Hey Robert,
I have used recycled lead from different sources. Shotgun pellets being on of those sources. At that time I was shooting mostly cast bullets in Handguns and no rifle loads. It worked fine with nothing added. A little dirt comes to the top and it is not a problem.
I have used a sifter with 1/4" screen to sift out semi-wadcutter bullets and jacketed bullets. Most of the grime breaks loose while sifting from the sand. I started to pick out the jacketed bullets and determined that was nonsence and I just threw everything in the the big pot, melted it and cast it into ingots. With this type of lead with 2% tin added to the melt, I have shot 25 caliber rifle bullets up to 2245 fps with no leading or other problems.
I have used tons of wheelweights that are messy with grease, rubber parts and other debri in the bucket. I add 2 % tin and we are off and running with rifle bullets. Currently, I'm adding 1 pound of Linotype to 3 pounds of wheelweights and it is working fine. However, I'm going to try the 2% tin on my next cast. The tin helps fill out on the sharp edges in the mold.
I have loaded and fired 3,440 cast bullets in rifle cartridges this year so far. As far as lead goes, if it melts, I cast it. Sometimes, I mix lino or tin and sometimes I don't, depending on how the bullets look.
Never turn down a source of free lead. I know there are folks that will disagree with me when I say Lead is Lead with slight differences. If you have a batch in a mix, keep the bullets in a separate container and shoot them all together. Do not mix you bullets from different lead and you will do just fine.
About one third of my shooting each year is cast bullets and I'm trying to make it more.
Harold Clark