Alloy Shootout At 3150 FPS

[mtngun]

The lube shootout at 3000 fps was fun so next up is an alloy shootout at 3000 fps.

I haven't decided if the same 7BR load will be used.

Tentative list of alloys to test:
-- a yet undetermined "superhard" alloy
-- heat treated reclaimed shot
-- heat treated wheelweight
-- linotype
-- heat treated Lyman #2
-- air cooled Lyman #2

That leaves out a lot of alloys but it's 600 shots so hopefully it'll be enough to shed some light on the subject.

It'll take me a while to get all the bullets cast and prepped and find time to shoot 'em in decent weather, so this project may drag out for several months.

[Irishtexan]

Plus you have winter coming on, doesn't leave much time to fill the freezer.

[mtngun]

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 sucker for more velocity.


I may have bit off more velocity than I can chew because groups averaged a mediocre 1.52" and none hit one MOA. 164,000 rpm is a tough environment for lead bullets.


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.


As per my standard procedure the barrel was not cleaned between groups. Two warm-up shots were fired at the beginning of the day, and 1 warm-up shot was fired after pausing to reload shells. At the end of the day a single patch wetted with Ed's Red was pushed through the barrel to prevent corrosion. There was no fouling on the patch other than black carbon. I did not bother to borescope the barrel looking for leading because there were no symptoms of leading -- the last group was just as accurate as the first group, and there was no lead on the patch.

Here is how I arrive at the BHN's that I will be posting in this shootout. At the same time that I cast the bullets I also cast a couple of 45 caliber cylindrical slugs that are handy for BHN testing. The 45 caliber slugs are heat treated along with the bullets. Then I do the BHN tests on the same day that I do the shooting so that any age hardening is accounted for. 4mm and 10mm tests give similar results up to 21 BHN but above that they diverge, with the 10mm test giving a higher number. Since I never figured which test was right and which was wrong, I will simply measure the harder alloys with both tests and report both numbers.

[mtngun]

Today I tested linotype. I used certified linotype from Rotometals so there would be no doubt about the composition.

No matter how hard I try to design an experiment that is an apples-to-apples comparison, life always throws me a few oranges. At about 92.5 grains ready-to-shoot, the linotype bullets were lighter than the reclaimed shot bullets and hence they flew faster with the same load. If I had attempted to reduce the powder charge to compensate for the higher velocity, then the pressure with linotype would have been lower than the pressure with reclaimed shot load. Oh well, I'm just going to use the same load for all alloys and let the velocities be what they want to be.

Once again, there were no MOA groups. It just couldn't avoid the occasional flier -- not surprising considering the velocity and rpms (165,000).


Stats.


Summary to date:


Surely the 0.15" larger groups are not statistically significant? To my surprise, a T-Test says there is a significant accuracy difference between J.R. reclaimed shot and linotype.
-- 83% sure linotype is less accurate, going by the mean radii.
-- 68% sure linotpye is less accurate, going by group sizes.

[mtngun]

The alloy shootout at 3150 fps continues in the M700 7BR, today with air-cooled Lyman #2. The outdoor temperature started out at 16 degrees F and warmed to 20 degrees, but it was sunny and dead calm. Sunny and dead calm is not necessarily a good thing because you want a gentle breeze to dissipate the mirage. With no breeze, the mirage ranged from annoying to fierce.
.
Lyman #2 did poorly, averaging 2.14" for 10 shots at 100 yards. That's not surprising at this velocity and pressure, nonetheless I included Lyman #2 in this shootout because it is a popular alloy. 


The breech end of the barrel was squeaky clean after firing air-cooled Lyman #2.


But the muzzle end of the barrel showed a little streaking in the corners of the grooves.


Stats:


Alloy Shootout Summary to date:


Was Lyman #2's poor performance statistically significant? A T-Test using the mean radius data was 99.8% sure that Lyman #2 was less accurate than reclaimed shot.

I'm no stranger to shooting in mirage, but at times today it got so bad that I couldn't make out the aiming points (pen lines) on the target. Apparently when I paused to reload shells after target #5 I had turned the ventilation fan off and forgot to turn it back on when shooting resumed for targets #6 and #7. By #7 I was having a hard time focusing on the target. By #8 I was beginning to wonder if there was something wrong with the scope. The 36X Weaver looked foggy. A 36X Sightron seemed clear when I held in in my hands, so I aborted #8 to swap on the Sightron. Yet once the Sightron was mounted on the rifle, it was foggy, and the Weaver was clear when I held it in my hands. What the heck? Maybe heat rising from the barrel was blurring the scope's vision? So I slapped on a mirage shade and clarity improved 50%. Aha ! I had bought the mirage shade a while back but only occasionally used it because it hadn't seemed to make a difference unless the barrel was hot, and the barrel was only ~100F max today. But apparently the cold outdoor air was rising when it hit the 100F barrel. OK, lesson #1, always install the mirage shade.


Then I noticed that the ventilation fan was turned off. Oops! The fan helps exhaust combustion gases from the muffler, both for health reasons and to reduce mirage inside the muffler. With the fan on and the mirage shade installed, the target once again looked sharp in the scope. Lesson #2, always have the ventilation fan on while shooting.

Perhaps target #7 should have been tossed out due to mirage, but its horizontal fliers felt like good shots, and even if #7 had been disregarded, the other groups still had a poor average.

