The weight versus volume debate has raged for a century.
Scientifically, black powder should be measured by weight. Volume is a terribly inaccurate measurement for determining the amount of a reactant in a chemical reaction (such as combustion) unless it's a liquid. However black powder was traditionally measured by volume because it was a lot faster and easier. Substitutes are designed to be measured by equivalent volume so unless you can find the density difference between it and black powder you kind of have to use volume. For true black powder I always measure by weight now and find it got rid of most of my flyers. There was one article I read online where the author found as many different volumetric measures as he could and found the average charge they weighed using different granulation's of different brands of black powder and substitutes. The results were all over the place even for the true black powders depending on brand and type (FFg versus FFFg). Velocities (in a muzzle loader) were likewise all over the map. Volumes that contained more powder (by weight) shot higher velocities. Exactly as the scientific method would predict.
A big reason black powder can be measured by volume is because it is so forgiving because it has such low chemical potential energy. If you loaded Varget and were off by 5% (say 2.5gr in a 50gr charge), you could have wildly different velocities. This is because the chemical potential energy is so high so those 2.5gr contain a good deal more energy. With black powder the energy potential is so much lower you can be off by quite a bit and only have slight velocity variations. It's the same with ultra low density powders like Trail Boss. I always measure Trail Boss with Lee scoops and can still shoot decent groups. If you want true precision though, measuring black powder by weight is far more accurate.
And now I totally expect to get flamed by people who have "always done it by volume" who will tell me I am utterly wrong.
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I recently switched to smokeless lube and 3Fg instead of SPG black powder lube and 2Fg. Found my rifle (an H&R Buffalo Classic) shoots better groups now. I read about it on the Cast Boolits forums. Using this method you need to clean the bore between each shot but other than that there is nothing different. There is no buildup of tar/junk and no leading. The buildup of difficult-to-clean tar like stuff from using smokeless lube with black powder is a result of firing many rounds. Black powder lube keeps the fouling soft after multiple shots so it remains easy to clean. I have fired up to 5 shots in a row without cleaning using this method just to test and the fouling remained easy to clean. The accuracy went to hell after the second shot though.
With 2Fg I was hard pressed to get much more than 60-62gr of powder in a 45-70 case. I don't have a powder compression die so if I try to compress the powder with the bullet it bulges and sometimes wont chamber. With 3Fg I can much more easily fit 70gr in a case and have even gotten as much as 75gr with smaller 340gr bullets. I haven't chronied those ones but they kick substantially less than level 2 lever loads with smokeless powder. Brass and primers are identical to those fired with 60gr of 2Fg (not that you can trust any of these pressure signs at black powder pressures).
For over powder wads and cushion wads (for use with reduced charges since you need to fill the case to compress the powder) I order from Track of the Wolf in the US. That's just for round-ball loads though. For normal loads with bullets I only use over powder wads.
Anyone have some 45-70 brass to sell?
Budget Shooter Supply has Starline brass in stock.
http://www.budgetshootersupply.ca/frame.cfm?ItemID=1401&CategoryID=56
http://www.budgetshootersupply.ca/frame.cfm?ItemID=194&CategoryID=56
The Bullet Barn also has Starline brass listed as in stock but at higher prices. $40/50 and $75/100. Also not a site sponsor so posting links is frowned upon.
Starline is what I use for a lot of my loads both black powder and smokeless. Also use a lot of it for 44 magnum.