777 and pyrodex are used by volume as per black powder. Mark a vile where 21 grns {or whatever load you want of black powder comes to and then fill to the same leval with the substitute. weigh this load and theres your load by weight. Iv tried both substitutes and got to be honest when i say no one at our club who has a black powder licence shoots a substitute. However, both 777 and pyrodex worked well with plenty of umph, smoke etc. Accuracy was no different to b/p. As per most things when shooting on the dark side it comes down to personal choice and what works for you and your gun. Tim