CBA loads

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Re: CBA loads

Postby mtngun » Wed Jun 21, 2017 12:43 pm

A 1/4" drive torque wrench showed up, so now I can torque the action screws. I don't expect the torque wrench to make any practical difference but nonetheless it offers peace of mind, especially since this switch barrel action is frequently removed from the stock in order to swap barrels or to clean the Jewell trigger.

OK, so what is the optimal torque for the action screws?
-- Remington specifies 30 - 35 in-lb for wood stocks or 45 for synthetic.
-- internet buzz suggests you can go 40 - 60 in-lb if the action is pillar bedded.
-- the max torque recommended for a 1/4-28 grade 5 screw is 87 in-lb (my screws are prolly grade 8 but I'm derating them because thread engagement in the action can be less than ideal).
-- even though my action is pillar bedded in the birch laminate stock, ultimately the force must be transferred to the birch stock which is pretty soft, so I am worried about damaging the stock if I overtighten the action screws.

For starters I tried 35 in-lb. I'm guessing that is less tight than I had it before when I tightened them by hand.

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Re: CBA loads

Postby mtngun » Wed Jun 21, 2017 2:16 pm

Behind the bench at 5:30 a.m. before going to work. No wind and no mirage! 8-)

Once again the barrel was cleaned with a brass brush and Ed's Red between each group. 11 shots including a fouler were fired at each target. If the fouler had landed within the group I would have counted it, but as it happened all of today's foulers were about 3/4" high at 12 o'clock. Sometimes one fouling shot seemed to be adequate, while other times the POI seemed to walk for 2 or 3 shots before it settled down.

Last time the experimental RL15 load was slower than intended so I wanted to try RL15 again at 2300 fps. The idea is to test all loads at 2300 fps so it's an apples to apples comparison, however, once again I mis-guessed the powder charge and this time the load was faster than intended :evil: Oh well, it's still useful data.

The 32.2 gr. 8208 load was a repeat of last time except with the ALR (agressive loverider) instead of the PLR (plain loverider). One flier spoiled what would have been an MOA group.

The 34.8 gr. 8208 load was just for giggles, to see how it would react to more velocity. It did not like 2500 fps, which is puzzling compared to, say, the accuracy of my 14" twist 7BR that averages 1 1/4" at 3000 fps.
Image

A summary of the borecam results, all taken at the same spot about 8" from the breech. As usual the borecam quality leaves a lot to be desired (it's next to impossible to keep the optics clean and even the tiniest spec of dust or smudge gets magnified on the photo, plus I need to learn how to adjust the brightness :lol: ) but nonetheless you can discern differences in barrel condition. My take is that today's RL15 load was perhaps cleaner than last time (because the higher pressure helped it burn cleaner) and there's not much difference in carbon fouling between today's RL15 load vs. today's 8208 loads. Unfortunately today's RL15 loads, despite being cleaner, were not as accurate as the slower RL15 loads shot last time. That being the case, I've decided to make 32.2 gr. IMR8208 my new standard load.
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I experimented with cleaning with a plastic brush rather than a brass brush. The plastic brush left lots of dark streaks.
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Then I JB'd it with a tight fitting patch. That got rid of most of the dark streaks, but even so it's not perfectly clean like a new barrel.
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I haven't settled on a cleaning routine yet. How clean does the barrel need to be for optimal accuracy? How many shots can be fired with IMR 8208 before accuracy deteriorates? This carbon fouling business is new territory for me and I don't have it all figured out yet.

The good news is that I've settled on 32.2 gr. 8208 as my new standard load. The bad news is that today's groups were nothing to brag about, and even on a good day this barrel struggles to break the 1 MOA barrier. I beginning to wonder if it is doomed to be a mediocre barrel, but there's still things I want to try before I give up on it.

