CBA loads

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Re: CBA loads

Postby mtngun » Sat Apr 01, 2017 8:43 am

Back to selecting a powder .... I had narrowed it down to 3 semi-finalists, 8208, RL15, and LVR. Today I tried each of those powders with one group at 2100 fps, one group at 2200 fps, and one group at 2300 fps. All of today's loads used Rem 7 1/2 primers.

Not much difference in accuracy.
Image

Accuracy and velocity variation were usually best at 2300 fps. My original velocity goal was 2250 fps, just because that is a proven velocity & RPM for CBA competition, but the barrel seems to be saying that it prefers a little more velocity.
Image

Load Deets:
8208:
29.4 gr., 2125 fps, 102 ES
31.0 gr., 2232 fps, 74 ES
32.4 gr. 2295 fps, 63 ES

RL15:
31.0 gr., 2097 fps, 63 ES
32.4 gr., 2201 fps, 46 ES
33.9 gr., 2289 fps, 81 ES

Leverevolution (there is no Quickload data for this powder so I had to guess the charges and as a result the velocities were low)
30.3 gr., 2062 fps, 111 ES
32.0 gr., 2151 fps, 136 ES
33.4 gr., 2213 fps, 84 ES

Things to Try Next Time and Down The Road:
-- Retest 8208 and LVR at 2350 - 2400 fps.
-- perhaps try a magnum primer with LVR because it's a ball powder.
-- perhaps try shotgun buffer with LVR.

It looks like the 180 GC may shoot 1 MOA once I settle on a pet powder charge. 1 MOA is nice, but it's not nearly nice enough for CBA competition, where 1/2 MOA is required to win. So after settling on a load for this bullet, the next step will be to try that load with different 180 gr. GC bullet designs. If that doesn't produce 1/2 MOA, then I'll try a 3/4 or 1/2 degree throat. My gut feeling is that the short 1 degree throat is not optimal.

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Re: CBA loads

Postby mtngun » Sat Apr 01, 2017 8:08 pm

Continuing to walk up velocities with IMR8208. Groups #1-#3 were already shown in the previous post, groups #4 & #5 are what's new. As you can see, the velocity variation decreased as more powder was dumped into the case, but accuracy seemed to peak around 2300 fps. Above 2300 fps, it started throwing wild shots.
Image

Walking up velocities with Leverevolution. Groups #1-#3 were already shown in the previous post, #4 & #5 are what's new. All these groups used Rem 7 1/2 primers, and I'm not sure if that is the optimal primer for this ball powder? Nonetheless velocity variation tightened up nicely above 2300 fps.

Group #4 was the first group of the afternoon, from a cold clean barrel without a warm-up shot. The first shot was the low flier, and in my mind I cut it some slack since it was the fouling shot. Perhaps I should shoot a warm-up shot but I'm curious to learn whether the 1st shots go into the group -- sometimes they do, sometimes they don't.

Leverevolution seems to like 2300 fps.
Image

Well I need to choose one powder and one load so I can move forward, and all three of the semi-finalist powders seem to be about equal with a charge they like. I'm going to choose 34.8 gr. Leverevolution. If time allows I may tweak the charge just a little and try different primers, but 2300 fps seems to be where it wants to shoot. 2300 fps happens to be 118,000 RPM, which seems to be the favorite RPM for CBA competition.

The next major step will be to try different 180 grain bullet designs, but honestly there are only so many ways you can make a bore-riding spitzer. :lol:

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Re: CBA loads

Postby mtngun » Sun Apr 16, 2017 4:23 pm

Testing seating depth and one different primer. All of these loads used the 182 gr. Loverider, ~35BHN, BAC lube, and 34.8 gr. Leverevolution. Previously the bullet has always been seated to the jam point which is 2.540". However, there is no cut and dry jam point with a bore riding bullet -- the harder you push the bullet into the throat, the further it goes.

At any any rate, none of today's experimental seating depths shot any better than the 2.540" I had been using previously.

Then I tried a magnum primer. It was "OK" but no better than the Remington 7 1/2 that I usually shoot.

