I have a navy arms 50-70 and want to cast bullets for it..My question is what alloy should I use for it? Would I go so called pure lead or maybe something like 20 to 1 lead tin..Do you think that wheel weights will make a good bullet as well?

bulletmaker,
In my experience, w.w. with 1% to 2% tin added will work just as well as 20/1.

Have fun,
John

2 to 5 percent tin to lead,is just fine for that caliber.That is what I feed my 45/70 rifles.However,adding that amount to wheel wheights is good,also.
Tin,in excess of 3 percent,is mainly for easier casting.
Frank

So your saying that I can use like 19 lbs of WW's and add 1 Lb of tin to it?

A tradtional alloy 19 pounds of LEAD and one pound of tin. Wheel weights are a bit hard, but some 50-70's will shoot them....a lot depends on the size of the as-cast bullets and the real diameter of the bore.

I got WW to shoot pretty well in an original Rolling Block (actually, considering where you are from, you'd have liked that old New York contract rifle), but had to find a mold that would cast them a bit large. they'd shoot well (about the same group average) as the lead/tin bullets out to 100yards...farther than that, and the lead-tin bullet's accuracy edge really started to show itself.

Best accuracy was from the lead-tin alloy. Almost as good is a 50-50 mix of wheel weights and pure lead, with a bit of tin added (usually in the form of bar soldier).

Rifling was excellet for its age, but a bit rough compared to a modern rifle, and was 36" long. Hard to get enough lube on a bullet to last through a 36" long trip, so stick to the best you can buy. The hard wheel weight bullets would leave some lead fouling, oddly the soft bullets seldom did.
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Tin isn't really that great for hardening...it does harden some, but what it does best seems to be to reduce the surface tension of molten lead; makes it flow more easily so it fills the mold out nicely.

Interesting indeed-very interesting

According to the Lyman casting book, 9# OF WW with 1# of 50/50 solder added will give you the equivalent of Lyman #2 alloy at 15 BHN. I add 8 ounces of 95/5 solder to 10# WW for about the same outcome, which is actually the same as the 19# WW and 1 Pound of tin you mentioned. The 95/5 solder does add a smidgen of antimony though.

BULLETMAKER w/w work just fine but 1/20or 1/30 mix in the black powder world is what your looking for,soft bullet so it will bump up! (seal the bore) in casting, proper size
to bore and keep your alloy soft as possible without leading and that can be determined
by psi. NOW lubes for black powder you don't want anything with petroleum base lubes but non petro lubes work on smokeless loads up to a point. Then gas checks !

Bulletmaker,
use whatever mix doesn't lead the barrel. Experiment, experiment, experiment. I've found lots of guns work perfectly with w/w and others lead up if you walk by them with a w/w bullet in your pocket. Play around until you find what's best for your gun.