Ive shot thousands in a webley mark iv. Used both lee 158 semi wadcutters and 158 rn. I used fairly soft bullets approx lyman #2 alloy and usually 3.5 gr of higgensons sp 83 , 0r 3.8 gr of unique which gave 750 fps. these were accurate . These loads are fairly stiff and i believe they bumped up the bullets nicely. The same loads gave sticky extraction in aS&W victory model so i backed it off to 2.8 grains which was accurate in the S&W but no good in the Webley. I never slugged the bores but I would suspect that S&W just used standard .357 barrels In these revolvers as a wartime expediant