correct me if i am wrong...N140 is single based (no nitroglycerin) and therefore less harmful to barrels, while N540 is double based containing nitroglycerin. berger's book has a great burn rate chart seeming to have the best rates i've seen...some have BL-C(2) burn rate very close to varget. i love vihtavouri powders but for two things...cost and they seem to be temp sensitive, while varget is not.