No, no, no! .303 British is a higher pressure round and with a stronger action. See the maximum pressures. Krag is 40,000 CUP/47,000 psi and .303 is 45,000 CUP/52,000 psi. Please don't use .303 British data in your .30-40 Krag!/QUOTE]
Please point out where I said to use 303 loading data for the 30-40. Likewise, 7.62X54R may be a close ballistic match for 308 Win or even .30-06, but that doesn't mean loads data are interchangeable and that applies to lots of cartridges if grouped by performance!
Also if you trouble to read the original post, the question is about factory .30-40 ammunition. (I though SD is a deerstalking forum!) ..... NOT FMJ rifle or machinegun or any other loads developed for and used by military forces.
Whatever loadings the 303 once received for British military use, I'll stick by my assertion that factory 180gn SP ammunition was loaded to near identical levels by US ammunition companies, COTW and Forker quoting it (.303) as 2,460 fps or all of 30 fps more than the 'nominal' 30-40 value. Although I've never chronographed Winchester 303 ammo that was once widely available here myself, I've read several times that actual MVs fail to achieve the listed levels by a substantial margin. In the days when Norma loaded the 303, its ammunition was likely somewhat 'hotter' though.
As to the two cartridges being dimensionally similar, I suggest you refer to Ken Bird's 'Pet Loads' and his two articles for Handloader magazine on loading the 303 British where he both comments on the similarities (hardly surprising as the US Army copied the existing British design with minimal changes to get a 'smallbore' cartridge in service quickly) and recommends using 30-40 brass in the British rifles. This was partly because 30-40 was more easily found in the US at the time, but also because its brass was regarded as stronger and better matching 303 chambers better too, and gave a longer life.
Finally, you seem to assume that Bearstalker must be using a weak US M1892-99 series single lug 'Krag' based rifle. Whilst this is likely, it is certainly not inevitable and a much stronger action may be in the intended recipient - the P'14 has been used many times as the basis of .30-40 sporting rifles, a shot-out 0.312" groove barrel replaced by a 0.308" groove dia. equivalent with the benefit to North American users of much better availabality of .30-cal sporting bullets.