CBA loads

[mtngun]

The alloy shootout resumes. Perfect range conditions. Every 10 shots the barrel was brushed, then one fouling shot was fired off-target.

Today I shot the oven treated JR shot & hard (not annealed) Gator checks. These were seated 2.698" COL which was "jam minus 10." Now if every group could have been like that 0.17" group, I would be content for a while.

Off topic, the top row averaged 2283 fps while the bottom row averaged 2246 fps. I've heard of some chronographs reading faster or slower depending on where the bullet passes over the chrono, but this was the first time I've clearly observed it.


4 days had passed since oven treating the bullets at 470F. BHN measured 30 using a 4mm ball & 25.8 kg load, or 39.6 using a 10mm ball & 149 kg load. It's normal for the 10mm test to report a higher BHN, but that's a bigger difference than usual. Nonetheless I checked my measurements and calculations and couldn't find anything wrong, so that's what I'm going with.

Here are the as-sized diameters of the bullet nose:
Front band -- 0.3013"
#9 (counting from the bottom) -- 0.3016"
#8 -- 0.3026"
#6 -- 0.3057"

EDIT: the barrel was cleaned every other group (every 10 shots). That means that 5 groups were fired with a clean barrel (0.73", 0.90", 0.17", 0.79", 0.69") and 5 groups were fired with a relatively dirty barrel (0.60", 0.50", 0.60", 0.39", 0.72"). The clean groups averaged 0.66" while the dirty groups averaged 0.56".

[mtngun]

Perfect range conditions for testing "enhanced" reclaimed shot & hard gas checks.

This alloy was made by adding one tablespoon of sulfur to 10 pounds J.R. brand reclaimed shot, then adding 0.8 pounds of Rotometals 30% antimony. A previous batch increased BHN 6 to 8 points, but today, after aging for 5 days, it tested 29.8 BHN with a 4mm test and 39.7 BHN with a 10mm test -- essentially the same as regular J.R. brand reclaimed shot.

EDIT: after aging 12 days, it scored 38.2 on the 10mm test and 33.1 on the 4mm test, still about the same as regular reclaimed shot.

Nonetheless, it was harder on the day I nose sized it, and the noses sprang back more than J.R. shot.
front band = 0.3015"
band #9 = 0.3015"
band #8 = 0.3025"
band #6 = 0.3060"

Due to the fatter noses, the jam point was different than J.R. shot, so I ended up seating these bullets 0.017" deeper at 2.681" instead of 2.689". However, bear in mind that if you measure the jam with 10 different bullets, you get 10 different results because there is "feel" involved. I actually measured jam with 2 bullets, one was 2.672" and the other 2.715", for an average of 2.689" jam. But what if the 2.715" was right and the 2.672" was wrong?

Weight was 201.8 gr., nearly the same as regular J.R. shot.

Accuracy was definitely inferior to regular J.R. shot. However, since the weight was practically the same and since the BHN was practically the same, how do you explain the difference in accuracy? In hindsight, I wonder if it was due to the 0.017" deeper seating depth?

I started out cleaning every other group, but noticed that the group immediately after cleaning was less accurate even though one fouling shot was fired, so then I postponed cleaning until a group seemed to open up. The 4 groups fired immediately after cleaning averaged 1.05" while the 6 "dirty" groups averaged 0.68". Yesterday's groups averaged 0.66" for the 5 clean groups and 0.56" for the 5 dirty groups. In both cases, the dirty groups were on average better than the clean groups. Hmmm.


Today's test with "enhanced" reclaimed shot raises several questions:
-- why wasn't it harder? Age? Normal lot-to-lot and bullet-to-bullet variation?
-- why was it less accurate? That may be due to the deeper seating depth. Besides the fact that the jam point measurement is not highly repeatable, the "jam minus 10" setting was something that was decided on for the Shilen barrel but has never been verified in this Hart barrel, which engraves the nose differently.
-- is my cleaning routine optimal? The Shilen barrel carbon-fouled like a son-of-a-gun, was most accurate when squeaky clean, and only needed one fouling shot if even that, but I'm learning that this Hart barrel has a different personality.

