"Frosted" bullets are usually signs of a too hot lead mixture, or too hot mould. Wrinkled bullets are usually too cold mould.
With rare exceptions, there is no such thing as a "too hot" alloy. Anyone who shoots in, or visits, any of the Cast Bullet Association benchrest matches will see that many of the top competitors are shooting bullets with a frosted appearance. We're talking about bullet casters who are shooting 200 yard groups that measure in the area of .5". Hotter alloys generally give better fillout, particularly if you pour a generous sprue for the mould to pull from as the bullet cools.
Obviously, especially with some heat sources, you can take alloy temperatures much too high. It is pretty much impossible to do that with a commercial bullet casting pot, however.
Lead alloy mixtures are used for various types of shooting. Pure lead or low alloy lead is used for Black Powder firearms. You want the bullet to expand fast to seal and fill the rifling grooves. Medium hard cast bullets are used for game, because you want a bit of expansion, but also want the bullet to hold together and penetrate. Hard cast bullets can by used for target shooting.
There is no real relationship between hardness and use. There is a relationship between hardness and the load the shooter chooses.
Proper hardness is directly related to the tensile strength of the alloy versus the working pressure of the load it is being fired with. Competitive shooters use everything from simple lead/tin alloys to linotype or monotype - a variance in about 25 points on the Brinell scale. I've posted charts here at CGN a number of times which lay out the harness for best results throughout the range of normal operating pressures, but that is getting a bit complicated for someone just starting out in my opinion. If you stick with pure lead or 1/20 - 1/30 tin/lead alloys for black powder and wheelweights for smokeless to start out with, you can't go too far wrong when you're starting out.
You can vary your lead mixture by adding certain metals to alloy the mixture. Lead is hardened with the addition of Tin. Antimony can also be used.
Tin has, at best, a minor effect on bullet hardness. The benefit of tin is that it reduces the surface tension of the molten alloy and increases ductility. The result is it enhances bullet fill-out within the mould - fewer voids and partially filled lube grooves, etc. For those wishing to confirm this, use an LBT Hardness Tester or similar instrument and compare hardnesses. You will find pure lead scores about 6 BHN and 5% Tin will get you all of about 10 BHN. Significantly increasing bullet hardness is achieved by adding antimony. Just 3 - 4% Antimony will get you in the area of 10 - 13 BHN (very few of us start out our alloys with all pure metals, so figures are rather inexact). Furthermore, while lead/tin alloys can not be heat treated to increase hardness, heat treating of lead/antimony can be used to select specific hardnesses up to as high as BHN 30 - and beyond. I've never gotten any harder than BHN 30, but I've never tried as I never have had a need for something harder.
Heat treating wheel weight alloy is both controllable and predictable ie: It is possible to heat treat wheel weight bullets and predict the final hardness to be achieved. Hardness does not increase until the quench temp (after a ½ hr heat soak) reaches 420 deg. F. as measured with a digital thermometer shaded from any direct radiant heat.
Temperature vs. Resulting Hardness
410 12 BHN
420 15 BHN
430 17 BHN
440 23 BHN
450 29 BHN
Exceeding 450 does not cause any significant increase in hardness.
460 is too close to the plastic deformation stage of wheelweights and you're on the ragged edge of your bullets slumping.
Generally revolvers use about 1 part tin to 40 parts lead, Automatic pistols use a 1-10 mixture, Rifles with plain base bullets a 1-15 mixture, and Rifles with gas checked bullets a 1-10 mixture.
A 40/1 lead-tin alloy has a BHN of approximately 8. The tensile strength of lead alloys is BHN x 480 i.e. 3840. Bullet obduration and resistance to stripping is usually at pressures falling between 3 and 4 times the tensile strength of the alloy. So we're talking 11,520 psi to 15,363 psi. There are MANY revolver loads out there that well exceed 15363 psi - consider the SAAMI pressure standards for the .357 Magnum, 44 Magnum, etc and so forth. The SAAMI pressure limit for the century-old .38 Spl is 17,000 psi... A 40/1 lead/tin alloy is going to fail miserably in anything other than mild target loads.
