[Visionz45]

Can I use .303 British data as a basis to work up for my 7.7 Jap? Ive loaded for the 7.7 quite a bit now and find my data to track more with .303 data rather than what little 7.7 data there is available.

[NCsmitty]

IMO, that would not be a wise decision, as a quick scan of Hodgdon's online data for both shows some loads are close and some are not.
Just garner proven loads for the 7.7 where you can and compile them for future use. Look on ebay or other auction sites for manuals to add to the collection. You won't regret it.




NCsmitty

[Curator]

The case capacity of the two are very similar. Since the Type 99 rifle action is considerably stronger then the Lee Enfield, I would not worry about using .303 British data for 7.7Jap cartridges, but not the reverse. My experience shows a load (42 grains of Rx15 and Sierra 174HPBT) that clocks 2440fps in the .303 only gives 2200fps when shot in one of my type 99s even though the barrel length are within 1/2 inch of each other.