Testing Alloys At 3150 fps

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Last Post 15 December 2016

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mtngun posted this 30 November 2016

The alloy shootout has begun!

This will use the same 7BR rifle and the same 100 gr. GC bullet that I used in my lube shootout, but just for the learning experience I will be using a different powder, LT30, and driving it a little faster.

I did some last minute load tweaking. I figured the hotter load might benefit from a more positive bullet fit, so I experimented to see how far out I could seat the bullet before it would get pushed back into the case. It turned out that it could tolerate 0.020” jam before the bullet began to slide back into the case, so I used 0.020” jam for the ladder test.

I am not a big fan of ladder tests because they do not commonly take into account random variation. Nonetheless I tried a ladder test, walking the powder charge up in 0.2 grain increments. All but two charges went into one ragged hole. Were the two outliers due to their powder charge, or were they due to random variation? We can't be sure without repeating the ladder test 10 or so times, so the ladder test was not very helpful. Nonetheless I settled on the top charge of 32.4 gr. because it went into the main group and I am a s**ker for more velocity. :D

A faulty extension cord caused my chronograph to conk out in mid-test so the velocity data is incomplete. But with this load I'm not overly concerned about chrono data because LT30 has been burning very consistently (though a bit dirty), with 30 - 40 ES being typical for 10 shots.

This will be the control load that other alloys will be compared to. I would have preferred a more accurate load, and in hindsight I might should have slowed it down to 3100 fps, nonetheless 1.5 MOA is accurate enough for comparison purposes. The fact that the RPM/velocity seems to be borderline for accuracy may actually be useful for alloy testing purposes, because the alloy plays a role in both the as-cast balance of the bullet and the as-fired balance of the bullet.

In case you were wondering, the group measurements posted on the target were measured in the field with a ruler while the group measurements in this table were Taran results. Sometimes the Taran measurement is a few hundredths different than the ruler measurement -- that's just normal measuring tolerances.

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yodogsandman posted this 01 December 2016

An interesting test!

How close is 470*F to your slump temperature?

What's your alloy?

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mtngun posted this 01 December 2016

Alloy was J.R. brand reclaimed shot. Let's see if I have the slump temperature wrote down somewhere ... here is what I found:

I heat treated a batch of reclaimed shot bullets the other day at 480F and 5 bullets in one particular spot in the tray slumped to various degrees. The remaining 60 or so bullets were fine, so apparently that one spot gets a little warmer than the rest of the oven.

Next time I'll try 475F. If I still get slumping then I'll try 470F, and so forth until the process is reliable.

I haven't had any more slumping problems with reclaimed shot since I switched to 470F. Your oven may be different.

This particular lot of J.R. shot was not particularly hard. Since reclaimed shot is not a controlled alloy, you never know for sure what you're getting. All of it is good stuff, but some lots are better than others.

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Standard Member

yodogsandman posted this 01 December 2016

I'm sure J.R. brand reclaimed shot is fairly consistent on a national level, compared to say, COWW depending on locality. I think the shot probably has about 4% Sb and no Sn? Do you add any Sn?

If I try for 470F with my COWW + 1% Pewter, I get discoloration and rough spots. So I stay at about 450F now, quench in ice water and get 30 +/- BHN after 5 days. I don't have to stay and babysit my convection toaster oven at that temperature either.

Your testing will probably open up my eyes and maybe get me to try some other alloys. Instead of adjusting powder for the hardness, adjust the BHN and alloy for max performance at HV.

Thanks for taking the time and components to do it!

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mtngun posted this 01 December 2016

No, I never deliberately add tin to either shot or WW.

Very few shot makers guarantee the composition, especially for their #7 1/2 & #8 which is what reclaimed shot is, so there's just no telling what's in there, but 3 - 5% antimony would be my guess. Shot is rumored to be (relatively) high in arsenic and I suspect that helps the harden-ability, too.

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mtngun posted this 11 December 2016

The new forum was not letting me post when I tested air-cooled Lyman #2, but you can catch up on it here if you like.

Today it stopped snowing long enough for me to do a little shooting, after shoveling a path to the target. :lol:   There was a 10-15 mph breeze that changed direction every few minutes, and some occasional light mirage, but overall conditions were decent, much better than the fierce mirage I struggled with last time.    I learned my lesson from last time and kept the mirage shade on the barrel at all times, and remembered to turn on the ventilation fan while shooting. :lol:

Today I tested oven-treated Lyman #2.    The sized bullets had been oven-treated at 470F for one hour and then quenched in water.   I had never attempted to heat treat Lyman #2 before since I normally don't care to shoot Lyman #2, but had heard of people on the internets heat treating it successfully so I just assumed it would work.   More on that later.