While conventional wisdom holds that Lyman #2 is 14 - 16 BHN, this certified Lyman #2 that I purchased from Rotometals measured 17.7 BHN using a 10mm / 150 kg test, and 18.6 BHN using a 4mm / 60lb test. I dunno what's up with that, perhaps the bullets air-cooled fast enough to induce a little precipitation hardening?

[mtngun]

It stopped snowing long enough for me to do a little shooting, after shoveling a path to the target. 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.


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!

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.

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.

[mtngun]

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 cartridge fouled the barrel and that 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. If I could do that every time, I'd be a happy caster.


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.

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.

[mtngun]

After thinking it over very carefully, I decided to perform a do-over on group #1 of enhanced reclaimed shot. Immediately before shooting the original group #1 I had fired a "mis-checked" round, with the gas check not properly attached to the bullet. In hindsight I believe the mis-checked bullet acted like a plain base bullet -- imagine firing a plain base bullet at 3150 fps! It must have leaded the barrel, causing the next several shots to be inaccurate.

So I retested the enhanced reclaimed shot. Starting with a clean, cold barrel, I fired 3 fouling shots before shooting for score. The result:


The stats for enhanced reclaimed shot updated to include the do-over for group #1:


You may recall that there was a problem with fierce mirage on the day I tested air-cooled Lyman #2. At the time I did not feel that the mirage was to blame for Lyman #2's poor results, but just to be fair I set out to completely re-test air-cooled Lyman #2. Range conditions were 20 degrees F, dead calm, sunny, and mild mirage causing the aiming point to jiggle 1/4" to and fro (it's a rare day when there is zero mirage at my range). Yet accuracy was not one iota better than the original test, so I abandoned the re-test after 50 rounds, and will stand by the original data for Lyman #2.


In the original test with air-cooled Lyman #2, there was leading in the corners of the grooves near the muzzle. But this time I could not find any leading. Apparently whatever caused the poor accuracy was not leading.


I had toyed with including air-cooled wheelweight in the shootout, but after Lyman #2's poor results I could not see any point in trying an even softer alloy. There just aren't that many alloys suitable for high velocity cast, so I'm going to wrap up this shootout and move on to other projects.

Summary for all alloys, including the revised data for enhanced reclaimed shot:


Conclusions
J.R. reclaimed shot and enhanced reclaimed shot tied for best alloy. Either there is no improvement in accuracy above 35 BHN, or if there is an improvement it is so small that I am unable to detect it with this 1.5 MOA load. Either way, reclaimed shot gets the nod to be my pet alloy for gas checked high velocity cast.

Linotype was not far behind.

Oven treated Lyman #2 was no harder than air-cooled Lyman #2, yet somehow it equaled linotype for accuracy. Perhaps there is a logical explanation, but I can't tell you what it might be.

Air-cooled Lyman #2 performed poorly. I bent over backwards to give Lyman #2 a chance to prove itself, but it just wasn't up to the job.

With it's favorite alloy this load proved it could consistently average 1.5 MOA ten shot groups at 3180 fps and 163,000 rpm and 50+ksi, using a relatively fast burning powder. That is impressive performance for an uncoated, unpatched cast bullet.

[mtngun]

Update: I was bothered by the contradictions from the heat treated Lyman #2 test, so I heat treated another batch of Lyman #2 samples and will be re-testing their BHN:

-- after 1 day, 28.6 BHN with 10mm / 150 kg test, 25.2 BHN with 4mm / 60lb test.
-- after 5 days, 29 BHN with 10mm / 150 kg, 25.6 BHN with 4mm / 60lb.
-- after 8 days, 29.7 BHN with 10mm/ 150 kg, 27.3 BHN with 4mm / 60lb.
-- after 2 weeks, 27.2 BHN with 10mm/ 150 kg, 22.7 BHN with 4mm / 60lb.

OK, so this batch definitely hardened. Why then did I measure 14-18 BHN on the day of the shooting test?

It's always possible that my original hardness test was a booboo, but that's tough to believe considering that I typically take one measurement with the 10mm test and three measurements with the 4mm test -- did I booboo on all 4 measurements? On the other hand, it's possible that I when I went to do the BHN test, I mistakenly grabbed an air-cooled slug rather than a heat treated slug.

I didn't record how long the bullets had aged before I shot them on December 10, but from memory they had aged about 2 weeks, so let's see how hard these new samples are after 2 weeks and re-evaluate the situation then, OK?

UPDATE: I've decided that I must have mistakenly grabbed an air-cooled slug when I did the original BHN test for heat-treated Lyman #2. But, to eliminate any doubt, I will simply redo the entire shooting & BHN test for heat-treated Lyman #2.

[mtngun]

OK, I retested oven-treated Lyman #2. On the day of the test the bullets had aged 5 days and measured 25.6 - 29 BHN. So far, so good.

But .... on the day of the test it was cold and sunny and there was lots of mirage inside my shooting muffler. The target was jiggling 3/8" to and fro and the image was so fuzzy that I could not clearly make out the aiming points, hence I had to outline the target square with a sharpie. Most of the groups were terrible.

Due to the mirage, I feel that this target was not representative of the load's capabilities, so I will disregard this target.


I haven't decided whether to attempt yet a third do-over of oven treated Lyman #2. In hindsight, I suspect the only problem with the original test was that I must have mistakenly grabbed an air-cooled bullet for the BHN test. I'm kinda bummed right now so I'm going to let this project sit for a while until I get some more inspiration.