Bellydeep my results are about what TexnCal is seeing with his rifles. I have used some customs and factory 300 Win Mags modified for a 3.6" box and bullets seated to longer OAL in the 300 Win Mag....with that arrangement and 24" barrels slightly over 3100 fps with the 180 gr was routine....and in 300 Weatherby's with 24" barrels you won't see much more with hand loads.
All my 300 Weatherby's have been M70's either customs or factory Classics and generally I have seen about 3150-3175 with app 85 gr 7828 and 180 gr bullets.
Ultimately the 300 Weatherby is faster but a lot depends on barrels. I had a 9 twist .309 groove 26" Krieger SS barrel in 300 Weatherby that would do 3250 with a 180 . OTOH a 24" McGowen barrel did no better than 3125 with 180 and there was not 60-70 fps that separated it from the 300 Win Mag and 300 H&H that I also had in the stable at the same time.
Also had a pre 64 M70 that was rechambered from 300H&h to 300 Weatherby that showed 3420 with the Weatherby 165 gr BT factory ammo. The Weatherby stuff is loaded pretty hot.
I spent an afternoon last fall sighting in a pal's rifle, a custom 300 Weatherby with 25" Krieger and it routinely gave 3050 with his 200 gr AB hand loads. That's about 100 fps better than the best I ever saw from a 300 Win Mag.
In the end, I think the others are right...100-150 fps difference between them seems about right.
