Gentlemen,

I developed loads and shot a standard .378 Weatherby (Japan production).

If you start at the minimum loads, you might get .375 H&H ballistics and recoil, so this is not a problem.
The factory loads (270 soft point and 300 soft point) are ugly to shoot (at least for me).
As written before from the NE members, the recoil is very fast!

BUT does not hurt with the correct clothing and a thick recoil pad.

My rifle was equipped with open sights only and without muzzle break, which is reported to be very good in recoil reduction.

I would recommend to buy this Hartmann & Weiss if you can tolerate 375 H&H recoil (with reduced loads in the 378 case) and load it up if you need :-).

best regards
Rolf

PS: I have to admit that I would buy nearly every rifle from Hartmann&Weiss due to the quality, so the given caliber would not be dominant in the "BUY"-decision...