Copper/Tin/Antimony/lead alloy rifle boolit results

[oldandslow]

Hi casters, 7/22/13

I have been trying to get my 30-06 AccurateMold boolits (#310-180grain-F-gas check) boolits to achieve a medium velocity (2200 ft/sec) with both accuracy and hardness/toughness. The problem is that the long, unsupported nose forward of the driving bands twists/sheers off at velocities above 1800 ft/second. Thanks to the many posters who suggested fixes from my last post about "Recovered boolits..." and suggested that the alloy I was using was too brittle and I needed to add tin (Sn) or just keep the velocities down. Since then I've read a number of the posts on adding copper for toughness and have tried a couple of alloys in addition to the added tin.

First- the base alloy used above is 97.18% lead(Pb), 2.22% antimony (Sb) and 0.435% tin (Sn) from Rotometal's analysis. The boolits are shot into wetted paperbooks and generally recovered at the 16-19" layers. The boolits are then weighed and the recovered weight used as a measure of their "toughness." The boolits are "push thrugh" sized to 0.3105" for a mic'd bore slug of 0.3087" and gas checked (Hornady) at sizing. Powder is 40 grains of 4064 in a recently bought Howa 30-06 which shoots 1.5MOA with FMj's.

Base alloy above- recovered wt.= 68 grains (38% retained weignt). Nose is twisted off and only base with driving bands recovered. (Ice water dropped/BHN=16.6).

Base alloy above plus 2% added SN- 114 grains (63% retained wt.). Nose twisted off. (Ice water dropped, BHN=16.6).

New alloy #1- 94.9%PB, 2.3%SB, 2.79%SN, 0.1125%Cu after adding known amount Rotometals alloy (Sb-4.5%, 91%Sn, 4.5%Cu) to base alloy. Results =104grains (58% wt. retained) for Ice water dropped BHN 15.4 at 60 hours. Interesting the 70degree water dropped same alloy had 131 grain wt retention (73%).

New alloy #2- 93.5%Pb, 2.3%Sb, 3.9%Sn, 0.27%Cu. (50% more tin and more than double the Cu concentration). The Ice water dropped recovered boolits showed 128 grains(64% retained wt.) and the 70 degree water dropped boolits at 154 grains (85% retained weight).

So in summary adding Sn improved recovered boolit wt. significantly and adding Cu to the 2%Sn alloy seems promising but they still are losing a lot of weight (recovered wt. for same boolit with the 2%added Sn but minus the Cu at velocity of only 1845 ft/sec gives a 96% wt. retention.).

So what would you do next to increase toughness and keep the nose attached to the boolit base? Increase the Sn or Cu or Sb content (I've got another ingot of the Rotometals Copper alloy and two of Superhard ingots)? Another approach might be to just order another boolit mold from AccurateMolds without the unsupported nose profile.

best wishes- oldandslow

[Lefty SRH]

What exactly are you buying from Roto Metals? I've been using the equivalent to Roto #2. May want to try some air cooled boolits.

[oldandslow]

lefty,

The Rotometals alloy is their Number 1 Babbitt bearing alloy with the compositon of 91% tin, 4.5% antimony and 4.5% copper. It's one of the few copper containing alloys that will melt at the lower temps of lead casting.

My base metal alloy is from my local scrap dealer. I got a ton of same-source alloy and sent it in to Rotometals for analysis so I could have an accurate metal composition number with which to alloy (otherwise it's all guesswork).

Regarding the air cooled option- that was tried initially with the same boolit in 30-30 loads and 30-06 loads. I was getting keyholing on most shots at 25 yards and only half of the boolits would hit a two foot wide cardboard at that same distance. When I switched to 70 degree water dropped or ice-water dropped (after 60 minutes at 465 degrees) the keyholing disappeared and the accuracy became acceptable although only at 30-30 velocities (1800 ft/sec). So at least for me water dropping cured my boolit fragmentation problems at less than 1800 ft/second compared to air cooling.

Now the challenge is to get boolit integrity at mid range 30-06 velocities of 2200 ft/sec.

best wishes- oldandslow

[badgeredd]

Hi casters, 7/22/13

I have been trying to get my 30-06 AccurateMold boolits (#310-180grain-F-gas check) boolits to achieve a medium velocity (2200 ft/sec) with both accuracy and hardness/toughness. The problem is that the long, unsupported nose forward of the driving bands twists/sheers off at velocities above 1800 ft/second. Thanks to the many posters who suggested fixes from my last post about "Recovered boolits..." and suggested that the alloy I was using was too brittle and I needed to add tin (Sn) or just keep the velocities down. Since then I've read a number of the posts on adding copper for toughness and have tried a couple of alloys in addition to the added tin.

