SN is tin, the number after it is probably the ration of the lead to tin. 1 or 2 parts per volume.
What you don't know is the hardness of the alloy.
Can you mark it with your thumb nail? Hard vs Soft.
Yes, it is all good for making bullets, shiny vs dull. May have to adjust your alloy though.
You may have to buy a lead hardness tester to find out what someone gave you, or you could ask them.
12-16 Brinell is good for softer bullets at lower velocities, but some claim that they use 12 Brinell for magnum loads.
You are on a reloading forum, do you reload?
If you don't there is no point in keeping the lead unless you want to make fishing sinkers out of it.
You can get into casting fairly cheap to see if it's something you want to pursue.
As far as whether or not it's for you? We can't answer that. I cast some and I do enjoy it when I cast but like reloading, it can get expensive in a hurry if your aren't practical about it.
I use a Lee lead melting pot,
https://www.tacklewarehouse.com/Do-...Ja8tXE_39Nm-Q1_1dTzuxCZjaaVb4ePhoCZw8QAvD_BwE
and Lee molds, the molds do work for all the more they cost.
I have several of them. But chances are if you really like casting you will want to move on to a more expensive, higher capacity furnace and cast or brass bullet molds. This is where the money comes in, but that's part of a fun hobby.
Now, If some one gave me 200 lb of lead I would be ecstatic.
I would be figuring out how many bullets I can make out of this lead before I even cast one.