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CBA loads - Page 6 - Mountain Molds

CBA loads

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Re: CBA loads

Postby mtngun » Sun Jul 02, 2017 7:01 am

Testing slow powders, to see if reducing the pressure and acceleration will help accuracy.

I've decided that rather than using the barrel's most accurate bullet (the ULR or PLR) as my control load, I will instead use a bullet has shown potential but always had a couple of fliers spoiling its groups -- the 193 gr. Loverider. The 193 has typically put 8 shots in a decent group with 2 low shots spoiling accuracy. Since its velocity variation has been good, I suspect that the 193's low fliers are due to the heavy bullet's increased pressure causing some sort of deformation or damage. Let's see if reducing the pressure makes the 193's low fliers go away?

Before shooting I had JB'd the barrel to get it squeaky clean, then the barrel was cleaned between groups with a brush and Seafoam. Lately most fouling shots have been landing within the group so I did not bother to load a fouling shot today. Naturally, today's fouling shot's landed outside the group :twisted:, so I only counted 9 shots.

The control load with IMR 8208 was true to form with 7 shots in less than an inch but 2 low fliers spoiling the group.

IMR4350 shot one ragged hole. I was impressed. Even using a drop tube, this was a heavily compressed powder charge and velocity was only 2166 fps.

WW760 made a shotgun pattern. WW760 has always been a finicky cast bullet powder for me, shooting well in a few cartridges but poorly in others, with no rhyme or reason.
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Was IMR4350's improved accuracy due to the lower pressure and lower acceleration, or due to the lower velocity? I vote for pressure and acceleration, but there is no way to know for sure.
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IMR4350 left dark carbon streaks. The thin shiny streaks in the corners of the groove might be lead, though I can't be positive. Overall IMR4350 was "average" for cleanliness.

WW760 was cleaner than average, but the thin shiny streak in the corner of the groove might be lead, though I can't be positive.

IMR8208 left a thin grey haze but otherwise was pretty clean. The thin shiny streak in the corner of the groove might be lead, though I can't be positive.
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The first shot of the day lost a gas check. It landed outside the group, but then again it was a fouling shot, and it is common for fouling shots to land outside the group.
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Conclusions:
-- the nice group with IMR4350 seemed to reinforce my theory that I need to reduce pressure and acceleration. Then again, the lousy group with WW760 does not reinforce that theory. :roll:

-- all of today's loads left a thin shiny streak in the corner of the grooves that might be leading. If so it's not bad leading, but then again there's no such thing as good leading. Any leading or any hard carbon fouling will deform the next bullet that passes over it. I'm puzzled as to why this Shilen is leading at 40 - 50 ksi while my Pacnor 7BR doesn't lead at 60 ksi? Maybe I just got lucky with the $90 Pacnor?

-- I'm still leaning toward punching the Shilen's chamber out to 308 Winchester, but I want to think about it some more.

-- the alternative is to lower the 30BR's velocity down to 2150 fps, but that would defeat the whole purpose of using a 14" twist in CBA competition. The idea behind the 14" twist is to allow the velocity to be increased to 2300 for less wind drift.

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Re: CBA loads

Postby mtngun » Mon Jul 03, 2017 7:12 am

To further test the theory that high pressure and high acceleration are limiting accuracy, today I tried reducing the charge of IMR8208. Of course that reduces velocity, too.

I was aiming for 2150 fps but mis-guessed the powder charge and ended up with 2218 fps. Oh well, it's still useful data. Even at 2218 fps, accuracy was the best the 193 has ever done, even counting the 11th shot low flier.
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I've decided to proceed with punching the chamber out to 308 Winchester. I'm not 100% sure my theory is correct, but I don't have any better ideas at the moment and the important thing is to keep moving forward and keep learning.

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Re: CBA loads

Postby mtngun » Sat Jul 08, 2017 1:23 pm

Lately I have been seating gas checks in a . I'm not sure that the seating step makes any difference but it provides peace of mind because I KNOW that every gas check was firmly seated.
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Re: CBA loads

Postby mtngun » Sat Jul 08, 2017 6:21 pm

OK, I ran the 30BR reamer in deeper until the bolt would close on a 308 Winchester "Go" gage. The neck was reamed with the same 0.331" reamer as before but actually came out 0.332" (reamers often cut oversize). The throat was reamed with the same 1/2 degree per side reamer as before and I tried to make it the same length as before, too. The entrance to the throat is 0.309", which might be a hair fatter than the 30BR's throat.