The oven-treated Lyman #2 performed much better than the previous test with air-cooled Lyman #2, though it was still prone to horizontal fliers. Most of the fliers “felt” like good shots so I'm pretty sure they were due to some failing of the bullet, not the fault of the shooter, nor the range conditions.

While air-cooled Lyman #2 left distinctive streaks of lead in the corners of the groove near the muzzle, oven-treated Lyman #2 left the muzzle clean as a whistle.

Stats:

At the end of the day I performed the usual hardness tests. You're thinking that oven-treating Lyman #2 must work a treat since it was more accurate and cleaner than air-cooled Lyman #2? There's just one problem -- the heat treating did not work! At 14 - 18 BHN, the oven treated Lyman #2 was not one iota harder than air-cooled Lyman #2! :lol:

Shootout summary to date:

Since the oven-treating did not work, today's test was merely a re-test of Lyman #2.     That's not necessarily a bad thing because my original test of air-cooled Lyman #2 was performed with sometimes fierce mirage.   At the time I didn't think the mirage had hurt groups that much, but maybe it did hurt groups because Lyman #2 did much better today.    Oh well, live and learn.

Today's accuracy improvement might be explained by the better range conditions, but how can you explain the improvement in barrel fouling?    I don't have an answer to that question.       It's one of those mysteries that drives cast bullet experimenters to drink. :lol:

As for why my batch of Lyman #2 (certified from Rotometals) did not heat treat, I can only say that it's my understanding that heat treatment of antimonial alloys is influenced by trace elements like arsenic.    Those trace elements are not necessarily tightly controlled so it's possible that some batches of Lyman #2 contain enough trace elements to heat treat, but my batch did not.    All I know for sure is that my particular batch of Lyman #2 is not heat-treatable.

I have at least one more alloy I'd like to try before I wrap up this shootout.

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Banned

David Reiss posted this 11 December 2016

Just moving the thread back to the latest.

David Reiss - NRA Life Member & PSC Range Member Retired Police Firearms Instructor/Armorer
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mtngun posted this 15 December 2016

Today we tested “enhanced” reclaimed shot.

First, I added one tablespoon of sulfur to 10 pounds of barely melted J.R. brand reclaimed shot.

Second, I added 0.8 pounds of Rotometals 30% antimony. Guessing that the reclaimed shot started out at 4% Sb, then the enhanced version would end up at 5.9% antimony. The bullets were oven treated at 470F and quenched in water. After aging approximately 2 weeks, the hardness today was 40.5 BHN (4mm, 60#) or 45.2 BHN (10mm, 150 kg), for a 6 - 8 increase in BHN compared to straight J.R. shot.

It was overcast, 20 degrees F, and dead calm, but nonetheless there was a bit of mirage. Looking through the scope, the target appeared to be jiggling up to 1/4” to and fro. I'm not sure if the mirage is happening at the target or in the muffler, but I'm suspicious of the muffler. More on the mirage problem later.

As usual, I fired 2 fouling shots through the cold, clean barrel before moving on to group shooting.

When I chambered what was supposed to be the first cartridge for score, the sear released as the bolt closed, so the gun wouldn't fire, and I had to eject the cartridge and try again. When I ejected the cartridge, the bullet remained jammed in the throat as is typical with my target loads, while the gas check remained in the cartridge neck. My normal procedure when a check gets stuck in the neck is to drill an 1/8” hole in the check, screw in a drywall screw, and yank on the drywall screw to remove the check. But if I had paused to do that, the barrel would have cooled off and I would have needed to shoot another fouling shot or two. So instead I seated the checkless bullet back in its case, knowing full well that it would probably push the check further into the neck, and fired it at a sighter target. That was a foolish thing to do, more on that later. For now I will note that group #1 was very poor, and in hindsight I'm wondering if that mis-checked bullet fouled the barrel and the fouling caused the wild shots in group #1?

Averaging 1.52", the enhanced J.R. shot tied with regular J.R. shot.

But at least the extra hard bullets managed a lucky MOA group.

Stats:

Summary To Date:

If, for the sake of argument, we dismiss group #1 due to possible fouling from the mis-checked cartridge, then the average for the remaining 9 groups would be 1.41", and the average mean radius would be 0.45". That's still not significantly better than regular J.R. shot.