Basically these results confirm that my "best guess" load using the #7 1/2 and seating at the jam point was a pretty good guess.
Image

All in all, this bullet and load shows some potential but can't quite get its act together. Let's try a couple of different bullet designs.

The "Extreme Loverider" is the loverider concept taken about as far as it can go -- itsy bitsy bands that are widely spaced.

The "half and half" design has a traditional solid bore riding nose like your grandpappy used to shoot, while the bottom half of the bullet is a loverider. Bullets are shown after nose sizing in a 1 degree x 0.3005" die.
Image

I used the standard load of 34.8 gr. Leverevolution and seated to the jam point.

Aaand ... the Extreme Loverider was a step in the wrong direction.

The "half and half" was also a step in the wrong direction, compared to my usual loverider design. Some of the rounds were difficult to chamber -- it's harder to engrave a solid nose than a loverider nose -- and that shows up in the high ES.

These results confirm that my "best guess" loverider design was a good guess.
Image

Well, today's tests were a bit disappointing in the sense that no great groups were shot and none of the experimental loads were better than my old load. While there are always more powders and bullets to try, I feel that I've given this barrel a fair chance to show what it can do -- and the best it can do is 1 MOA with its pet load. One MOA is nice, but it won't win matches. I think the next step is to recut the throat.

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Re: CBA loads

Postby mtngun » Mon Apr 17, 2017 2:04 pm

The throat was recut to 1/2 degree per side. The same throating reamer was used to cut a matching nose die.
Image

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Re: CBA loads

Postby mtngun » Thu Apr 20, 2017 8:47 am

The wind was blowing 25 mph from 4:30 but the forecast called for things to get worse, not better, so I went ahead a gave the new 1/2 degree throat a whirl. I did not attempt to compensate for the wind, just held on the bullseye and let 'er rip. No doubt some of the diagonal dispersion was due to the wind but that's OK, I just wanted to get a feel for the new throat.

First up, the 180 gr. "XLR" bullet that I tested last time. As it happened the XLR bullet fit the new throat perfectly as it dropped from the mold, without needing to nose-size. I suspected that the XLR would shoot better in the new throat because of the fatter diameter, and indeed it did shoot better, though still not great. 1.47" average with the 1/2 degree throat vs. 1.68" last time. Admittedly not enough groups were fired to settle the matter but to my eye the groups simply looked better with the 1/2 degree throat and that was despite the 25 mph wind.

I also tried the XLR with a CCI 400 primer instead of the usual Remington 7 1/2. The CCI 400 boosted velocity by 30 fps, so it must be a hotter primer, but accuracy was no better and velocity variation remained poor.

Then I tried the XLR bullet with a final size diameter of 309 rather than the usual 3084. The actual diameter was not 309 because the as-cast diameter was only 0.3086" - 0.3088". Nonetheless, the velocity variation tightened up quite a bit with the 309 diameter. It may be that the XLR benefs from more engraving resistance, or it may be that the new throat is a little sloppier than the old throat and needs a fatter bullet.

In conclusion, the 1/2 degree throat did not harm the XLR bullet and may have helped a little. While the XLR is a failure as a competition bullet, it was a useful experiment to see how much full diameter bearing area a bullet requires to be accurate. There seems to be a trade off between full diameter bearing area vs. distortion -- more full diameter area improves support but increases distortion when the bullet is engraved. The XLR minimized distortion but didn't have quite enough full diameter support. Even so it still averaged 1.47" at 2300 fps in a 25 mph wind.
Image

Now on to the 182 gr. GC Loverider, which averaged 1 MOA in the 1 degree throat. Unfortunately, its as-cast diameter was too small to be a good fit in the 1/2 degree throat. Also it was jamming on band #5 (counting from the bottom) instead of on the front band as I prefer. Aaaand to be a jam fit it had to be seated out so that only the GC was inside the case. In fact, one of the loaded bullets fell out of the case when I picked it up -- not good. I normally aim for 0.120" - 0.140" to be inside the case when the bullet is seated for a jam fit. By trial and error I have found that is the minimum to grip the bullet securely even by benchrest standards.

