kozak6 beat me to the article on box 'o truth
Basicly the dimes are gonna cost quite a bit.. that's assuming at that moment cost was a concern.
If you wanted to make some up you could try flat washers for cheaper.
they're not particularly powerful.. and surely not like a slug, They will separate in the wind, maybe if they was epoxied or something
they will be lighter then the heavier LEAD shot I do know that if you have to light of a load you won't get the velocity you need.. so you can't just willy nilly swap load weights or think lighter load is going to make it super fast or something.. apparently it's something to do with compression of the load..
Powder / Payload Weight ratio.. sorry maybe not the correct technical term but you know what I mean.
If you've not heard of wax slugs check them out, all you need is candle wax, heat source and the original birdshot.
The wax binds the lead till it hits the target and is actually QUITE devastating.
Kinda like frangible shotgun rounds.
There is a down side though.. candle / parafin wax has a low melt point so these are not a thermally stable round, so a warm gun might have too hot a chamber and make a mess after a while, also storing in the car for example would probably turn to goo.
Try youtube there are many video's on making these rounds, iraq veteran has quite a few I know.
You most certainly would have access to candle wax in the old west.
Another option is the cut shell, these generally will not feed out of anything other then a break action.
all you needs is a knife you cut the shell just under the shotcup, but not all the way thru.
The idea here is the top half of the shell will separate and leave as one solid chunk of plastic/lead creating a slug like effect.
out of the two the wax slugs look the most effect imo.
another thing you might consider, I currently do not reload, I do want to in the future, but I also want to get into casting.
Probably my first step into casting will be to take cheaper birdshot value packs and then melt and cast into larger shot.. #4 buck, #00buck, and also lee key-drive slugs, which are designed specifically for this task and will fit in shotcups and take a fold crimp rather than traditional roll crimp for slugs.
I've seen youtube videos that show the 7/8oz slugs work best (1oz seems to tumble a bit).
Since you're already starting with "good" lead quality should be a simple melt/mold situation.. no real prep or purification needed.