I have been prompted to try more tin in my hunting alloy. This comes from Larry Gibson’s advocacy, and also from a chapter by Dennis Marshall in “Cast Bullets” (NRA). Whilst the primary motivator is better ductility and hopefully better bullet performance on game, there are other aspects to increasing the tin.
The narrative from Dennis Marshall is that tin alone, while improving casting, has only a limited effect on hardness. The combination of tin with antimony in the intermetallic compound SnSb however gives the tin a similar hardening effect to antimony. This is borne out by the plot of hardness versus tin and antimony %, pages 17 & 131 of “Cast Bullets”. Straight 10% antimony indicates a BHN between 16 and 18, as also does 8% antimony with 2% tin, and 6% antimony with 4% tin, with 5% and 5% (Lyman #2) indicating 16. Once the tin % exceeds the antimony % this effect no longer applies to the extra tin.
I have posted before about using bullet weight as a measure of “non-lead” and thence an indirect measure of hardness. Lead is denser than tin or antimony. Tin and antimony are of nearly equal density and have a similar effect on hardness provided tin % is less than antimony %. Therefore “non-lead” can be determined from comparative bullet weight and should be a pretty good proxy for hardness – all provided that tin % is less than antimony %.
In using the bullet weight technique, I find the hardness I want by trial and error. My “lead” sources – lino, wheel weights, range scrap and mystery metals – are melted on their way to becoming ingots, and a trial cast of 20 or 30 bullets is made from each so that ingots can be labelled with bullet weight. When I need a new brew I can mix as required from the labelled ingots. I don’t actually need to know the precise non-lead %, just the bullet weight I require, since bullet weight will equate to hardness.
The application is my .30-30 hollow point bullet #U321297HP, intended weight 170 gns as cast, sized to .312”, with the 10 gn hollow about half the depth of the bullet. Muzzle velocity is approx. 2200 fps.
The alloy I have used thus far is diluted linotype, current batch 169.5 gns as cast and 16 BHN on my friend’s Lee tester. This alloy shoots well and the hollow point bullets kill well. The noses break up and create a cone of destruction. The bases hold together, defying the widespread prediction that they will “shatter”, and these bases penetrate a long way. The few bullets recovered appear as wadcutters, ground down to be a little shorter than the non-hollow part of the original bullet. This alloy of course already has some tin in it, perhaps 2% or 2.5%, courtesy of the linotype. Adding more tin is about more nearly balancing the tin and antimony content of the alloy.
For the current test I sacrificed a pewter beer mug, plus lino and wheelweights. According to the spreadsheet calculator I should have 5.5% tin, 6.8% antimony and a BHN of 16.5. My friend’s Lee tester says 16 BHN, the same as my regular alloy. Bullet weight is 169 gns as cast.
The alloy with more tin has performed well. Penetration when required (mature boar and big sow) was adequate, and destruction on soft rib shots of smaller pigs was likewise effective. There is no evidence of exiting bullets being other than just the bases or pieces thereof, so the promise of bullets holding together better appears unfulfilled.
Results have been similar to what I have come to expect from the diluted linotype alloy, though there is a suspicion that the new alloy, despite being the same 16 BHN, is expanding or breaking up slightly more. I have another 25 cartridges, plus another 300 bullets, softer this time at 15.8 BHN (5% Sn, 6% Sb as per calculator), so will know more when I’ve shot them off.
I would stress that these conclusions apply to hollow point 175 gn .30-30 rifle bullets at 2200 fps, as described, used on pigs. Bigger animals, larger or smaller calibres, and different velocity could require softer or harder bullets or a different hollow.
Herewith some results on pigs with the new alloy in .30-30:
- Young mature boar (58” snout to butt of tail) at 100 meters, frontal shot with angle, aimed centre of mass, entry at side of neck, bullet sized exit hole at diaphragm. Boar ran 70 meters. Typical for a frontal chest shot.
- Young sow, came into waterhole as per game camera, standing shot at about 20 meters. Broke both shoulders with .30 cal exit hole. Pig went straight down.
- Big sow trotting at about 50 meters. Double shoulder shot. Went straight down. Small exit hole from a bullet fragment. Gas check and more fragments found close to the skin.
- Small sow frontal shot at about 5 meters, to point of shoulder. Went nowhere. Elongated entry hole. Shoulder was well smashed, and inside chest a mess. No exit.
- Immature boar and his mate came to carcase. Camera revealed timing. Pre-dawn approach to about 50 meters. Pig on the right is the victim. Shot in the dark with NV attachment on rifle. Entry and exit wounds high just behind the shoulder. Pig dropped in his tracks. Sorry about the poor image - some early morning fog involved.
- Another immature boar, probably the other one in the image. Arrived at carcase early evening on his own a couple of nights later. Almost identical shot to previous one with same result.