No matter how hard I try to make my shootouts apples-to-apples, Mr. Murphy never fails to throw in some oranges and bananas. It's frustrating, but as long as I'm learning stuff that's the important thing.

[mtngun]

Continuing the alloy shootout, today with the same oven treated J.R. brand reclaimed shot tested previously except this time with annealed gas checks.

Even though there has been evidence that my every-other-group cleaning routine may not be optimal, I decided to stick with it for the duration of this shootout so the test will be apples-to-apples. Since the last test with "enhanced" reclaimed shot suggested that seating depth might be critical, I seated today's bullets to 2.699" COL which is "jam minus 9." The control load used 2.698" and the 0.001" discrepancy is just normal variation -- my homemade seating die is not micrometer adjustable and the measurements vary from bullet to bullet anyway because you're measuring on the sharp point, so if I can get within 0.001" that's good.

Good range conditions today.

The annealed checks averaged 0.88" vs. 0.61" for hard checks. A student's t-test says that is statistically significant, so don't anneal your gas checks.


I've been shooting annealed checks for most of this year thinking it might help with the flying check problem. Well, it didn't make an iota of difference with the flying check problem (what has made a difference is good chamber design and seating checks on a seater prior to sizing) so about a month ago I switched to hard gas checks and accuracy seemed to improve. Today's test seems to confirm that hard gas checks are better. Annealed gas checks seems to be another one of those old wives tales that is often stated as an undisputed fact, yet nobody seems to have any data to back it up. Well, now there is data on the subject.

Why might a hard gas check be more accurate? Well, if the job of a gas check is to act as a scraper, then a hard check might be a more effective scraper than a soft check. If the job of a gas check is to prevent the base from deforming, then a hard check might resist deformation better than a soft check. If the job of a gas check is to protect the base from being melted by hot gases, then both hard & soft checks should do that equally well. I can't think of any reason that a soft check would perform better??? Yes, annealed brass can "grip" better than fatigued brass, but gas checks are not necessarily fatigued as they come from the factory, and I haven't seen any evidence that annealing affects the flying gas check problem.

The 5 groups shot after cleaning averaged 0.83" vs. 0.93" for the 5 "dirty" groups.

You can't tell from the photo but I started this shootout high up on the target and have been gradually shooting my way down the target. The chrono seems to read lower velocities as you go down the target, but I'll try to confirm that in the near future.

Having aged for 9 days, today's bullets scored 39 BHN on the 10mm test and 34.8 BHN on the 4mm test -- pretty much what I've come to expect from this lot of reclaimed shot.

[mtngun]

The alloy shootout continues with linotype & hard Gator checks.

The relatively soft linotype bullets didn't spring back as much in the nose die so their nose diameters were a tiny bit smaller and hence their jam COL was longer. They jammed hard at 2.727" so I seated them 2.717" for "jam minus 10."

I did not expect linotype to give first rate accuracy but nonetheless it is included in the shootout because it is the most common CBA alloy. As you can see, accuracy was just plain horrible from the get-go, nonetheless I went ahead and shot all 10 groups so there would be data to "prove" that accuracy was horrible. A t-test verified that lino's poor accuracy was statistically significant compared to the control load.

The 5 "clean" groups averaged 1.68" while the 5 "dirty" groups averaged 2.19". At the end of the day I borescoped the barrel and it was surprisingly clean -- zero leading, and only a little carbon. So I can't blame today's poor accuracy on fouling.


OK, but many CBA competitors use lino to shoot awesome groups, so what gives? For one thing the average CBA load is 36,000 psi while the load used in this test is 47,000 psi. That definitely makes a difference.

