CW: The old comparisons of the 7mm's kicking less than the 300's were generally made between the 7 Rem Mag and the 300 Weatherby. We know which one wins there.
We have a lot of 7mm magnums and 300's today and it's true you can heat up some 7 mags to the point where it's hard to tell the difference.I ran into a few boxes of 7mm WSM from Federal with 160 gr bullets that averaged over 3250 fps and turned a Kimber Montana into a nasty, disagreeable monster....with handloads at 3050 or so it was fine.
And many 300 Win Mag factory and handloads don't give any more than 3000 fps with a 180 gr bullet,so could feel like a 7mm mag at the bench.But my old favorite 300 Win Mag was a long throated job on a magnum pre 64 M70,Brown stock and 24" Krieger....with bullets seated out, it gave 3150 with the 180,acted and kicked like a 300 Weatherby. My 7 Rem Mag was housed in a lighter rifle and was much easier to shoot.
Best way to look at it I think,is compare them at equivalent velocities with roughly comparable bullets......start a 160 gr bullet from a 7 Mashburn or Weatherby at 3200 fps; it takes powder charges in the mid 70's to do this.Then try to start a 180 gr 30 cal bullet at the same velocities(a 300 Win Mag is not generally capable of this but a 300 Weatherby is)in a 300 Weatherby,and powder charges jump substantially into the mid 80's.
That's about 10 gr more powder and 20 gr more bullet at the same velocity.We shoot a pair of 7mm Mashburns and a 300 Weatherby,all loaded as stated above, side by side frequently; both Mashburns are lighter rifles and my pal and I both agree the Mashburn rocks a good deal less than the 300 WCeatherby,even with 175 gr bullets over 3000 fps.Plus there is no way we could build a 300 Weatherby as light as the Mashburn without getting kicked a lot harder as well.
Shoot a 300 Win Mag with 180's at 3050;and a 7 Rem Mag with 160's at 3050.....your powder charges will be a bit heavier in the 300,and the recoil will be greater for the 300 in the same weight rifle.
So, for roughly equivalent ballistic performance the 7mm's will rock you less,and this is what many of us mean when we say the 7mm's recoil less
for a given level of ballistic performance but I never said they were gentle