First- the base alloy used above is 97.18% lead(Pb), 2.22% antimony (Sb) and 0.435% tin (Sn) from Rotometal's analysis. The boolits are shot into wetted paperbooks and generally recovered at the 16-19" layers. The boolits are then weighed and the recovered weight used as a measure of their "toughness." The boolits are "push thrugh" sized to 0.3105" for a mic'd bore slug of 0.3087" and gas checked (Hornady) at sizing. Powder is 40 grains of 4064 in a recently bought Howa 30-06 which shoots 1.5MOA with FMj's.

Base alloy above- recovered wt.= 68 grains (38% retained weignt). Nose is twisted off and only base with driving bands recovered. (Ice water dropped/BHN=16.6).

Base alloy above plus 2% added SN- 114 grains (63% retained wt.). Nose twisted off. (Ice water dropped, BHN=16.6).

New alloy #1- 94.9%PB, 2.3%SB, 2.79%SN, 0.1125%Cu after adding known amount Rotometals alloy (Sb-4.5%, 91%Sn, 4.5%Cu) to base alloy. Results =104grains (58% wt. retained) for Ice water dropped BHN 15.4 at 60 hours. Interesting the 70degree water dropped same alloy had 131 grain wt retention (73%).

New alloy #2- 93.5%Pb, 2.3%Sb, 3.9%Sn, 0.27%Cu. (50% more tin and more than double the Cu concentration). The Ice water dropped recovered boolits showed 128 grains(64% retained wt.) and the 70 degree water dropped boolits at 154 grains (85% retained weight).

So in summary adding Sn improved recovered boolit wt. significantly and adding Cu to the 2%Sn alloy seems promising but they still are losing a lot of weight (recovered wt. for same boolit with the 2%added Sn but minus the Cu at velocity of only 1845 ft/sec gives a 96% wt. retention.).

So what would you do next to increase toughness and keep the nose attached to the boolit base? Increase the Sn or Cu or Sb content (I've got another ingot of the Rotometals Copper alloy and two of Superhard ingots)? Another approach might be to just order another boolit mold from AccurateMolds without the unsupported nose profile.

best wishes- oldandslow

oldandslow,

IMHO you are ALMOST there.

I have mentioned it several times and I think you've missed it. Your alloy needs to be "balanced". By that I mean, you need to keep the tin content equal or very nearly equal to the total of the Sb and Cu. In the highlighted area of the quote above you have more tin, about 1%, than you need. If your Sb+Cu = 2.57% the tin content should be very close to the same. If your Sn is at 3.9% then the total of the Sb+Cu should be very near 3.9%. So far in my experiments, I have found the best alloy seems to be around 3.25% balance +/- 0.25%. Higher than 3.75% seems to give a fellow an overly hard boolit. Less than 2.75% seems to be too soft for higher pressure loads. These numbers are assuming water dropped in room temperature water or about 70 degrees F.

Rotometals sells type 1, 2, 3, 11 babbit and all are useable for our purposes. I have worked with #2, #3, and #11. It is my belief based on my testing to date that one benefits more with a Cu content in the 0.25% +\-0.05% than higher content. The lower content level will improve the toughness, but seems to give up the strength of the alloy (for high pressure loads) below 0.15%.
I also have found that as the Cu content goes up, so must the casting metal temperature. At 0.2 -0.25% Cu content I run my metal temp at or slightly above 725 Degrees.

I am not claiming to have all of the answers but my experience to date seems to point in the direction I have outlined.

Edd

P.S. From my experiments, I favor 3# and #11 type babbit for the higher copper content of 0.2 to 0.3%.

[357maximum]

Edd is dead on and trust me when I say if you get the tin waaay to high compared to the CU+SB your boolits take a few months+ to "mature" in both size and hardness....size mostly though. They'll still shoot fine if you are the patient type....I am not. :mrgreen:

[Harry O]

oldandslow,

IMHO you are ALMOST there.

I have mentioned it several times and I think you've missed it. Your alloy needs to be "balanced". By that I mean, you need to keep the tin content equal or very nearly equal to the total of the Sb and Cu. very close to the same.

Edd



I have no experience with copper, however, I have experimented quite a bit with antimony. Antimony increases the hardness much faster than tin does. However, it is brittle and hard to cast with.

