While H4350 and IMR4350 are reasonably close, your "supplier" is an idiot for suggesting the H4318 and IMR4381 are the same. From the 2007 Hodgdon's manual for the .270 WCF and 130-grain bullets:
60.0 - H4831 - 3019 fps - 51,000 cup
55.8 - IMR4831 - 3002 fps - 50,100 cup
If you used H4831 max data for IMR4831 you would be 4.2 grains over max - that would wake you up. If you used IMR4831 max data for the H4831 powder you'd be almost 200 fps slow - that would pi$$ you off.
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