The first 5 shots were looking good. Shot #6 was the one where the bullet fell out of the case. I simply put it back in the case with finger pressure and shot it that way -- it was a low flier. :evil: Then 3 more fliers made for the worst group this bullet has ever shot. :evil:

The 1/2 degree throat definitely hurt the 182 gr. Loverider, but in fairness, there were issues with the bullet fit and the seating depth. I will recut the mold and hopefully get the bullet fit straightened out, and give it another whirl.

This lousy group illustrates the problem with long throats and long leades -- they need a long, fat bullet to fill them up. :lol: People talk about sizing the bullet to fit the throat but the reverse is also true -- the throat needs to be selected to fit the bullet.
Image

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Re: CBA loads

Postby mtngun » Sat Apr 22, 2017 9:17 am

Last time the 182 gr. Loverider shot poorly in the 1/2 degree throat, but it was too small to fit the throat properly. So I recut the mold to make the bullet fit the throat perfectly. As you can tell by the bullet dimensions, the throat is pretty long, longer than I had intended. It has a good 0.200" of freebore whereas I actually wanted little or no freebore. The top band is 0.3034" whereas I actually wanted it to engrave the throat at 0.3015". In theory it is possible to recut a throat to a gentler angle without making it longer, but in practice it usually ends up longer, and that's what happened here.
Image

The target speaks for itself -- the Loverider still shot lousy, only not quite as lousy as last time. It simply does not like this throat. :cry:

The Loverider had preferred 0.3084" diameter in the original 1 degree throat, but since this 1/2 degree throat is sloppier I tried both 0.3090" and 0.3084" (due to springback the actual diameters run a little bigger). As you can see it seemed to prefer 0.3090" though neither target was satisfactory.
Image

Off-topic but interesting -- this batch of bullets had very loose gas checks, to the point that about 1 out of 10 checks came off while lubing & sizing. Yet none of today's rounds lost their checks. I have never seen a correlation between check fit and checks coming off in flight.

Obviously the 1/2 degree throat experiment is a failure with the Loverider, :oops: though it did improve accuracy slightly with the Extreme Loverider. Some CBA competitors like Tom Grey have successfully used 1/2 degree throats (though with 200 grain bullets) so I'm not condemning all 1/2 degree throats, it's just that my particular bullet does not like it. Also, there is the freebore issue.

The throat definitely makes a big difference, for better or for worse. The search for the perfect cast bullet throat continues.

Before I give up on the 1/2 degree throat, I would like to try a 190 gr. bullet. The 1 degree throat did not like the heavier bullets but this throat has different taste and in theory the longer throat should favor longer bullets.

If a 190 gr. bullet also shoots patterns, then I'll set the barrel back and rechamber. The question is, what should the next throat be like? The jury is still out on throats, but here are some observations:

-- the 1 degree throat was 1 MOA with its pet load, so that's not bad.
-- I've had good results with 1 degree throats in some other barrels.
-- I've rarely had good results with sloppy throats, at least not at higher velocities (my 357 Contender was an exception and it was only 2000 fps). Best results seem to be with a throat entrance that is 0.0005" - 0.0010" larger than the groove diameter.
-- I haven't had good results with long freebore. Best results have been with either zero freebore or a short (0.050" freebore).

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Re: CBA loads

Postby mtngun » Wed Apr 26, 2017 4:59 pm

A new 190 gr. Loverider to test in the looooong 1/2 degree throat. The nose fit the throat perfect as it dropped out of the mold so there was no need to nose-size. It was final-sized in a 0.309" die but due to spring back actually ended up 0.3094" - 0.3096". The ready-to-shoot weight was about 192 grains.

It's Miller Stability factor in this 14" twist barrel is 1.3 at sea level, or 1.54 at my elevation. It's my understanding that SF=1.3 is about as low as you want to go for benchrest shooting.
Image

For some reason velocities have been running high since I recut the throat to 1/2 degree. For the 2nd group I tried reducing the powder charge to 34.4 gr. of Leverevolution, which dropped the velocity down to the sweet spot of 2300 fps.