I have good results when the amount of tin equals the amount of antimony. They cast well and hold together.

When the tin is less than the antimony, the bullets are harder to cast and are more brittle. I have had high antimony-low tin bullets that have cracked through the diameter of the bullet when the case was crimped. Naturally, I did not even try to shoot them.

I also agree with .357max that high tin bullets take longer to harden. I am more patient, though.

[popper]

Your WD tests show the problem. Room temp isn't as brittle as ice dropped. Normal. Did you have any arsenic in the alloy? It is a grain refiner - deglobber for Sb. Cu links into the lead matrix. Consider a 2D array of dots. Force applies to a row of dots causes it to slide over the adjacent rows. Replace a dot of lead with Cu or S, the force required to slide the row is increased. Cu also combines with Sb to form a tougher alloy. Edd & I differ in that I don't use any Sn. It mixes with the Sb but does allow fingers of SN &. sb which are brittle and weak. I have no way presently to recover any ormshOot at anything but paper. Hope this helps.

[oldandslow]

Casters, 7/23/13

Thanks for all the replies. I'm especially grateful to the copper casting master's input; Edd, 357max and popper as I've tried reading most of your posts on copper alloy casting.

So it sounds like I need to increase the Sb percentage in my #2 alloy ((93.5% Pb, 2.3% Sb, 3.9% Sn, 0.27% Cu) so the Sb plus Cu percentages equal the Sn percentages while keeping the Cu percentage in the 0.225-0.25% range.. I should be able to do this with some of my Rotometals Superhard ingots (Pb and Sb) in the proper proportions.

Does this sound like a reasonable next step? And is there an alloy percentage where maximum toughness is obtained and I should go to another mold design to prevent nose fragmenting at medium velocities (2200 ft/sec)?

thanks- oldandslow

PS- Harry-thanks for the input. In my first try with my base alloy, 2.2% Sb and 0.435% Sn I added 2% pure tin to give a nearly equal percentage of Sb and Sn but was still getting only 40-56% wt retention at 2200 ft/sec. It may be that my long unsupported nose on my boolit will just not stay intact at velocities over 1800 ft/sec no matter what the alloy.

[popper]

long unsupported nose on my boolit will just not stay intact Note from my 2D analogy. A spinning CB hits the target, nose begins to mushroom and stops spinning, but the base still is. Slippage (fracture) resistance is related to the length of the row (or column) and in your case, the diameter of the nose. A while back I tested strength by twisting CBs to fracture. Looked like I used a chop saw on the front edge of the lube groove, about 30 of them, all the same. My conclusion is that a large meplat not only causes greater transfer of energy but withstands the impact forces better. Of course the alloy has to be up to the job. Look at some of 303guy's recovered CBs, mushroomed & twisted noses.
Edd, Larry and others here with much more experience like tin in their alloy. I just cannot find any theoretical reason for a large % of it. It does make mould fillout better. Arsenic forms a core inside a small Sb ball, preventing the Sb from creating a long weak finger structure. Tin likes tin so well that the atoms move to find each other even in the solid. That allows the weak finger structures to form. I found that cooking the Cu alloy for 30 min or so before casting made a stronger alloy. Sorry I didn't post this last nite but my B.P. was up from some postings on another thread.

[Echo]

I may be way off base here, in this alloy discussion, but have you tried a slower powder? Like 4831? A case full won't generate unsafe pressures, and might generate a slower acceleration, that might be a good thing.

[badgeredd]

oldandslow,

Echo made me think of something we have found with most cartridges we have using with the copper enhanced alloys. Powder selection will make a significant difference in accuracy regardless of the alloy. I have grown fond of Quickload to give me an idea of what powders will give me the best accuracy, theoretically. Generally it seems to work out. IF one uses a quicker powder, which in turn gives a lower muzzle pressure, one will obtain better accuracy, most of the time.

Yes you're on the right track by adding Superhard to up the antimony, but like I said earlier, my best alloys have been between 3.25% to 3.75% Sb. What seems to make the most difference in making a bullet with very good tensile strength and malleability is a balanced alloy. Too much Sn, or Sb will really affect the alloy strength. Too much Cu tends to make the alloy hard to cast with and also seems to cause inconsistencies in a batch of castings.

As far as maximum toughness, I believe one gets to a point of diminishing returns with more than 0.3% Cu or an Sb content of higher than 3.75%. Let me emphasize, that is my opinion.

Edd

[Changeling]

Hello oldandslow. I don't have a lot of casting experience but I do read a lot. I was wondering if you are quenching as you take the bullets out of the mold, I didn't see where you were unless I missed it.

