CBA loads

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Re: CBA loads

Postby mtngun » Fri Aug 25, 2017 8:11 am

Trying a couple of different powders with the 202 gr. Loverider, and testing BCs. I doubt if I will find a better powder than N135, but you can't blame a guy for trying.

I had tested IMR4350 once before with 38.0 gr., but it burned dirty, so today I upped the charge to 39.0 gr.. It did a little better but the 46 ES was still higher than I like and it threw a flyer on shot #8. While I did not take time to borescope the barrel afterwards, there was a lot of drag on the cleaning rod, suggesting that it had hard fouling. I'm inclined to give up on IMR4350 -- it doesn't seem to generate enough pressure to burn satisfactorily.

Since N135 has worked so well, I thought "why not try N140?" I started out with the same 33.2 gr. charge that I've been using for N135. Velocity was about 100 fps slower than N135, and the 48 ES was higher than I like, but accuracy was decent. There was not much drag on the cleaning rod.

As for the BC, either the bullet is yawing when it leaves the muzzle or else the Shooting Chrony has drifted out of calibration. I doubt if there is anything wrong with the Shooting Chrony but I'll re-check its calibration against the Caldwell chrono when time allows.

UPDATE: I have since learned that my two chronographs are no longer in sync -- the Shooting Chrony used to read faster than the Caldwell, but when I tested them back to back today, the Shooting Chrony was reading slower, so the old correction factor no longer applies and I'll have to go back to the drawing board.
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Next Time:
-- check Chrony calibration
-- re-test N140 at 2300 fps

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Re: CBA loads

Postby mtngun » Sat Aug 26, 2017 8:23 am

Re-testing N140, this time cranking the velocity up to 2300 fps with the hope that it will burn a little better.

Accuracy was good, but the 48 ES is still higher than I would prefer. That darned shot #10 opened up the group. :x

By the way I checked the calibration of my two chronos and the Shooting Chrony appears to have drifted -- it used to read faster than the Caldwell, but today it read 1.2% slower. If I apply the 1.2% correction factor to today's results then the 202 grainer had a G1 BC = 0.297, which is a believable number (close to the SD). So I no longer believe that the 200+ grain bullets have a stabilization problem in this barrel. Yea! :)
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Before I discovered chrono problem, I filed down the tips on some 203 grainers to see if that would help stabilize them. Well, I no longer believe there was a stability problem, but nonetheless it's still useful data. If you assume that the original 203 had a BC = 0.300, then the small flat point subtracted about 0.020.
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Next Time:
-- now I have an excuse to buy a new chrono. :lol: I never liked the Shooting Chrony, anyway, with its very small sensor window.
-- the next big project is an alloy shootout. It'll take me a while to cast and prep the bullets.

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Re: CBA loads

Postby mtngun » Sat Sep 02, 2017 8:25 am

The alloy shootout has begun! :)

It will be five 10-shot groups with each alloy. Five groups will probably not be enough to prove a significant difference, unless one alloy is particularly awful, but I'm hoping it will be enough to show general trends. If the need arises, I can always go back and shoot more groups.

The load will be the 202 gr. Loverider with 35.5 gr. N140, seated 2.698" - 2.700" (it varies from one bullet to the next because you're measuring on the sharp point) which is approximately Jam minus 12, Federal #210 primer, and BAC lube. Gator checks are seated in a seater prior to sizing to 0.3085". Brushed between groups, then one fouling shot fired off target. From time to time I will also clean with JB because it seems to do a better job than brushing alone.

Today's alloy was J.R. reclaimed shot, oven treated at 470F, and non-annealed Gator checks. This will be the control load. Target #1 was shot on August 26 while targets #2 - #5 were shot today.

On target #3, I may have pulled the one flier. I was running out of breath and in a hurry to fire the shot before I turned blue. :lol: In hindsight I should have paused and taken a few breaths.

On target #5, the boiling mirage was starting to become a problem. It wasn't that bad, but I want to test alloys, not test my ability to shoot through mirage! :lol:

This load acts like it wants to shoot in the sevens when the range conditions are good and the guy behind the trigger does his part, but range conditions and human error are part of the game.
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Stats for J.R. reclaimed shot & non-annealed checks:
-- average 0.93" ten-shot group at 100 yards
-- average 2309 fps velocity
-- average 31 ES
-- 0.318 BC (using a Caldwell chrono at 15' and a Caldwell G2 downrange, and calibrating the G2 at the beginning of the day).
-- 31 BHN when measured with a 5/32" ball & 57 lb load. They had aged one day.

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Re: CBA loads

Postby mtngun » Mon Sep 04, 2017 8:47 am

I changed my mind :roll: and decided to use ten 5-shot groups for the alloy shootout, rather than five 10-shot groups, because 10 groups will give ten data points and that's often enough to prove a significant difference in accuracy. I'll have to retest the reclaimed shot & non-annealed checks.

