I don't use or have the need for any tin. Fillout is good with controlling the mold temperature and not allowing overheating. I've been cutting my WW's with Pb 50/50. I sort all the WW's and keep the soft stick-ons seperate, treating them as pure lead. An alloy of 50% WW's and 50% Pb cuts the antimony to 1 1/2 to 2%. In an AC state the bullets are 9-10 Bhn. The alloy has enough antimony and arsenic left to still harden. Either WD or OHT bullets run 18-22 Bhn. It's also malleable enough, even heat treated, to expand some without riveting. The mushroom or petals will still sometimes shear off, but they're pretty good sized.
I just ran some wet newspaper expansion tests using a 300 gr HP out of my 375 H&H. The media was at 50 yards and my MZ velocity was approx. 2,400 fps. Penetration was 21 inches deep. The first 8 inches of wound cavity was 3 inches in diameter. The mushroom fragged off into the second grocery bag of wet paper. Evidentily this bag was a little on the dry side where the bullets went through. Retained weight was only 100 grains. Some of this is due to the HP cavity depth which I'm going to shorten up some. The test rounds cavity depth was approx. 0.400 inches deep.
Another plus for this alloy is it eliminates the grey antimonial wash you get in the barrel at high velocity. I began to notice this when I started getting above 2,000 fps with straight OHTWW's. The lube wasn't giving up (LBT Blue), and I wasn't getting leading in the traditional sense. Just a powdery grey coating. I've compared a 50/50 alloy against straight WW's, both soft and hard, and the 50/50 wins most every time in the accuracy dept. I pretty much shoot this in all my guns, whether handgun or rifle.