As you can see, both groups had one wild flier. Even if I knew how to get rid of the flier, the remaining 9 shots would not win any matches. This kind of accuracy might be fine for hunting or plinking, but it's useless for competition. :x
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One shot from the 34.8 gr. load threw a gas check. The checks are a perfect fit on this particular bullet. I have no theory as to why this particular bullet & load threw a check. :?
Image

OK, so I've given the loooong 1/2 degree throat a fair chance and it could not even do 1 MOA. I suspect the fault lies in the execution of the rethroating job -- running the reamer in deeper than I had intended -- not in the angle per se.

Time to set the barrel back and try plan "C". Perhaps a 3/4 degree throat this time? The only thing I'm sure of is that it will be either zero freebore or at most 0.050" freebore, with a 0.3085" - 0.3090" entrance.

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Re: CBA loads

Postby mtngun » Fri Apr 28, 2017 12:42 pm

Update: an "autopsy" of the 1/2 degree throat, conducted by measuring how far various gage pins would enter the throat, showed that the entrance to the throat was 0.312" and a 0.3089" pin could be inserted 0.253" into the throat. So the 1/2 degree throat was definitely waaaay too sloppy as well as way too long, and the 0.309" bullets I was shooting were too skinny for the sloppy throat. That was my fault for being overconfident in setting the reamer depth. :oops: I should have cut a little bit at a time and paused to measure in between cuts.

In my defense, it's difficult to measure the progress when recutting an existing throat. When I'm cutting an original throat I use a groove diameter gage pin to judge the throat depth -- i.e., cut just deep enough to allow a groove diameter pin to barely enter the throat. That method doesn't work when recutting an existing throat, so guesswork is involved, and in hindsight I guessed wrong. :cry:

Also, the original chamber neck had always been a little too long, with about 0.040" gap between the end of the case neck and the beginnning of the throat. I'll try to close that gap on the next chamber.

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Re: CBA loads

Postby mtngun » Sat Apr 29, 2017 7:24 pm

I set back the barrel and recut the chamber & throat. The shortened barrel is about 26 1/2" long. The chamber neck is still the same 0.330" - 0.331" diameter.

I took care to minimize the gap between the case neck and the entrance to the throat. The original chamber had a gap about 0.040" long, now it is only 0.010" - 0.020" (it's difficult to measure precisely because there are several variables).

I decided to use the same 1/2 degree throat reamer as last time, but with minimal freebore and minimal clearance. Last time the throat ended up with over 0.250" freebore, this time there is 0.050" freebore, if even that. Last time the entrance to the throat was 0.312", this time it is 0.3090", if even that.

For the time being I assumed that best accuracy would be with the bullets nose-sized to jam with only one band seated into the case. That is a system that has worked well for me in my high-velocity barrels though admittedly I have not done comparison testing in this mid-velocity application.

Here is how the bullets looked after nose sizing. As you can see, they look nearly the same as the bullets for the original one degree throat -- 1/3 to 1/2 of the bullet ends up being a bore rider. :? I'm not convinced that bore riding section is a good thing, but we'll give it a try.
Image

Bullets were seated at a hard jam point. There was some mid-day mirage and a 5 - 15 mph wind that was constantly changing speed and direction, but the forecast called for conditions to get worse, not better, and I was eager to try the snug 1/2 degree throat.

From left to right, starting with the 180 gr. Loverider. I was aiming for 2300 fps but velocities were a little high. Nonetheless 9 shots went into 0.9". The one flier happened when the wind completely reversed directions and I thought "well I'll just hold steady on the bullesye and see what happens." Well, the flier happened! :lol: On the next shot I held windage and it went into the main group, so the flier may have been my fault for failing to dope the wind.

Next, I dropped the powder charge 0.3 grain down to 34.1, yet the velocity was still too high. 9 shots went into 0.8".

Then I tried the XLR bullet. This throat did not like the XLR, probably for the same reason the original 1 degree throat did not like the XLR -- not enough support.

Then I tried the 190 gr. Loverider. This throat did not like the 190. No surprise because the original 1 degree throat did not like a 189. I sure wish I could find a 190 that would shoot in this barrel because CBA competitors prefer heavy bullets for less wind drift.