Also. I read an article on hardning alloy, the man was using WW and explaining what elements were neeed to make a tough hard bullet.
"Arsenic" was a key ingrediant in trace quanties and was at the time found in clip on wheel weights. Does the alloy you are using have it?

[303Guy]

76973 Around 2000fps? Maybe less.
76974 2040fps

Weight retention near 100%. Alloy quite soft.

This is a tin/copper alloy which may or may not have some antimony in it. I've had a 'bad' alloy that would form softer bands and once I recovered a boolit that had obviously twisted on such a plane as it was launched out the case. The twisting showed up with rifling shear above and none below the twist plane. That plane was a shut fault as the lead stream poured down the centre of the mould.

[oldandslow]

greetings casters, 7/24/13

Popper- I have no Arsenic in either my base alloy (97.18% Pb, 2.22% Sb. 0.435% Sn analyzed by Rotometals) or either my Babbitt grade #1 (91% Sn, 4.5% Sb, 4.5% Cu) or Superhard alloy (30%Sb, 70% Pb) bought from Rotometals. At present I don't have an easy way to obtain any Arsenic although I will keep my eyes open. And I hope your BP is better- I'll try not to aggravate it here.

Echo- I'm in a really remote part of the US where UPS and Fedex don't deliver so I'm limited to what little powder my local supplier has- either 4064 or 3031 in rifle powders.

edd- I've run some numbers on my alloys and should be able to mix up a batch of my alloy #3 with 92.5% Pb, 3.7% Sn, 3.54% Sb and 0.25% Cu. This should give me a balanced mixture where the % of Sb+Cu equals the % Sn. I'll mix it up tomorrow and should have boolit recovery results in a week or so if things go well.

changeling- I have no arsenic in my alloys. Your thoughts are similar to Popper who likes arsenic. I'm still looking for an easy source. As to the water quenching- first I drop the boolits onto a soft cloth and inspect them. Then, somewhere in the 1-3 days later range I heat them up to 450-465 degrees in my oven for an hour on an old cookie sheet (temp checked with thermometer and the cookie sheet is never used for food). Then I water drop them into either ice water or 70 degree tap water. I measure their BHN hardness about 1 hour later, and then at 24 and 48 hours and then a day or two later. After 48 hours I see little additional hardening.

303guy- nice looking recovered boolits. Any idea of what copper percentages are in your alloy?

best wishes- oldandslow

[303Guy]

Copper would be pretty low. I'd be guessing at around 0.25%. I got the idea that the eutectic level was best from a segregation point. The allow that had soft planes was a little high on copper.

[popper]

7 or 8 chilled or magnum shot has arsenic. I only go to 400F to prevent slump & don't have any tin which lowers slump temp. Check them for slump from HT. An off center nose will cause the bent CB to break around the CG. I tried 1% Sb, 1% Cu with & without As, they shot the same in 30-30 & 308. That's a 20" 1:10 so the fps isn't like a 06. I don't find much additional hardening after 24 hrs. Just saw you are using the 31-180F which is like my 31-165A with a longer neck, mine has a semi-bore riding section before the ogive and shoots very well. Both have a small meplat. Closest I've gotten to recovering a CB was punching a RD311165(~ 2x the meplat) through 3" of white pine 2x4 @ 50 yds, a nice hole till the last 1/2" split out. No sign of any lead in the hole. Another issue you may consider, terminal energy. At 50yds, 180gr @ 2200 is 1780fp, @ 100yds is 1650 fp. At 10 yds, 1900fp. At 50, my 30-30 load is ~1400fp. What distance are you shooting the wet books? Alloy must be able to take the launch and the hit. Remember, though the CB takes the launch at high energy for 500 Usec, the hit dumps that energy in half that time for a 'soft' target, instantaneously for a 'hard' target. you indicated your HT eliminated the keyholing. I suspect the harder alloy size larger as well as harder. I'd recheck your size - make sure what you are seeing is not caused by almost keyholing.

[303Guy]

I've now had a boolit 'separating' in the middle! These are 224 RCBS FN's and velocity would have been moderate for a hornet - 10grs Lil'Gun. It looks simply like the front portion broke of but not so, the nose expanded right back over the boolit and separated when it encountered one of the grooves - crimp groove by the look of it. My summer camera doesn't work in winter so I can't take picks (I could warm the camera .... ). Yes we do have winter of sorts in NZ (I'm in the north where it doesn't snow and in fact, we don't even get frost where I am).