The other thing is that the Loverider design depends on a strong alloy to compensate for its minimal bearing area.

I'm not going to bother including softer alloys like Lyman #2 in this shootout because it's clear the Loverider needs a hard bullet. I would like to include an "extra hard" alloy and since my "enhanced reclaimed shot" was a dud this time around, I want to try again with one of my other "extra hard" alloys. It'll take me a while or so to cast & prep another batch of bullets and let them age to maximum hardness (usually around 1 week).

[mtngun]

After looking over my notes for various hard alloys, it appears that when tested with my current 10mm test, only one batch of one alloy -- "enhanced" J.R. shot -- hit 45 BHN (after aging 2 weeks). Unfortunately, my recent attempt to duplicate that one batch failed for unknown reasons.

That leaves me with no alloy much harder than 40 BHN. Well, some of my other batches of reclaimed shot peaked at 42 BHN, but that's not a big enough difference to justify including in the alloy shootout.

I think I will try adding more Rotometals Superhard to my "enhanced" J.R. shot and see if that will get it up to 45 BHN. If not, then this alloy shootout is finished, and I'll post a wrap up later. Even though I am quite fond of COWW, I did not include it in this shootout because it is becoming difficult to find in some parts of the country.

[mtngun]

I cast and loaded some DERS bullets that had been quenched in ice water, optimistic that they would reach my goal of 45 BHN. As it turned out, they were no harder than bullets quenched in room temperature water. Nonetheless, since they were already loaded I might as well shoot them.

The weather has been cold and stormy lately. I waited for what appeared to be a calm morning. It was 40 degrees F outside but 60 - 65 F inside the shack. At first it was calm, but by group #5 the wind had kicked in. It was only 5 - 10 mph, but it changed direction several times a second, making wind doping nearly impossible. In hindsight I should not have attempted to shoot today, but you can't be sure until you try it, and there was no better weather in the forecast, and winter is knocking at the door.

The usual procedure of cleaning every 10 shots, then firing one fouling shot off the target.

Bullets were seated 2.699", which is approximately "jam minus 10."

The ice water quenched DERS alloy measured 40.3 BHN today after aging for 2 weeks -- that's not significantly different than the 39 BHN of the J.R. brand reclaimed shot used as a control load, so I did not expect a significant improvement in accuracy.

The DERS bullets averaged 0.89", worse than the control load.

"Clean" groups averaged 0.88" while "Dirty" groups averaged 0.90", not a significant difference.

Groups #1 - #5, shot under calm conditions, averaged 0.79" while groups #6 - #10, shot under windy conditions, averaged 0.99".

The 0.79" figure is more representative of what the DERS bullet can do under good range conditions, yet it is still less accurate than the control load, so the 40.3 BHN DERS bullet was actually less accurate than the 39 BHN control load.


OK, so the ice water quenched DERS alloy was a failure in the sense that it was only 2 BHN harder than ordinary reclaimed shot at a given age. But that trivial difference in BHN does not explain why they were less accurate than the control bullets, does it?

Besides the tiny difference in BHN, there was also a difference in density and a difference in diameter. The DERS bullets weighed 199.5 gr. vs. 202+ grains for the control bullets. You wouldn't think that would be significant, but it can change the bullet's dynamic balance, so that's one possible explanation for the poor accuracy.

The DERS bullets dropped out of the mold a little fatter than the control alloy. They received the same sizing procedures as the control alloy, however the bore riding bands do not get sized, so perhaps that is a factor? I have never done any optimization experiments for the diameter of the bore riding bands on Loverider bullets, so that may be the next thing to test.

That concludes the alloy shootout. Ordinary reclaimed shot with hard gas checks performed the best.

It's looking like my part of the country may have another hard winter. If that's the case then I may not get much more serious rifle shooting done until spring. When range conditions allow I'll try to do a test with different bore riding band diameters. Should the bore riding bands be a slip fit, or should they engrave slightly?