which is probably their effective opening velocity. You should be able to find that info on the manufacturers web sites. Take their BC with a grain salt. I would say 800 yds is probably pushing it with the 300 WSM
and the Barnes bullets.
The 300 WSM is probably shooting 180's in the 2950-3000 fps range. HSM has some Berger 185 hunting VLDs they list @ 2990 fps. You might try a Hornady Superformance load for better velocity.