Time to get out the 80 pound pot and start weighing lead ingots on the triple beam balance. Thinking about it, maybe I'll stop at enough bars of tin for 3 pounds plus or minus and enough lead to match the tin for 1 to 20. 60 odd pounds of alloy ingots should fill up the space in my lead box and last through this year's Cowboy Silhouette matches assuming we have them.

Not every thread opens with a question. Some of us can have a discussion with just an opening remark. 
Oneatatime, I don't usually measure my alloy to the smallest increment either. I have found little difference in the mixes as long as I can say without any attempt to lie to myself that it is 'close enough'.
I have asked several times whether anybody really can tell if his latest batch of lead is 19 to 1, 20:1, or 21parts to one part. So far no answers, so far as I can tell they cant's say either. Have fun mixing up yer newest ticket to fun.

I can't help it. I got started as the lab assistant in chemistry class and I mix my own chemicals for photography where it does matter. Tonight I had the triple beam set up with the kilo and half kilo pre weights and I grabbed the kitchen digital that is iffy at larger weights. Then I put 4 muffins, or 4 koalas(?), or 4 large cornbreads on the kitchen and took what it said and set the triple for the nearest 10 grams less and transferred the lead over. I'll admit I then bumped up the 1/10 gram scale to the nearest gram as the balance swung and called it good. I'm within a couple of kilos now so will switch to small cornbreads to get close enough for government work. I can say that, I worked for the government;-) By the way, one of the two nmoulds I was casting with today that I used up all my alloy on was an old Lyman small block single cavity 412163 with old highly ergonomic small tapered handles. It sure is a pleasure to cast with that combination.

80#'er.... WOW!  I was getting a little puffed up because I just finished a 50#'er modeled after Dave's two piece made from some 6 and 8" pipe....  When you cast bullets that go ten to a pound the smaller pots don't go very far 
Have fun !
Ps- I sort mine to 20 lead and 1 tin unless I lose count....

Greg

Charle, here are the muffins, koalas, large cornbreads and small cornbreads. Looking at the koalas now I guess they are more like "hello kittys" but koalas are cuter and I figured they would make (drum roll, please) koalaty ingots so I'm staying with that. GT, here's the big pot set up with my 63 pounds of lead ingots ready to melt. It's a heavy duty turkey fryer (I can stand on it and jump up and down - have to if it is hot). The pot is a 14 inch Dutch oven and as you can see it will hold well over 100 pounds. From the high tide marks inside I must have had 120-150 pounds in it when I was pouring lead ingots and that was like half full. I added the skirt to it for efficiency's sake. Now I have a nice pile of 20 to 1 Lyman ingots in the lead box so I'm back in business. Why 20 to 1? It casts great and an extensive test I did once at 300 yards showed that 25 to 1 shot much better than 30 to 1 and 20 to 1 shot better than 25 to 1. YMMV

My molds for ingots are just the round muffin tins. When filled level each round will weigh right at 2 lbs. I've never cared what they weighed really, just that I used a certain number to 1 round of tin. So my batch size varied depending on what ratio my mix was for that pot.

I read some where Pope said 15:1 was best, but it would be so hard to BS I never went there.  I probably tried it 25 years ago and didn't see any difference.  Takes quite a bit of pressure to BS a ML style Pope.   Memory is too foggy 

I am not sure if I should put my hat in the ring on this one but here goes.  I try to use only the best scrap I can find. Old lead flashing or old lead water pipe. Nothing else. I have found that scrap lead usually have some antimony in it and can make your alloy much harder than you think it is. 

I weigh my lead flashing and melt it.  Weight the dross and add additional lead. Usually if your lead weighs 25 lbs you have a pound or three of dross depending on how clean the flashing was.  So for 25 lbs of lead I will add 1 pound of tin. This keeps it simple for me. My ingots for casting weight about 1.5 pounds apiece.

I usually make 4 batches like this and number the batches 1,2,3, and 4. When casting bullets I use the ingots in rotation to blend any error in the batches.   

If I did my part the Saeco tester for 25-1 reads 4. I admit sometimes even when doing everything right I end up with a little harder alloy. This has led me to believe that it might be a good idea to use a little less tin than called for. I am sure that flashing has impurities that will only make your mix harder. In addition bullets made from scrap will age harden due to the antimony. 

Obviously you can avoid all the problems by buying certified materials.  Like others have said I have shot 23-1 that was suppose to be 25-1. Shot well but if your trying to control diameter, weight and consistency it is not helpful.