I had only five 180's left so I shot them with 33.8 gr.. The 2297 velocity was what I wanted. 4 shots in less than an inch but one flier. I can't rule out wind for the flier because it kept changing direction and speed.
Image

Conclusions
-- this snug 1/2 degree throat behaves similar to the original snug 1 degree throat.
-- I still have to size noses more than I would prefer, with about 1/3 of the bullet ending up as bore rider.
-- while the jury is still out on the perfect cast bullet throat, I feel good about the gunsmithing on this chamber and throat. The dimensions turned out just the way I wanted. :)
-- at the moment I'm inclined to believe there isn't much practical difference between a 1/2, 3/4, or 1 degree throat. What matters is a snug fit.
-- this throat shows potential with the 180 Loverider, if I can get rid of the one flier in every group.
-- in case you are wondering, I'm deliberately sticking with 180 - 190 gr. bullets at 2200 - 2300 fps because those are weights and velocities that CBA competitors are comfortable with. I would not be the least bit surprised if this barrel gave better accuracy with a lighter bullet, and I may try that eventually, but for now I'm sticking with conventional CBA loads just because that's what people expect.

Things To Try Next Time
-- try nose-sizing just enough to make the top band 0.3015", even though it will require deeper seating.
-- 33.9 gr. Leverevolution seems to be the recipe for 2300 fps.
-- as time allows, keep trying different 180 - 190 gr. bullet designs.
-- these experiments with cutting different throats have convinced me that it would be handy to have micrometer depth stops for the reamers. It may be a while before I can build them, but they've been added to my wish list.

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Re: CBA loads

Postby mtngun » Wed May 03, 2017 9:41 am

FYI: the Flickr photo host that I have been using lately sometimes gets overloaded and then the photos don't show. So if you can't see photos, that's probably why. Just try again another day and eventually it starts working again. :(

Today we tested a different nose-sizing & seating strategy. Instead of sizing the nose so that the bullet could be seated with only one band inside the case, as I have been doing previously, I sized the nose just deep enough to make the top band 0.301". That resulted in much deeper seating. The idea was to replace the bore-riding nose with a tapered nose that would provide more support for the bullet once it got underway.

First up the 180 gr. Xtreme Loverider (XLR) that shot a 3" pattern last time. Today it shot the best group, 1.00". It definitely benefited from today's sizing/seating strategy. :) No surprise since the XLR needs all the support it can get.
Image

Next the 180 gr. Loverider.
Image

Next the 190 gr. Loverider. It may have benefited from today's sizing/seating strategy, though it's still not accurate enough for competition purposes.
Image

These semi-spitzer Loverins were leftover from a 30-06 project. They were in an unlabeled box and, in hindsight, half the bullets in the box were 190's and half were 200's. Due to the pudgy design and dense COWW alloy they are short relative to their weight, and should stabilize in the 14" twist. But I didn't notice the two different weights until I went to shoot them, so I ended up shooting 4 190's and 6 200's into the same group. Neither acted like it wanted to group, but at least they stabilized, confirming Miller's stability rule.
Image

From left to right:
#1 XLR
#2 180 Loverider. Not really any better than last time.
#3 190 Loverider. An improvement over last time.
#4 190 & 200 gr. semi-spitzer Loverins. 4 shots were 190 gr. and 6 shots were 200 gr., and the 200's impacted a little lower.
Image

After all the shooting was done, I noticed that one gas check had come off and dinged the muffler exit. I don't know which bullet was the culprit.
Image

Conclusions
-- today's sizing/seating strategy definitely benefited the XLR, and may have benefited the 190 gr. Loverider.
-- it's not clear that today's sizing/seating strategy benefited the 180 gr. Loverider.
-- velocity variation was generally good today with all bullets. The fatter nose increases engraving resistance, which makes the powder burn better, and the deeper seating improves the load density.

Things to Try Next Time
-- maybe an in-between sizing/seating setting for the 180 gr. Loverider?
-- retest the XLR to see if its 1.00" group is repeatable?
-- maybe a Loverider design that is halfway in between the XLR and the standard Loverider?
-- maybe an XLR 190 gr.?
-- since the XLR designs seems to be telling us that it likes more support, perhaps another way to give it more support is with a harder alloy? But I'll hold off on that until I am ready to do an alloy shootout in this barrel.


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