All good questions.
The alloy MUST be very ductile. This dictates pure lead and tin lead only for bullets which must penetrate well. Since the harder tin lead alloys age soften rapidly, mixes richer than 1/20 will have to be used within a couple of weeks after casting if they are loaded to full potential, or to the point where leading begins to be a problem. In other words, if a load is developed which is on the thresh hold of leading and some of the hardness is lost, severe leading and inaccuracy will ruin the loads. So I recommed 1/20 tin lead alloy only, and live with whatever speed is possible with that hardness. Keep in mind that the best lubrication possible is mandatory to get good speed, and the best is one of the LBT bullet lubricants.
For varmints, where good straight and deep penetration isn't a factor, use antimonial alloys and the wings will break off soon as the bullets open up. Hardened ww alloy is fine, or aircooled. The wings will break off with either.
If you are using a mold that is undersize, use heavy duty kitchen foil and you'll increase diameter of the bullet nose by .002. If it is of proper size, use standard duty foil, which is .001 thick and won't open the mold as much, but will be a little easier to handle the little pieces while inserting in the mold.
Depth to insert is up to the user, type of gun, velocity etc. If the foil is inserted too deep, the long petals will open up with cyntrifugal force before the bullets reach your target. For safety sake, experiment to find the depth where petals open in flight at the speed you'll be shooting, then back the foil depth up by a good amount so you are far from problems. The foil doens't have to be deep. One caliber deep is adaquate and probably best, while even less is fine for the slimmer rifle calibers. It works well for all calibers, so I'm speaking broadly here.
Easiest way to insert the foil strips is to cut them so the alignment pins don't interfere and a bit wider then mandatory. Lay each strip on the mold, to a line drawn at the desired depth (use fine felt pen), then fold the excess down so the pieces are L shaped. These can be dropped quickly on the hot mold if you turn it partly upside down. If the foil slips a little while closing the mold you'll see the bent leg standing out from the mold and can fix it without wasting the bullets.
My recommendations is that they be used for varmints only with handguns and for game up to deer with most rifles throwing bullets of 150 grains and up. For big game, it is best to keep the petals short, because the 'mushroom' will hold together better, and penetrate deeper than with long petals.
