I don't load for .32-20, but I do use a .32-20 case as my 21 grain measure!
The accepted way to load BP, at least for rifles, is to use a drop tube. I use a 24" piece of copper pipe mounted on a stand knocked together from a coupla pieces of 2 by 4. Some use an aluminum arrow shaft. A long metal supply tube from the plumbing display at your local "Lumbarama" store looks promising. With a 1/2" pipe, I slip a reducing fitting on the bottom and stick a funnel in the top.
Measure by volume, but check-weigh on your scale to make sure you are on track. That 20 grains sounds about right, dropped, and about 1/16th" to 1/8th" of further compression when seating the bullet. Some use a "compression die" but if used too enthusiastically the grains at the top of the load get crushed. Some also recommend a card wad over the powder, but unless you are trying to knock over a sillouette at 500 to 1,000 yards I think it is only an option.
Cruise the boards as there is a lot of advice on loading BP available. Lyman puts out a very good BP loading manual.
Hint; A .40 S&W case drops 18.5 gr. poured in from a can spout or dipped, levelled in both cases. (you better weigh it yourself - Boy!)
I figured out a neat trick for loading BP cartridges that use a 3 die set. I resize, use a Lee expander die on the mouth of the case, throw enough powder to come to the mouth of the case, and have the expander die set to compress the powder to the correct depth for the bullet I'm using. Then I just seat the bullet and crimp with the seater die. The Lee die works on every case, so I just adjust it for whatever I'm loading at the time. This technique works well with the 32-20, but the problem with it is it's hard to find a bullet with big enough grease grooves to allow you to shoot many rounds in a rifle without cleaning. In a revolver it's no problem.
I know one reason that the newer brass will only hold 21 grains of powder up to the top of the brass, it is solid headed brass. I have some old balloon head brass for the 32-20 that will hold 25 grains of 3fg powder to the top of the case, put only 20 in it and I have plenty of room to seat a 115 grain bullet. As for grease grooves, there is an old lyman design that has a very large grease groove in it, that should work well with black powder, but you will have to watch the auction sites for one as it is out of production.
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