In the meantime, here is reclaimed shot and annealed checks. These were shot at first light, which is usually the calmest time of day with the least mirage, but even so there was some intermittent mild mirage. I don't think the mirage was bad enough to hurt accuracy much, but you never can be sure.

At any rate accuracy was poor and this load certainly would not have won any CBA matches.
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Note that the BHN was a little softer than expected. They had aged 3 days since heat treating.

While conventional wisdom is that annealing gas checks is a good thing, this barrel has shot better groups with non-annealed checks. Maybe that's just a coincidence, but I can think of logical explanations. For one thing, to the extent that a gas check serves as a scraper, a hard check might be a more effective scraper than a soft check. That might be particularly important in this load due to its carbon fouling problem. Secondly, a hard check might be more resistant to deformation due to pressure. At any rate hopefully this shootout will eventually shed some light on the issue.

We've been having a heat wave which seems to make mirage impossible to avoid even at dawn, so I think I'm going to take a break from shooting until the heat wave has passed.

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Re: CBA loads

Postby mtngun » Wed Sep 06, 2017 7:00 am

Continuing the alloy shootout, this time with linotype and non-annealed gas checks. I started with a JB'd barrel, then brushed after every 10 shots on target, then fired one fouling shot off-target. Range conditions were mostly good.

Accuracy was horrible. :oops: The #'s indicate the order of firing. Group #1 was the best group, #2 was second best, and things went to hell after that. That suggests the barrel has a fouling problem and it wasn't getting clean with normal brushing.
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So .... at the end of the session I borescoped the barrel. This is after firing 6 shots since brushing, 8" from the breach, which is usually where the carbon fouling is worst. The photos are dark because the barrel is dark with carbon. But what is that line in the middle of the one groove? It's not supposed to be there! :o
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The line continued all the way back to the throat entrance. You can't see much detail because everything is dark with carbon.
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At other points along the entrance to the throat, there was some kind of fouling smeared on. I'm guessing it is lead but can't be certain. If it is lead then it suggests the bullet is shaving lead as it enters the throat. That would not be surprising. All the bullets in this shootout get the same sizing routine, however due to as-cast differences and springback differences, they don't end up with the same diameters. Today's lino bullets drop out of the mold bigger and that combined with springback leaves the base of the bullet at 0.309" instead of the usual 0.3085". The throat entrance is right at 0.309" so the fit may be too tight.
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I'll have to troubleshoot and fix the fouling problem before continuing the alloy shootout, and most likely I'll have to re-start the alloy shootout from scratch. That's frustrating but par for the course. That danged Mr. Murphy won't leave me alone! :twisted:

Meanwhile, I did suceed in measuring the BC of the lino bullets -- 0.311 when launched at 2350 fps. I expected the lino bullets to lose some BC due to them being less dense, but they didn't lose much, especially considering the velocity.

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Re: CBA loads

Postby mtngun » Wed Sep 06, 2017 1:55 pm

Doing detective work to understand why the barrel had fouled. :geek:

Yes, there is one deep scratch in the middle of one groove. This shows the start of the scratch (after brushing).
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The scratch follows the twist down the barrel. It's very consistent, almost like it was done with a machine. This is about mid-barrel. It peters out after about 16 or so inches. Well, the scratch certainly looks abnormal and it certainly makes me feel sad. :cry: It wasn't there the last time I borescoped the barrel, so I'm guessing that somewhere along the way a piece of hard grit got embedded in a bullet and created the scratch when the bullet traveled down the barrel. That said, I can't think of any reason the scratch would hurt accuracy or cause fouling.
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Most of the barrel cleaned up nicely with normal brushing, but there was this one spot at the leade that appeared to be a gob of lead.
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So then I cleaned with Birchwood Casey lead remover cloth, followed by a JB clean, until the glob was gone. It appears that the problem spot has pitting. Bear in mind that the Lyman borescope magnifies the image, so in real life the pits are microscopic. When viewed through my Russian borescope, the pits are barely visible. Nonetheless the pitting appears to be the root cause of the glob of lead. I could not identify anything else wrong other than the pitting.
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Recall that the previous chamber, the 308, had to be abandoned due mysterious damage at the leade. It wasn't clear if that damage was due to erosion or to something else, other than to say that one day the damage wasn't there and the next day it was there. :lol: Then I set the barrel back and cut this 30x1.75" chamber, but now it, too has damage at the leade, and this time it does appear to be pitting caused by erosion. I get the impression that the metal in the bore has fatigued such that it is prone to pit easily.

OPTIONS:
-- Set it back once again, but if my theory is correct then the new leade may be pitted after only a few hundred rounds.
-- Limp along with the pitted throat. Perhaps if I cleaned it aggressively after every group, the accuracy would be decent.
-- Scrap the Shilen and install a new barrel.

I do have another barrel on stand by, a Hart 14" twist, but it was intended for the homemade actions that I hope to build this winter. I'll have to think about this for a while before I make a decision.