Things To Try Next Time:
-- settle on the PLR as my standard "control" bullet? I'm not even sure that I still have that cavity, it may have been the one I recut to a solid nose.
-- I'm debating whether to fire a few more firelapping shots (the barrel has 10 firelap shots to date). The barrel looks smooth enough to my eye and it's possible the Leverevolution carbon fouling would have happened in any barrel.
-- I would like to find a quick and easy cleaning method that leaves the barrel as clean as when it was new.
-- determine how many shots can be fired with IMR8208 before accuracy deteriorates.
-- perhaps try increasing the front action screw torque to 50 in-lb.
-- redo some of my earlier experiments, like the solid nose experiment, because I now realize those experiments may have been compromised by the carbon fouling problem. :|

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Re: CBA loads

Postby mtngun » Wed Jun 21, 2017 2:51 pm

I went back and looked at the borecam images of various barrels that I took when my Lyman borecam was new. They are 10X better quality than the current images. For example, this pic of an Xcaliber barrel:
Image

I just gave the Lyman mirror a good cleaning and examined the mirror under magnification -- it appears clean enough but nonetheless has a hazy area that is not affected by cleaning. I'm guessing the mirror is actually damaged somehow. Bummer because I really liked the borecam when it was new. :cry:

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Re: CBA loads

Postby mtngun » Fri Jun 23, 2017 5:34 pm

An import wind meter showed up. To my surprise it actually seems to work well.

At the moment I don't have any "real" wind flags, just pieces of surveyor's tape tied to the 50 yard target posts. With the tape flying at approximately 45 degrees from vertical, the meter reads 4.9 mph.
Image

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Re: CBA loads

Postby mtngun » Sat Jun 24, 2017 6:53 am

Behind the bench at 5 a.m.. No wind or mirage. 8-)

Since last time, I increased the torque on the front action screw to 45 in-lb. The rear action screw was left at 35 in-lb. I don't expect the torque settings to make much difference just as long as the screws are not loose, but nonetheless I'd like to settle on the 45/35 setting as my standard, just for consistency and peace of mind.

Since last time I scrubbed the barrel with Seafoam and a brass brush. The Seafoam did seem to remove some carbon that the previous cleaning with Ed's Red and JB had left. Here's a pic after cleaning taken with the Russian borescope and a point & shoot camera approximately mid-barrel. The dark lines perpendicular to the bore appear to be some sort of optical refraction within the borescope that were enhanced by this particular photo, normally you don't see the perpendicular lines when looking through the scope with the naked eye. Anyway, the point is that the barrel looked clean at the start of the test.
Image

I haven't had time to prep any new bullets so in the meantime I'm shooting a variety of bullets left over from previous tests, in case you are wondering. Also I am trying to collect BC data for a variety of bullet weights and designs.

The barrel was cleaned in between groups with a brass brush and SeaFoam. I tried using SeaFoam with a plastic brush, but it left dark streaks so I gave up on the plastic brush. SeaFoam seems to remove carbon at least as well as Ed's Red, but a brass brush still seems to be essential.

A fouling shot was fired at the target, and it so happened that all of today's fouling shots landed within the main group.

The 124 grainer was designed for 18" twist barrels, but I wanted to shoot it today in the Shilen just to collect BC data. However the Shooting Chrony would not read in the early morning light, so I'll have to retest the 124 later in different light conditions. I had not expected the 124 to shoot well in the 1/2 degree throat with the random powder charge, but it did. :) I tried to take a borescope photo after shooting the 124, but the photo didn't turn out so you'll have to take my word that there was only very light fouling.

The 193 grainer had been tested with 8208 before on a windy day, so this was a retest under good range conditions. It acted like it wanted to shoot if not for the 2 vertical fliers. The velocity variation was good and the shots felt good so I don't know what caused the vertical. :?: The borescope showed moderate carbon fouling mid-barrel after shooting the 193's with IMR8208 (but the photo did not turn out). When pushing the brush through a fouled barrel, I could definitely feel a tight spot in the middle of the barrel. I believe the tight spot is due to carbon. After several strokes the tight spot went away.

