I have a 375Flanged Mag double, a spare set of barrels made in the 1950’s by H&H for my pre-war(1) 500/450 3 1/4”.

Regulates around 2400fps with the Woodleigh 300gr SN RN. Very mild to shoot, the extra weight of larger frame of course, it fits too!

My 375 Belted Mag magazine Rifles are around 2600fps.