COWW at $1 a pound will do most anything you want. The small amount of tin just makes the alloy a bit better and easier to work with. Roll of lead free solder pull off a foot and add to the pot. Maybe two foot. Some will be good, a bit more will be better. Any greater percentage of tin than the 2 or 3 percent antimony is just wasted.
I make home mixed Lyman #2 for use in 8mm Mauser or 303 British as alloys go it is nice to cast with and makes a good rifle bullet for those uses. Not required to use that rich of an alloy but it will certainly give good results. Another option is buy some COWW at $1 a pound in S&S forum then pick up some Lyman #2 at Rotometals. Mix the two in equal amounts to make a small 50/50 batch. Cast with it and if it works ok then you have the option to save money by using the inexpensive COWW's to cut the expense of the Lyman #2 in half. Pretty sure you can run a good load for punching paper at 50 to 100 yards using that 50/50 or plain COWW's + 2% tin from solder. Equally sure you will be good with straight Lyman #2 alloy from Rotometals.
Main thing is to start so you can make specific mistakes. Then you can post question about why is this specific thing happening. Get some suggestions, then re-melt the mistakes and try the suggestions. Can't make progress until you begin. Like learning to ski, just plan on doing some face plants and start down the hill.