6 shots of the 182 CLR (because I only had 6 bullets left) produced a shotgun pattern. I have no explanation for its sorry performance. Again there was moderate carbon fouling mid-barrel, and again I could feel a tight spot at mid-barrel when pushing the brush through the fouled barrel.
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The 124 gr. bullet lost one gas check, but the shot still landed in the group.
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Observations, and Things To Try Next Time:
-- the decent performance with the 124 and the 193 make me feel OK about torquing the action screws 45/35.
-- retest the 124 for BC.
-- is the carbon fouling in the middle of the barrel unavoidable due to normal combustion products, or is it caused by some invisible flaw with the barrel itself? It seems strange that this barrel has a carbon fouling problem that I've never noticed with any other barrel.
-- I may push a soft slug through the (clean) barrel to check for tight spots.
-- I'm leaning toward trying more firelapping shots.
-- I could keep trying more bullet designs, but I'm not convinced that bullet design is the big hangup at this point. Even after switching to a cleaner powder and cleaning after every group, the barrel still seems to develop a tight-spot due to carbon fouling. It stands to reason that the tight spot will hurt accuracy with cast bullets. I think my focus needs to be figuring out that tight spot.
-- first impressions of Seafoam are good -- it cleans carbon at least as well as Ed's Red, and all of today's fouling shots landed within their group.

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Re: CBA loads

Postby mtngun » Sat Jun 24, 2017 7:23 pm

Trying again to test the 124 gr. Loverider BC, this time in the late afternoon. 3 mph breeze, occasional 1/8" jiggle mirage.

The useful sensor area on the Shooting Chrony is pretty small, as shown by the dotted line on the photo. You better have confidence in your load if you want to try this at 100 yards. :lol:
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Of course the barrel was cleaned prior to shooting. As I mentioned in a previous post, the horizontal lines are merely some sort of optical diffraction in the borescope and they get enhanced by some of the photos. Normally you don't notice them when you are looking in the bore scope with your naked eye.
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After shooting 11 rounds with the 24.0 gr. RL10 load at 2043 fps. Only light carbon fouling, and I did not feel a tight spot when I pushed the brush through the barrel.
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After shooting 11 rounds with the 34.0 gr. RL10 load at 2888 fps. Sorry for the photo being slightly out of focus. :( Moderate gray-colored carbon fouling, but still I did not feel a tight spot when I pushed the brush through the barrel.
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Both fouling shots landed at 12 o'clock relative to the rest of the group but nonetheless they were within the group. The hi-velocity load threw the 2nd shot out of the group, but then settled down and threw the remaining 9 shots into one ragged hole. Neither load would win matches but nonetheless they did better than I expected considering they were not designed for this 1/2 degree throat and the powder charges were arbitrarily selected. Maybe the lack of severe carbon fouling helped?
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The BC results. I'm seeing a trend with my spitzer bullets that the G1 BC is approximately the same as the bullet's sectional density (for this bullet the SD = 0.190). That makes sense because the ogive is similar to a G1 ogive, and for a G1 form the BC=SD.
Image

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Re: CBA loads

Postby mtngun » Mon Jun 26, 2017 5:02 am

Behind the bench at 5 a.m., but we're having a heatwave and even at 5 a.m. there was 1/8" mirage jiggle.

I'm still debating what to do about the carbon fouling problem. The change to IMR8208 and cleaning in between groups definitely has helped, but even with the cleaner burning 8208 there is still significant carbon fouling and I'm wondering if it is enough to cause the occasional flier? While I'm contemplating the problem I may continue to experiment with alternative powders.

RL10 seemed to burn cleanly with the 124 gr. bullet so I thought I would try it with a heavy bullet. I'd tried RL10 early on and it didn't do anything noteworthy -- it struck me as being faster than ideal for heavy bullets, which prefer a gentle push.

