Bismuth/Tin PRB Testing

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Nuthatch

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I was given some bismuth/tin alloy to cast into patched round ball and test as an alternative to lead here in CA. Here's my write-up and some pictures in case anybody else is looking for lead alternatives so they can hunt with PRB where lead is banned.

Home Cast Bismuth/Tin PRB 09/2021



Prior to this experiment, I had no experience with home casting of bullets or round ball of any kind. It took some trial and error as well as the helpful advice from a member of muzzleloadingforum.com. I used an electric hot plate, set on its highest setting, with a 2” threaded pipe fitting for a crucible and a large washer underneath. Given the time it would have taken for the bismuth alloy to melt, I helped things along by heating the crucible with a blowtorch. As the mixture warmed, I added pieces of the ingot until I was able to get a reasonably full bowl and used the ladle provided to move some of the apparent slag off to the side. I also used the blowtorch to heat the aluminum mold a little. As I got closer to casting, I set this mold on the electric hot plate to keep warming and set the ladle inside the melted alloy to warm as well.



Care was used to only fill one of the six cavities at a time. After I filled the cavities, I waited about 2-3 minutes for the balls to harden and cool slightly. The mold was opened over a bucket of water where the balls could drop in and be immediately quenched. Most of the balls would not drop free of the mold, as I expected. I lightly tapped the balls with the same hammer I used to cut the sprue in order to get them to drop free.



In all, I cast 42 balls from the 1-lb ingot. There was some left over in the crucible but it was getting a little harder to get a full ladle so I stopped casting at that point.



I weighed each ball on my digital grain scale and measured them with calipers. Most came in right around 140 grains. All measured 0.4825 in diameter from the 0.480 mold, showing about 5% expansion. I decided to sort them so that I would do accuracy tests on the balls that were within 1.5 grains of 140 and use the rest for penetration tests at a later date.



About a week later, I went out to a range to do accuracy testing & get some chronograph readings. Rather than running the accuracy and chronograph testing together, I did them separately. If this had been a more scientific test, I would have recorded each shot’s impact and velocity. But I really just wanted to get a general sense of how the balls behave. All shots were done from 50 yards, although I did a few at about 20 yards when shooting into a berm to see if I could recover the projectiles. The rifle being used is a Traditions Woodsman with a 1:48 twist. The rifle has open sights that are enhanced with fiberoptic lines for visibility. Time was about 8:00 am until noon and I was facing into the rising sun with enough visibility to see the target clearly, although the bullseye was difficult to see when looking at the front sight before each shot.



My first group was 3 shots with a patched .490 ball over 90 gr Pyrodex RS (FFG). The ball and patch combination is extremely tight. The patches are 0.018 thick and my barrel is about 0.501. Although it seats fairly easily with a range rod, it would is very difficult to seat the ball with the fiberglass rod attached to the rifle. The 3-shot group measured about 1.5”. This is typical for me in this combination and why I chose it as a starting load for comparison. A fourth shot was made through the chronograph and measured 1806 fps.



My next group was with the home cast Bismuth/Tin alloy balls, which measured .4825. In my previous experience with ITX round ball, which is very hard, I have had to use a thinner patch than what I use for lead. This thinner patch, measuring 0.01” thick, seated very easily – almost too easily. I used the same 90 grain load. The group was significantly larger at about 3” CTC but about the same height on the target. Velocity measured 1928 fps.



About this time, I had gone to check the targets when I realized that a fair amount of my patch material downrange was in pieces and heavily charred.



To try and tighten up the group, I went back to the thicker 0.018” patch that I was using for the lead balls and added a lubed felt wad over the powder charge. I backed off to 70 grains Pyrodex and tested accuracy again. The group measured around 2” and the velocity was 1611 fps.



Satisfied with this result, I wanted to get a comparison with a commercial alternative – ITX. With a 90 grain charge, the 155 grain ITX ball measured 1739 fps. I did not get a chronograph reading at 70 grains. I did run the accuracy test at 70 grains, however. The 3-shot group had two shots touching and one flyer down several inches, which was likely my shooting error.



