So, today I decided to get into casting my own bullets. Bought the melter, a die, and a roll of solder (95% tin). Melted down a few old dive weights, mixed in some of the tin solder, and had a merry old time. I made up a couple of hundred rounds. I measured them, and they came out at .312".......the box for the mold said .309 ......ok.....now
My first comment should have been "Join the Cast Bullet Association". It's cheap, and there's an overwhelming base of genuinely expert knowledge there, from people like C. Ed Harris to Bill Ferguson (one of the resident metallurgists and purveyor of fine alloys and casting tools), to custom mould makers and cast bullet gunsmiths and competitors. You'll find them here:
http://www.castbulletassoc.org/
Their cast bullet forum:
http://www.castbulletassoc.org/forum/
And their unofficial email discussion site here:
http://groups.yahoo.com/group/CB-L/
I long ago decided that people who have figured out how to get .5 MOA ten shot groups with cast bullets are probably well worth listening to. Well, it has certainly worked well for me since joining nearly two decades ago...
Regarding your original post, whole bunch of things here.
First, you don't mention the make and model number of the mould you're using. However, it sounds like it is seriously oversize - or the two faces of the mould halves aren't fully closing - if you are getting +.003". Generally speaking, most factory moulds are cut to give their finished diameter using Lyman #2 alloy or something very similar - like wheelweight for example. If I remember correctly, the diameter difference in a typical .30 caliber mould between Lyman #2 and WW is something like .0005" - nowhere near three thou.
I would be inclined to take an oversize mould back for exchange - but not before I had slugged the leade/ball seat to find out what it measured. You just might find .312" to be just right, and that would simply require some adjustments elsewhere.
I size to .0005" smaller than the ball seat measurement. That is a bit of icing on the cake that most people wouldn't bother with, but send your die and requested measurement to Robert Stillwell and he will do that for you cheap. However, I DO order dies that are .002" oversize. Not because I am going to shoot them that size, but because it allows me to continue getting a good fit with that mould as the barrel wears and the ball seat increases in diameter - I just use a bigger sizing die. And, quite often, you can have more than one rifle with similar leade/ball seat dimensions, so you can use one mould and two different sizing dies. From everything I have tried and read, sizing as much as .003" does not affect bullet performance.
If you are going to size and you're also heat treating, do the sizing pretty much immediately after casting - sizing affects hardness of the "skin" of the bullet, so do it early before the hardening process begins. Not a huge issue, but if you have to size anyways, you might as well do it when it will have the least amount of effect.
So, if you want more than just a few cast bullets for shooters (and if that's your aim, the commercially cast bullets are a hard thing to beat) using Ed's Load or whatever, slug your leade/ball seat or get some Cerrosafe and make a cast. If you don't want to bother with a custom sizer (and many, many don't and do just fine), simply choose the sizer that is one size smaller than the measurement of your ball seat. Don't worry about what the bore and groove diameters of your rifle really are.
Incidentally, speaking of what bore and groove diameters actually measure, I have a Long Branch with barrel measurements that belong on a .30 caliber - and I have a Husqvarna 30/06 with measurements that belong on a .303. So in any case, particularly with older rifles, I wouldn't be presuming that the bore/groove measurements are actually what they're supposed to be.
Making your own alloys. My short answer to that is I used to do it and just don't bother anymore - wheelweight works just fine once cleaned up, and it's great to be able to temper the bullets to the required hardness through heat treating. However, if you do have an inexhaustable supply of pure lead you want to use, and since you already have the tin, a bag of chilled shot (i.e. contains arsenic and antimony) is all you need to start producing your own equivilent to Lyman #2/WW. There are lots of sources available that will give you the various amounts you have to mix of each. One of the better ones is a spreadsheet available through the Cast Bullet Association. You plug in numbers and it tells you what you need to add of everything else to get what you're looking for. Here's the link for you:
http://www.castbulletassoc.org/downloads/alloycalculator.zip
Anyways, because I find making alloys annoying, I just use wheelweights. Believe it or not, I do like to keep things as simple as possible - while still getting good results, however. Many of the bughole shooters in the Cast Bullet Association matches also use WW, particularly with linotype getting increasingly expensive. If it is good enough for them, WW is probably good enough for just about all of the rest of us.
Heat treating in an oven is far more certain - and infinitely more controllable - than water dropping. This does require investment in some Temperil pencils or paint, and you do need to have a general idea of the working pressure of your load. You can get the pressures from powder manufacturers, which should put you in the ballpark, or buy/find a friend with Quickload. The bottom line is that you do want bullet hardness to match the requirements of the working pressure of your load. Of course, you can always do it backwards - harden the bullets and then adjust the load up and down until you hit the right operating pressures for the hardness. That's what most water droppers end up doing - they harden their bullets and then start adjusting powders and charges until they find one that works.
