CBA loads

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mtngun
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Re: CBA loads

Postby mtngun » Sat Aug 12, 2017 8:38 am

While the jury is still out on the 31.0 gr N135 & 198 gr. load, so far it seems willing to shoot 0.80" - 1.05", maybe better if range conditions would cooperate long enough to finish dialing in the load. :lol:

So I checked the load's estimated pressure in Quickload using common IMR & Hodgdon powders (because Quickload doesn't seem to have good handle on N135). Anyway, the 31.0 gr. load produces pressure and acceleration close to CBA averages.
Image

If pressure and acceleration are limiting factors because they deform the bullet, then it may be possible to reduce the deformation by tweaking the bullet design or by using a stronger alloy. I'll explore that possibility in due time.

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Re: CBA loads

Postby mtngun » Sat Aug 12, 2017 7:08 pm

I finished testing the 198 gr. bullet / 31.0 N135 combo this evening (the lower two targets in the photo). The previous 3 targets were photoshopped into the top row so you can see all 5 targets without looking back through previous posts.

When all the dust was settled, the 198 / 31.0 load averaged 1.00" for 5 groups vs. the 193 / 33.2 control load averaged 0.98" for 4 groups. That's not a significant difference, so this barrel is still stuck at 1 MOA no matter what I do. :lol:

For what it's worth J-10 and J-6 came out on top, but the small differences in accuracy could be due to random variation rather than due to the jam setting.
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As always, there are more tweaks that could be done and should be done to optimize this load's accuracy, but my priority at the moment is bullet design so I'm going to move on to tweaking the 198 gr. bullet by re-cutting its bottom band to be a groove diameter band.

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Re: CBA loads

Postby mtngun » Wed Aug 16, 2017 9:44 pm

I recut the 198 gr. Loverider as shown. It gained weight in the process so now it is the 199 gr. Loverider.

In general, the idea behind a Loverider is to minimize distortion when the bullet engraves. The question then becomes "how much engraving is optimal?" There is no obvious answer, so let's try different things and see which shoots best.
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There was some intermittent light mirage and an intermittent 5 - 10 mph wind. Accuracy so far is not as good as the 198 gr. version, but range conditions or random variation might be at play, so I will try again on another day before I reach a verdict on the 199 grainer.
Image

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Re: CBA loads

Postby mtngun » Thu Aug 17, 2017 8:46 am

Behind the bench at 6 a.m., no wind and no mirage. 8-)

Perhaps due to the good range conditions, groups were better today, but no consistent.
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So far there is no evidence that the 199 grainer is better than the 198 grainer, and some evidence that the 199 may be worse, however I want to shoot a few more groups before I make up my mind. Let's see if the 32.0 gr. load is repeatable.

FYI I tried using only a wet patch because I've been having problems with one brand of brass brush shedding its bristles. The bristles then get left behind in the chamber or throat and cause problems. Unfortunately a wet patch is not enough to get all the carbon out, so I went back to brushing between groups, only with a different brand of brush.

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Re: CBA loads

Postby mtngun » Fri Aug 18, 2017 8:22 am

Re-testing the 199 gr. Loverider with the 32.0 gr. N135 charge, which shot a 0.80" group yesterday. The group on the top left is yesterday's group, while the other three groups on the top row were shot today.

The 198 gr. target is photoshopped into the lower half of the image so you can compare targets without having to look back through old posts.

My observations:
-- the 199 was less accurate than the 198 with the 31.0 gr. charge
-- but when the charge was tweaked to 32.0 gr., then the 199 was equally accurate.
-- the 198 always put fouling shots into the main group, but the 199 often spit fouling shots out of the main group.
-- you could say that the overall performance was equal. The 199 was definitely not superior to the 198.
Image

Yesterday's loads were seated 2.704", which I thought at the time was Jam minus 10. However, I had never actually measured the jam point with the 199, instead I just assumed that it was the same 2.714" as the 198, since they were nose sized the same. But then I measured the jam with three different bullets and got 2.678", 2.699", and 2.727", for an average of 2.701". Which is correct? They are all correct! The variation is due to how hard you push the bullet into the rifling. My habit is to push with "moderate thumb pressure," but since my thumb is not a calibrated instrument, sometimes I probably push harder than other times.

An alternative method would be to seat a bullet long in a dummy case, then let it "self-seat" as the dummy is chambered. However then the results would vary with neck tension, hence I went with the "thumb pressure" method.

Well if you believe that the Jam point is 2.701", then yesterday's loads at 2.704" were Jam plus 3, not Jam minus 10 as I said at the time. Today's loads were seated 2.694" making them Jam minus 7. At any rate, it didn't seem to change the accuracy. In general I've gotten best accuracy either right at Jam or 5 to 10 away from Jam.

EDIT: I forgot to mention that I had JB'd the barrel prior to today's session. My thinking was that every time I have JB'd this barrel, the next group was a good group. And that was true today with the 9 in 0.85" group. Maybe I should JB once a day?

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Re: CBA loads

Postby mtngun » Fri Aug 18, 2017 5:36 pm

The 199's G1 BC = 0.301" when launched at 2227 fps.