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Re: CBA loads

Postby mtngun » Thu Sep 07, 2017 12:50 pm

I found more pitting in the Shilen, on one land. The pitting continued on this particular land for 2 or 3 inches. My verdict is this barrel is toast.
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The Shilen must have 3000+ rounds through it, most of them in the 40,000 - 50,000 psi range, so it does not owe me anything. RIP.
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Re: CBA loads

Postby mtngun » Sat Sep 09, 2017 1:08 pm

Goodbye Shilen, hello Hart.

The Hart came from a Kelby's clearance sale; I think I paid $155 or something like that. I'm guessing that Kelby's had scrapped it due to a shallow saw cut near the muzzle, because otherwise it's a good looking barrel. It's 6 groove, 14" twist, and has a benchrest taper so it's about 2 pounds lighter than the straight blank Shilen it replaces. The barrel length finished up at 26" and the rifle weighs 14 pounds, 3 ounces with the Weaver T36 scope.

The groove diameter seems to be spot on at 0.3080" while the bore, at a smidgen over 0.3000", is a few tenths tighter than the Shilen's,

I used the same reamers to cut the same 30x1.75" chamber, except I did run the 1/2 degree throating reamer in about 0.020" deeper. Since the specs are nearly identical to the Shilen's I'm hoping that load development will consist of nothing more than verfitying the new jam point. We'll see.
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Re: CBA loads

Postby mtngun » Sun Sep 10, 2017 6:52 am

Up at dawn for a trial run with the new Hart barrel. Perfect range conditions.

Even though I cut the throat 0.020" longer than the Shilen's, bullets had to be seated about 0.040" deeper. That's because the 0.3013" front band was engraving firmly in the Hart's 0.300"-ish bore. Whereas the Shilen engraved the nose uniformly, the Hart engraves the front band before the rest of the bullet makes contact. In other words, my nose die was a perfect match for the Shilen's throat, but doesn't size the front band enough for the Hart's throat. That's not necessarily a problem, though, so for the time being I'm not going to worry about it.

First I tried the linotype version of the 202 gr. Loverider, except it weights 193 gr. when cast of lino. Accuracy was poor so I did not bother shooting any more lino bullets.

Then I tried the reclaimed shot with hard gas check that had performed well in the Shilen. The reclaimed shot did much better than the lino, though a 0.99" five shot group is still nothing to brag about. I was nearly out of reclaimed shot bullets so I called it a day.

Velocities were a little higher than the Shilen. This was expected because the Hart's tighter bore increases the engraving pressure. I'm not opposed to more velocity as long as the load is accurate, but since accuracy is wanting I may be forced to dial back the powder charge.
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After 6 shots with the lino bullet, there was no leading anywhere. Whereas the lino bullet had leaded the Shilen's leade, the Hart's leade was squeaky clean. Cast bullets should not lead the barrel unless something is wrong.
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At the end of the session there was only a little carbon and no leading, so I did not bother brushing, instead merely cleaned with a patch wetted with Seafoam. The wet patch left the barrel squeaky clean.
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So the Hart's first day was a mix of good and bad. The bad news is that it doesn't particularly like this load. That may be simply due to excess velocity. I was hoping I could get away without any load development, but that was wishful thinking. At a minimum I need to tweak the powder charge to get the velocity down.

The good news is that there was no leading, only modest carbon fouling, and it cleaned up easily.

Already it is clear that reclaimed shot is superior to linotype in both barrels.

I'll have to cast & prep more bullets, so it may be a few days before I can proceed further. Once I have some bullets then I'll try different powder charges with N140 and N135, and hopefully find a satisfactory combination so I get back to the alloy shootout.

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Re: CBA loads

Postby mtngun » Sun Sep 17, 2017 12:03 pm

It took me a while to get bullets cast & prepped. I had originally planned to use the same nose sizing & seating setting for all alloys in the alloy shootout, but that wasn't working because the harder alloys were springing back more in the nose die. So I ended up using one nose die setting for linotype and another nose die setting for the heat treated alloys.

The jam point ended up being slightly different for each alloy. I was aiming for a 2.700" COL, which had worked well in the Shilen, but that wasn't always possible even with the tweaks to the nose die setting. I decided to stick with a "jam minus 10" seating depth, which will require a slightly different seating depth for each alloy.

Range conditions were breezy and miragy today so I held off on beginning the alloy shootout, and instead did a brief ladder test to dial in the powder charge. Five shots don't prove much, but for what it is worth accuracy was decent. I settled on 34.3 gr. N140, which gives about 2280 fps. Quickload believes that velocity generates 47,000 psi and 109,000 G's. The 47,000 psi pressure is higher than I would prefer, but reducing it to a more CBA-like 36,000 psi would drop the velocity to 2100 fps. :cry: It takes a big increase in pressure to produce a small increase in velocity.
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