The 30BR has a steeper shoulder angle than a 308 Winchester, plus my 30BR reamer has minimal body taper, so in essence the new chamber is a 308 Improved. I only did that because I was too lazy to make a 308W reamer, not for any performance reasons. :lol:
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Today I shot 6 rounds to check the powder charge and basic functioning. The velocity was a bit too fast so I'll have to adjust the powder charge. More importantly I had mis-guessed the neck thickness and consequently the loaded necks were 0.333" - 0.334" -- not cool in a 0.332" chamber neck! :shock: I had to use gorilla force to close the bolt on the too-tight necks. Not surprisingly, accuracy was lousy.

I'll re-turn the necks and give H414 another chance to prove itself. Then I have a list of other powders that I want to try. I suspect this cartridge will be picky about powder due to the low pressures and low (75 - 80%) powder fill density.
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Re: CBA loads

Postby mtngun » Sun Jul 09, 2017 5:18 pm

Some of the Quickload data I'm looking at for the 308 Win and the 193 gr. bullet, listed from highest pressure to lowest pressure. Obviously Quickload is not always right so these numbers should not be viewed as gospel.

Further, many of the powders that look great in Quickload will fail in real life because they will not burn well at these reduced pressures.

Nonetheless, the Quickload data shows what is theoretically possible *if* I can find a powder that is happy under these circumstances. In theory, I may be able to reduce the pressure and the acceleration by one third while maintaining the same 2300 fps velocity. 8-) It's just an experiment and it may or may not work.
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Re: CBA loads

Postby mtngun » Sun Jul 09, 2017 5:35 pm

Last time the case necks were too tight in the chamber so I re-turned all the necks, aiming for 0.0110" - 0.0115" thickness. In theory that will allow the cartridge neck to fit in the 0.332" chamber neck with a bullet diameter up to 0.309".

By the way, somewhere along the way I picked up a Shars tubing micrometer on ebay. Even though it is Chinese, it works fine.
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When loaded with a 0.3084" bullet, there is 0.0001" clearance. Well, as machinists like to say, "CLEARANCE IS CLEARANCE!" :lol: Seriously, I'll have to keep an eye on the necks and maybe turn them a smidge more if I notice chambering resistance.
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Re: CBA loads

Postby mtngun » Sun Jul 09, 2017 8:45 pm

Beginning the search for Mr. Happy Powder in the 308 chamber. :lol: The usual procedure of cleaning in between groups and then firing one fouling shot -- if the fouling shot lands inside the main group it is counted, if it lands outside the main group it is ignored.

H414's ES of 50 was better than I expected, and the bore looked decent, too.
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RL19 had a not-so-great ES of 63, and left a uniform brown-grey haze in the bore. However bear in mind that this photo was taken 12" from the muzzle while the worst carbon accumulation takes place at the breach end. In fact there was a lot of caked on carbon at the breach end, enough that I had a hard time cleaning it. Even after brushing with Seafoam I could still feel resistance with a snug patch, and the patches were coming out with shiny hard carbon cake.
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RL15 had a lousy ES of 82 and a uniform brown-grey haze. I could feel resistance as I attempted to clean the breach end of the barrel, and even after scrubbing for several minutes I was still getting shiny hard carbon cake on the patches. In the end I gave up scrubbing and instead wetted the bore with Seafoam, will let the Seafoam attack the carbon overnight, and will try scrubbing again tomorrow.
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All of today's powders made shotgun patterns. H414 at least tried to shoot a group, but RL19 and RL15 were totally random -- perhaps due to their hard carbon fouling.

These results were very disappointing, but I anticipated that it might be tricky to find a powder that would burn well at low pressure. There are still quite a few powders to try.
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2 cases lost their necks today -- apparently I turned the necks a little too close to the shoulder. Oops! :oops: If I decide to keep this chamber I may scrap this batch of cases and start over.
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Re: CBA loads

Postby mtngun » Mon Jul 10, 2017 8:37 pm

Update on cleaning the carbon: after giving the Seafoam 24 hours to work on the carbon, I brushed and swabbed some more. The patches were still coming out black and with some shiny dark stuff. So once again I wetted the barrel with Seafoam and will let it sit for another 24 hours and try again. To think that all that fouling was created by only 11 shots! :o Geesh.