There was a gentle breeze while I was shooting the BC and both horizontal fliers were due to me not doping the wind correctly. Oh well, that's part of the game.
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Image

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Re: CBA loads

Postby mtngun » Sun Aug 20, 2017 6:00 am

I took the lessons learned from the 198 - 199 gr. bullet and applied them to a nominal 200 grain bullet. It actually weighs 202 - 203 grains ready to shoot when cast of J.R. brand reclaimed shot.

The Miller Stability factor with this bad boy is only 1.25 when launched 2200 fps at sea level, so it's violating my self-imposed minimum of 1.3. I don't anticipate any problems, though.
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The group on the left was shot with a flashlight illuminating the target in the pre-dawn light. The flashlight worked well enough but the fouling shot took out my aiming point. For the next group I adjusted the scope so that my aiming point would not get shot up. :lol:

This bullet looks to be a keeper other than the high ES. Next time I'll try tweaking the jam to see if that can improve the ES.
Image

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Re: CBA loads

Postby mtngun » Tue Aug 22, 2017 8:47 am

Today I attempted to re-test the 33.2 gr. N135 & 202 gr. Loverider combo that shot well last time. Plus, I tweaked the COL.

The 2.700" COL group was shot by flashlight at 5:30 a.m.. Unfortunately there was some boiling mirage. It's hard to judge how much mirage hurts accuracy -- some days I have been able to shoot good groups in mirage while other days it is a lost cause. Well, this time it was a lost cause. I will disregard this target and re-test the 2.700" COL under better range conditions.

The 2.694" and 2.689" COL groups were shot about 30 minutes later. By then the flashlight was no longer needed and most of the mirage was gone.

I was brushing between groups and not shooting a separate fouling shots. That has worked OK with some bullets, but it does not seem to work with this 202 grainer. OK, from now on I will load 11 rounds with this bullet so the fouler can be dismissed and still leave 10 shots.
Image

Conclusion:
-- I'll have to re-test the 2.700" COL under better range conditions
-- otherwise, it didn't seem like the changes in COL made much difference, which is good.
-- all of today's groups had decent ES

Once I settle on a COL, I want to use that load as a control for an alloy shootout. As always, there are other load tweaks that could and should be done to improve accuracy, but one thing at a time.

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Re: CBA loads

Postby mtngun » Wed Aug 23, 2017 6:40 am

Here's a re-test of the 202 grainer at 2.700" COL, which is about Jam minus 10. I fired a fouling shot off-target before shooting the group.

The first 9 shots went into 0.85", then the 10th shot opened it up to 1.12". It has been my experience that I'll often have a good group going until shots #7 - 10, then that's when the fliers happen, perhaps due to carbon fouling?

At any rate, the 202 seems to average 1 inch, so I'm still stuck at 1 inch. I have progressed in the sense that I'm now able to do one inch with a heavier, more wind resistant bullet at a respectable 2280 fps, but darned if I can break through that 1 inch barrier. Ten shot sub-MOA with cast is hard! :o
Image

My current theory is that the two main obstacles to accuracy with these loads -- besides range conditions -- are 1) deformation due to pressure & acceleration and 2) deformation due to carbon fouling. One of these days I would like to experiment with cleaning the barrel after every other shot (shoot one fouling shot, one shot on target, then clean and repeat) to see if that eliminates the fliers?

Up Next:
-- test the 202's BC.
-- do an alloy shootout with the 202. If my deformation theory is valid, then a harder alloy ought to reduce deformation.
-- try the 202 with IMR4350 and N140. They're slower than N135 so they might reduce deformation, if I can get them to burn decent.

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Re: CBA loads

Postby mtngun » Thu Aug 24, 2017 7:28 am

Briefly testing a 203 gr. Loverider. The mold for this 203 will be donated as a prize for the 2017 CBA nationals. It has some minor design tweaks compared to the 202 grainer that I shot last time.

The barrel had been JB'd and one fouling shot was fired off-target prior to shooting the group.

It scored a low 0.247" BC when launched at 2287 fps from the 14" twist. That seems strange considering that the nearly identical 199 gr. Loverider scored a 0.301" BC? At 1.28" long, the 203's Miller Stability Factor is 1.47" at my 4600 foot elevation, but its low BC suggests that it might be yawing?

Nonetheless I love the way it yawed 10 shots into 0.600" at 100 yards! 8-) 8-) 8-)

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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FYI the COL happened to be 2.709" and the jam happened to be Jam minus 24. That was not a deliberate choice, it's just that out of laziness I left the die settings where they were and that's how it ended up. :lol:

And ... these bullets used non-annealed gas checks. Prior to this I had been using annealed gas checks. The annealed gas checks date back to when I was having problems with checks coming off in flight, however annealing failed to fix that, so as the annealed checks are used up they are being replaced with non-annealed checks. I never did an accuracy shoot-out with annealed vs. non-annealed, but it's conceivable that the non-annealed checks may be more accurate because they are harder and more resistant to deformation.


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