Errant Gas Checks, oh my! At the end of today's session, there were two holes in the pexiglass end of my shooting muffler. You can't tell from the photo but both holes were below the top of the chronograph. I'm sure they were caused by gas checks, not bullets, because 1) it would have been physically impossible to shoot a bullet that low without hitting the chronograph and 2) there were no bullets unaccounted for on the target.

One of the errant checks may have been my fault, due to the mis-checked bullet that I discussed earlier. It was a dumb thing to fire it over the chronograph, but at least there is an assignable cause for the errant check.

But what about the second hole in the pexiglass? I have to assume it was due to a normal round losing its check. This 7BR barrel has never done that before, to my knowledge. Did it have something to do with the extra hard alloy? I can't rule it out, but on the other hand I just don't know for sure.

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mtngun posted this 15 December 2016

Mirage:   I can think of 3 possible causes of mirage at my range -- 1) outdoor mirage, 2) mirage inside the muffler, and 3) mirage caused by the warm barrel.    It's the latter two that I'm worried about at the moment.

If there is no ventilation, warm combustion gases accumulate inside the muffler and can cause mirage.   The combustion gases are also unpleasant to breathe.     Hence earlier this year I added a 4” computer fan to force air through the muffler, pushing the combustion gases out the far end.   It mostly works as intended.

When I remodeled the muffler recently, I piped the ventilation air so that it blows directly down onto the middle of the rifle's barrel.   The idea was that it would simultaneously cool the barrel and ventilate the muffler.     I suspect it will work as intended on a hot summer day, but ..... on a cold winter day, that cold ventilation air mixes with warm indoor air, or hits the warm barrel, and causes mirage because of the temperature differential.

Today I experimented with turning the fan off while firing. With the fan off, the target jiggled about 1/8", compared to 1/4” jiggle with the fan on.   Target #6 was shot with the fan off while firing, then letting the fan run one minute between shots to blow combustion gases out the muffler.    That method did seem to reduce mirage, but it was a nuisance to turn the fan on and off and the group was nothing to brag about, so I switched back to leaving the fan on all the time.

Then I experimented with a makeshift deflector that deflected the cold ventilation forward, instead of blowing directly on the barrel.   The deflector is simply an old target folded and stapled in place.     It seemed to help slightly, reducing jiggle to about 3/16".    Groups #9 and #10 were shot using the deflector.     I'm going to continue using the deflector until I come up with a better idea.

Getting back to the alloy shootout ..... I feel bad that the test of air-cooled Lyman #2 was confounded by serious mirage, so I'm thinking about retesting it. I want to give air-cooled Lyman #2 a fair chance to show what it can do.

I'm debating whether to add air-cooled wheelweight to the shootout. The upside is that it would provide a data point for a relatively soft alloy. I don't expect it to shoot well at 3150 fps, but nonetheless it would provide a useful contrast to the hard alloys in the test. The downside is that lead wheelweight is being phased out in my part of the country so I consider it an obsolete alloy, even though I'm quite fond of it.

Besides the retest of Lyman #2, and the possible addition of air-cooled wheelweight, there are no other alloys I plan to include. While I certainly have left out many alloys, I figure I will have covered a range from 11 BHN on the soft end to 40+ BHN on the hard end, and that should be adequate to prove whatever there is to prove.

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RicinYakima posted this 15 December 2016

Question. What is the function of putting Sulphur in your alloy mix? As a chemist I don't see what that would do. Does it make some type of bi-metal that alters the crystal structure? I find nothing in my texts. Thanks, Ric

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SierraHunter posted this 15 December 2016

I too am curious about the sulfur. 40 BHN is hard! Hardest I've ever seen was 24 BHN.

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mtngun posted this 15 December 2016

I refer you to Wiljen's superb article on the use of sulfur as a “catalyst” in hardening antimonial alloys.

That said, was sulfur helpful in this particular case, considering that shot is rumored to be high in arsenic and as such may already have ample “catalyst?" I don't know, since I did not do a with-and-without-sulfur comparison due to time and money constraints. My logic was that sulfur might help, but even if it didn't help, it wouldn't hurt.

Update: after carefully going over the sequence of events related to today's mis-checked cartridge, I edited my original post to offer a possible explanation for group #1's shotgun pattern. Even if we disregard group #1, enhanced shot is still statistically tied with regular shot, but it makes me feel better to have an assignable cause.