To further test accuracy, I did a 5-shot group with the Bismuth alloy. The total group size was over 4”. However, there were two shots touching high and left of the bullseye, two shots centered around the bullseye and one down about 2” from the bullseye. Although the group size is larger, it is likely that my form is starting to break down and I am not quite lining up the sights the same from shot to shot – something I have noticed that I do sometimes when shooting open sights.



To further test the velocity baseline, I did some chronograph readings of the lead balls at 70 grains of powder. Those shots came in at 1618 and 1606 fps.



I was able to recover some of the projectiles in the dirt mound behind the target. The I recovered 2 ITX balls, 4 Bismuth alloy balls and a few fragments of these that had shattered. No lead balls were recovered. I am not sure if the balls had fragmented upon impact, leaving nothing to find or if I simply didn’t find any. The only lead fragments I could find were around the steel gong I had setup and took several shots at. The recovered ITX balls retained 100% of their weight and showed little if any deformation. Both measured at 0.487 in diameter before and after shooting. I am confident that I could reshoot these balls again with little to no change in the point of impact from a new, unfired ball. The Bismuth alloy balls that I recovered measured between 130.6 grains and 136.6 grains. Diameters were ever so slightly larger at 0.491, 0.488, 0.4995 and 0.486. For all practical purposes, I’d say there was no expansion but 92.9-97.1% weight retention. However, there were some balls that had shattered and only fragments were found. So terminal ballistic performance may vary significantly. This may be due to my own faulty casting methods that give some balls more strength than others. It may also have been from the balls hitting each other or rocks in the dirt.



I feel that the Bismuth alloy is a viable alternative to lead for roundball shooters who want to home cast. The alloy is easy to cast, accurate enough within the effective range of an open-sighted patched ball shooter and hard enough to give good penetration on medium-sized game while holding together. Better casting methods could yield a more consistent ball and using a scoped rifle could offer more reliable data that, I feel, may give better results from which to make comparisons. Velocity is nearly identical with the loads I was using, as was the point of impact. Though the bismuth alloy balls are lighter than lead, they were also easier to stuff down the barrel due to their smaller diameter. Further load and patch development could yield a combination that is as-accurate as lead and may have higher velocities. While lead is likely to offer some expansion on impact, it isn’t entirely necessary with a 50-caliber. The bismuth alloy’s hardness may help lethality by giving better chances of a pass-through on game than lead. Further testing on water jugs or ballistics gel would help get a better sense of its potential advantages or disadvantages on terminal performance. At about $0.40 per shot, the alloy offers the home caster a more cost-effective option.



However, ITX appears to be a superior product that showed better accuracy and tighter tolerances from the box I was using (all were within 1.1 grains of each other). It is also held together extremely well. So I would expect that it would achieve remarkable penetration. Expansion would probably be non-existent on game animals. But there are two main drawbacks to ITX that I can see. The first is the hardness. While it can aid penetration, I would hesitate to use ITX for hunting in areas where the terrain is very rocky. The lack of deformation may increase the odds of a bad ricochet, even after exiting an animal. The second is cost. ITX costs $1 each before shipping – over twice that of the bismuth alloy.
 

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Historian

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Very good write up sir. Some questions though. I make my shot and RB so I am curious, do you know what the ally ratio was? For loose shot I use 95%/5% bismuth tin ratio. For round ball I use 90%/10% bismuth tin ratio. Also did you think about using a intermediate sized patch material for the bismuth round balls? Your group may shrink with a little bit tighter patch material for the bismuth RB's. Mine did. Yes, you are correct bismuth will expand ever so slightly when it cools. Also I use a "mold release agent" from Frankford Arsenal which greatly helps release the bismuth round balls. Try some and it will make a difference. Great article thanks for posting sir.
Rob.
 

