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.
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.
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.