It doesn't matter what the bullet is being used in. What does matter is matching the bullet hardness to the operating pressure of the alloy being used. That, and getting a proper bullet fit to the leade/ball seat of the firearm.
One important thing to remember is that a lot of wheel weights have been melted down for cast bullets. They are fairly hard, usually about 93% lead and 6% Antimony plus other metals....you have to add Tin to make them softer if you use them for hunting. They make fair target bullets FOR HIGH POWER, GAS CHECKED BULLETS
Adding tin does not significantly harden alloys, nor does adding tin make alloys softer. And most of all, it can't harden alloys on the one hand and then soften them on the other.
Wheelweights commonly test at BHN 12-13, meaning that as-cast, they are good for loads with chamber pressures up to around 23,000 psi. That makes them a bit mild for the pressures most casters will be looking for in a hunting bullet. Assuming most hunting loads are going to give you a chamber pressure between about 31,000 and 42,000 psi, you will need a BHN of around 22. You can either get that from using linotype or from heat treating wheelweight bullets at 440 degrees for about half an hour before quenching.
This will match the pressures of a .308 Winchester load firing a 170gr. cast bullet at about 2100 fps - or a .45/70 firing a 425 gr. bullet at around 2000 fps. You can see why the old timers who had nothing but cast bullets favoured big bores...
Bottom line: yet again, for best results it is best to match bullet hardness to the operating pressures of the loads you have in mind.
As far as accuracy goes, J. Francis Rabbeth fired 15 rounds into less than TWO INCHES at TWO HUNDERD YARDS, in 1891. That is over 100 years ago.
The CBA record for the plain base bullet class is 1.063" for a ten shot group at 200 yards; the Heavy Rifle 10 shot group record is .772". We've relearned much of what we forgot from the old boys and are moving forward.
On the other hand, with the growing initiatives to eliminate wheelweights made of lead alloys, we may either be buying babbit for our casting - at considerably greater cost - or ramping up the alternative of focusing on paper patched bullets.
For casters really wanting to get some expertise on cast bullet issues, a membership in the Cast Bullet Association is well worthwhile. The Fouling Shot is an excellent magazine for technical information. On the other hand, you don't need to join to use the CBA email list or online forum. With the expertise of resident metallurgists like Bill Ferguson (The Antimony Man) and people like C. Ed Harris answering questions, there's not a lot of questions you can come up with that these folks can't steer you straight on.
Some links:
http://www.castbulletassoc.org/index.shtml
http://www.castbulletassoc.org/forum/
http://groups.yahoo.com/group/CB-L/
I'm all for you making your own bullets, but you need a source of fresh air when using lead shot. Some of it contains arsenic, not something you want to be breathing indoors. Cast bullets outside or in a very well ventilated area.
Unless you're messing around with mystery alloys - something I personally stay away from - or nasty stuff like used battery cores and similar very bad ideas, inhalation is not a likely source of problems. I'm certainly not discouraging good ventilation, but normal alloys don't gas lead, arsenic, etc at casting temperatures. I've been casting indoors, in a not particularly well ventilated room, for decades. I ask my doc to test for poisoning every year with my annual blood test - not because of ventilation concerns, but because of the much greater risk from ingestion. Most people who end up poisoning themselves dealing with lead alloys do so through ingestion. So far, I've had completely normal results every year - including way back when I worked as a blaster in a mine whose primary product was galena aka lead. I pay a lot of attention to keeping my hands clean and not putting anything near my mouth near a casting bench - no drinks, no food, etc.
In particular, probably the most poisonous stuff you will find around your casting area is the dross you skim off your melt. The oxides in that are downright nasty, and I take particular care in how I handle and dispose of dross.
If you do choose to cast outside, be aware of the consequences of a raindrop or bug ending up in your molten alloy... if that happens it will immediately become one of the most exciting moments in your life.