The difference between using RL15 in a full throttle jacketed load vs. a half throttle cast load is the powder burns cleaner at higher pressure and to some extent a jacketed bullet can scrape carbon out of the barrel and maintain a consistent bore condition, whereas a cast bullet will be abraded by carbon fouling and fouling may continue to accumulate.

A random thought -- these 180 - 190 gr. bullets seem more sensitive to pressure than the light bullets I typically use for hi-vel loads. I'm wondering if the longer bullets are more apt to bend and become banana shaped when "slapped" by pressure? If so then perhaps the long bullets would benefit from a harder alloy? I would like to do an alloy shootout in this barrel once I settle on a control load.

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Re: CBA loads

Postby mtngun » Wed Jul 12, 2017 8:54 am

Continuing the search for Mr. Happy Powder in the 308 chamber. All of today's loads used the usual 193 gr. Loverider at the usual 35 BHN.

The usual borescope photos 12 inches from the muzzle, taken with a camera looking through my Russian borescope. While better than nothing, these muzzle-end views don't do justice to the carbon fouling problem because if there's going to be a serious carbon fouling problem, it'll be at the breach end.

IMR4350 at 2319 fps and ~38,000 psi. Some carbon and perhaps some lead in the corners of the grooves, nonetheless it cleaned up easily.
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H4895 at 2403 fps and ~42,000 psi. It doesn't look so bad at this location, but I suspect the breach end was very dirty judging by the difficulty of cleaning.
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Accurate 2520 at 2447 fps and ~44,000 psi. Definitely some leading in the corner of the groove, and it was difficult to clean.
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IMR4350 and AC2520 at least tried to shoot a group, while H4895 made a shotgun pattern.

Velocities with H4895 and AC2520 were higher than intended, but in my mind that cannot excuse the poor accuracy. I mean, if my 7BR can average 1.25" at 3000 fps without cleaning the barrel, why should this barrel get a pass at 2400 fps?
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H4895 has a reputation for being a good powder in half throttle cast loads, so I was surprised that it failed in this test.

There are still some more powders I would like to try, and perhaps I will retest AC2520 and try to get its velocity right.

My take so far is that this chamber/barrel combination is a dog. Perhaps I will eventually find a powder that makes it perk up, but just the fact that it is so picky suggests that something is wrong. Carbon fouling is definitely one problem, but why does this barrel carbon foul so much more than my other barrels? Perhaps the barrel is a lemon, yet in 30BR form it could average 1 MOA as long as I didn't push it too fast, and that's similar to what most CBA competitors are getting with their 30BRs.

I wonder if there is some problem that I am overlooking?

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Re: CBA loads

Postby mtngun » Fri Jul 14, 2017 1:32 pm

I unscrewed the barrel so that the breach end could be inspected with a borescope. The last load fired was Accurate 2520 and it was fairly dirty. Then the barrel had been cleaned with my usual routine of a brass brush and Seafoam, followed by a patch and Seafoam.

Very little carbon remained that I could see, but there was definitely leading next to one particular land in the leade. Remember, this is after routine cleaning.
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This view shows the beginning of the leading. It seems to start with some scuffing at the entrance to the throat. I was looking for a burr that might be responsible, but could not identify any such thing.
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There was also some slight leading in the corners of the grooves about 8" from the breach. The routine brushing had not removed this.
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I tried some Birchwood Casey lead remover cloth. So far it has not made much improvement to the leaded spots, but it does do a good job of cleaning carbon. Even though I could not see carbon in the borescope, the Birchwood Casey cloth kept coming out black.
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Then I pushed an oiled pure lead slug back and forth through the barrel several times, trying to feel for a tight spot, but did not find one. FYI the resulting slug measured 0.3077".

In summary, the only problem I could find with the barrel was the one land that leaded in the leade area, but I could not determine the root cause of that leading. I'm debating what to do about it -- I might stick the barrel back in the lathe and spin the throating reamer a few times, not to cut the throat deeper but only to re-cut it at the existing depth, to clean up any possible uneven-ness.

The only other thing I can think of to address the one problem spot is to shoot a few more firelapping rounds. I hate to firelap a premium barrel that was already lapped at the factory, but firelapping is one way to clean up microscopic burrs that may have formed while reaming the throat.

In the meantime that one spot seems to accumulate leading and no bullet can pass over that spot without being deformed -- not cool. :evil:


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