BTW, if you are going to water drop your bullets from the mould, take great - nay, extreme - pains to ensure there is absolutely no possible way for a drop of water to get into your molten alloy. Being painted with molten lead erupting out of a pot is one of life's experiences you probably will not enjoy.
Hardness is not a big issue if you just want "shooters" for your rifle - and I probably cast and shoot more "shooters" than anything else. At relatively sedentry velocities, just cast, lube, and shoot; no need to put more into your bullets than that. I don't even bother with gas checks. You don't need hardened WW bullets for relatively low pressure loads - in fact, you may make them too hard to obdurate properly, depending on the load you're using. But if you want best results for hunting and other high performance cast loads, you do need to adress the hardness issue. At least I believe you do.
Finally, seating. It follows that if your bullet is sized to fit the leade/ball seat of your rifle, it is more than possible that the expander ball on your conventional dies (sized for consistently sized jacketed bullets) may not do the trick. Lyman makes M dies (neck expander dies), as do RCBS and at least a few others. They are specifically intended for prepping a case for seating a cast bullet. For those not shooting cast bullet benchrest, I believe that an expander die that opens the case mouth up just enough that the bullet can be seated without being damaged is close enough. They will custom make a size for you for a small fee, or you can simply buy oversize plugs for the die and take them down to the size you want.
Cast bullets in rifles can be as simplistic as buying the ready to go jobs, seating them, and shooting them with a mild load. Or casting them from wheelweight, tumble lubing them, and shooting them as cast with a mild load. And it can get to the point where you get a gunsmith to adjust your leade/ball seat, invest in bump dies, etc. What I do find to be consistent is that the more initial preparation you put into your casting workflow, the better your results are. Getting the size of your ball seat only needs to be done once, ditto for your expander dies and sizers. After that the process is really no different.
I'll attach some data below. I have yet to figure out how to properly load tables or table format into these message boards, so you'll have to sort some of it out. Use it or ignore it as you prefer, but either way, have fun:
Cast bullet alloy metallurgy trivia:
Common BHN measurements:
Pure lead 5 BHN
Wheel weights 8-13 BHN, composition varies
Lead/linotype 15 BHN, half and half
Linotype 22 BHN
40-1 Lead-tin 8.5 BHN
30-1 Lead-tin 9 BHN
20-1 Lead-tin 10 BHN
16-1 Lead-tin 11 BHN
10-1 Lead-tin 11.5 BHN
Lyman No. 2 15 BHN
Heat treated 25-35 BHN, varies with heat treat and age
Wheelweights
After 6 weeks, air cooled bullets will reach maximum hardness.
This hardness can be further increased by heat treating.
HEAT TREATING WHEELWEIGHTS
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
Conclusions:
Exceeding 450 did not cause any significant increase in hardness.
460 deg was very close (read that too close) to the plastic deformation stage of the alloy
OPTIMAL HARDNESS FOR OPERATING PRESSURE OF LOAD
Tensile strength of lead/lead alloys = BHN x 480
Best bullet performance is usually at pressures between 3 and 4 times
Tensile strength.
ALLOY BHN TENSILE STRENGH (PSI) TIMES 3 GIVES
MIN. CHAMBER PRESSURE (PSI) TIMES 4 GIVES
MAX. CHAMBER PRESSURE (PSI)
PURE LEAD 5 5(480)=2400 7,200 9,600
1-20 Pb/Sn 10 10(480)=4800 14,400 19,200
WHEEL WEIGHTS 12 12(480)=5760 17,280 22,040
LYMAN #2 15 15(480)=7200 21,600 28,800
LINOTYPE 22 22(480)=10560 31,680 42,240
HEAT TREATED WHEEL WEIGHTS 30 30(480)=14400 43,200 57,600
VELOCITY REQUIRED TO EXPAND OR DEFORM VARIOUS HARDNESSES
BHN MINIMUM TERMINAL VELOCITY HOLLOW POINTS*
5 (Pure lead) 1200 fps. 700 fps.
8 1300 fps. 800 fps.
10 1400 fps. 900 fps.
14-15 1500 fps. NR
18 1900 fps. NR
20 2200 fps. NR
30-35 2400 fps. NR
NR - Not recommended for game shooting because of extreme destructiveness. Good for varminting, though.
* - Hollow point size and bullet nose shape affect required terminal velocity greatly, so these can only be considered approximations. Hollow points are best used with pure lead or tin-lead alloys as even small amounts of antimony cause bullet break-up. If antimony alloys are used, do not exceed 1 ½ % antimony or 10 BHN.