Nuthatch

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Very good write up sir. Some questions though. I make my shot and RB so I am curious, do you know what the ally ratio was? For loose shot I use 95%/5% bismuth tin ratio. For round ball I use 90%/10% bismuth tin ratio. Also did you think about using a intermediate sized patch material for the bismuth round balls? Your group may shrink with a little bit tighter patch material for the bismuth RB's. Mine did. Yes, you are correct bismuth will expand ever so slightly when it cools. Also I use a "mold release agent" from Frankford Arsenal which greatly helps release the bismuth round balls. Try some and it will make a difference. Great article thanks for posting sir.
Rob.

The guy I was testing this for didn't buy it himself. But he thinks it came to him from Rotometals. Their alloy is listed as 87% Bi, 12% Sn, <1% Sb. I don't know who else makes Bi casting alloys so I'd say that's pretty reliable. The guy I got it from is from the Institute for Wildlife Studies here in CA. He's a hunter but doesn't hunt with traditional muzzleloaders. They were giving a presentation about lead fragmentation and lead free ammo at a range day for Backcountry Hunters and Anglers down in So. Cal and I expressed my frustration in finding lead free alternatives for round ball. That's when he offered to let me try it out & let him know how it goes. I think he got it from somebody else who wanted to test it but he doesn't have a gun that can shoot patched balls and didn't know of anybody who did before I came along. They've got water jugs & such for their demonstrations (typically done with a 30-06) so that's next once the weather cools out here. If it can pass a jug test and I can do it before November, I might just take it with me on my next hunting trip in Dec where I have decent odds of at least getting a doe to offer a shot, if not a buck.

Patch-wise, the thicker 0.015 patch with the felt wad was what grouped well with the 70 grain charge. The first shots with the Bi and 90 grain charge were done with a 0.01" patch and loaded pretty easily, though accuracy wasn't great. So after those first 3 high shots, I switched to the 0.015" patch, felt wad and 70-grain charge. I'd think a 0.02" patch (going up in size) would work well if I could find it. But, on the other hand, the lead 0.490 balls and 0.015" patch are very tough to load. My barrel is right about 0.501" so that's a bit oversized for sure. But from previous shooting, I found that a 0.01" patch with the 0.490 lead couldn't hold much of a group at all with more than about 50 grains of powder. It took the 0.015" patch to get it good and tight enough to hold a group well with a full hunting charge. It's so tight that I have trouble getting it down with my field rod. So I suspect that even if I could get more accuracy out of a 0.02" patch and the Bi roundball, it might be a moot point in the field if I can't load it with that flimsy fiberglass rod. I should add that where I hunt deer with a muzzleloader, I'm about 7 miles into the backcountry and staying for 3-5 days. So I'm not packing a range rod in that far. It has to work under those conditions for me or it isn't going to work at all. People who hunt closer to roads might be able to make it work just fine.

Releasing agent is a good call. Never done the casting thing before so I just don't know what I don't know. Thanks.
 

Historian

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As for intermediate patch sizes, try Track of the Wolf, October Country, Dixie Gun Works ect. You might try a different lube as well to help with loading? You want a good fit but not so tight you cannot load it in the field. I understand what you mean by that too. I generally shoot smooth bores which makes loading easier compared to a rifle. I have good accuracy out to 50 yards. Keep at it and it will be worth it. BTW what is the Jug Test about?😁
 

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Gentlemen, here are some pictures of raw shot that has just been made. It has not been tumbled yet to remove the sprue marks. Pictures are of 95% bismuth and 5% tin ratio of #1 buckshot, 0.20 T shot and .60 RB. The .60 RB due to expansion measures at .605.
 

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Historian

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The .605 RB will be used for deer and hog hunting on a NWR, Wheeler Wildlife Refuge where non toxic ammunition is required. The 0.20 T shot is for goose hunting where legal like here in AL. The 0.30 #1 buckshot will also be used deer hunting on the NWR. I really like the molds from Marty's Arms. They seem to work really well.
 
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