No, .303 bullets are typically .312 inch (7.9 mm) diameter while 30-40 Krag bullets are typically .308 inch (7.8mm) diameter. Typical common bullet weight is very close, 174 grain for .303 and 180 grain fir the 30-40. Coincidentally the shell rim is about the same size, so you use the same reloading shell-holder. That should at least save you $2 to $10 at least.
Most likely, you'll use American Boxer primed brass. In that case, both will use large rifle primers. As to powder, you HAVE to consult a good reloading manual. I use IMR-4064 for .303. Its a nice slow burning powder. I don't see any reason that you won't find loads for that or another similar powder for the 30-40.
Don't even think about trying to reload foreign Berdan primed brass for the .303. Its not worth the serious pain in the ass it is.
I reload both. I use Remington 9 1/2 standard large rifle primers. (they're MilSpec) snd either IMR or Hodgdon 4895. 4064, 4320, and even 3031 will give very good results with either of these calibers.
BTW, I've had far better luck with round nose bullets in the Krag.
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