Well, the borescope says that RL10 is definitely a cleaner than average powder. It merely leaves a light grey haze in the barrel, no black or brown streaks. :)
Image

The bad news is that I mis-guessed the powder charge and the velocity was faster than my 2300 fps goal. The poor accuracy may be in part due to the 2384 fps velocity, but nonetheless it reinforces my opinion that RL10 slaps the heavy bullets a little too hard.
Image

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Re: CBA loads

Postby mtngun » Tue Jun 27, 2017 1:55 pm

Today another BC test and a couple of powder tests.

This was a bullet made for my 18" twist 30BRs. Since then I have stopped coating GC bullets because, while the coating doesn't hurt anything, it doesn't necessarily help, either. Also since then I have for the most part switched to Loverider designs because they seem a little more forgiving under certain circumstances, with no downside that I am aware of.

If and when I have time to play with my 18" twist barrels again, I would like to try a 125 - 130 gr. Loverider with a cone ogive. In theory a cone ogive should improve the pathetic ballistic coefficient of these stubby bullets and I can't think of any reason it would be less accurate, if all other things are equal.
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All of the loads in this shooting session had lousy accuracy and I don't know why since the velocity variations were decent and none of the powders were particularly dirty. Normally I would have included a control load as a comparison, but I have yet to make a batch of bullets for the control load.

"PLR" refers to the "Plain Jane" 183 gr. Loverider.
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In between groups the barrel was cleaned with a brass brush & either SeaFoam or Hoppe's #9. Here's a side by side comparison of the bore after shooting each load, as viewed through my Russian borescope 12" from the muzzle. Note that back when I was using a Lyman Borecam the most carbon-fouled spot was 8 inches from the breech, but the Russian borescope cannot reach that spot while the barreled action is in the stock. Point being that even if the bore is clean 12" from the muzzle, it might not be clean 8" from the breach.

As usual RL10 was exceptionally clean, leaving only a light grey haze.

Benchmark was mostly clean but did have some darkness in the corners of the grooves.

With Varget you start seeing some black streaking, though it's still relatively clean compared to the totally sooted bore created by Leverevolution.
Image

Hard vs. Soft Carbon Fouling
In a previous post I mentioned claims that some powders leave soft fouling while other powders leave hard fouling. That may be true but I have no way to measure the BHN of carbon fouling! :lol: However, if the fouling is soft, then wouldn't the next bullet scrape most of it out? If the fouling is soft, then wouldn't it clean up with just a patch and solvent, or perhaps with a plastic brush and solvent? Since none of the dark fouling that I have observed thus far has cleaned up with merely a patch or merely a plastic brush, I am going to assume that all dark streaks are "hard" carbon fouling that are capable of damaging a cast bullet.

Where Do I Go From Here?
This barrel was intended to be a vehicle to test experimental bullet designs and to test the concept of a 14" twist for target shooting, but instead I spend most of my time trying to figure out why the barrel's accuracy is at best spotty and why the barrel has a carbon fouling problem that I've never noticed with my other barrels. I've made some progress by switching to a cleaner powder and by cleaning in between groups, but accuracy still seems fussy.

It is a fact that some barrel just don't shoot as well as others. It would be nice to be able to test the same loads in a 2nd barrel as a sanity check. I.e. if a particular load causes both barrels to have carbon fouling and poor accuracy, then I would know the load is to blame, not the barrel. But if a particular load shot cleanly and accurately in one barrel but not the other, then I would start to suspect something is wrong with the uncooperative barrel.

Rather than buy yet another barrel that I can't afford, I'm thinking to press one of my 18" twist Kriegers into service. I'd have to use a bullet that is compatible with both the 18" twist and the 14" twist, but in theory that can be done. Ideally both chambers would be cut with the same reamers so they could digest the same ammunition. So that is my tentative plan. It's going to take some time to set up because I'll need to chamber the Krieger and cut a mold for the special bullet.

In the meantime I may continue to poke around with more BC tests and more powder fouling tests, but I don't see any point in attempting bullet design shootouts until I have confidence that the barrel is capable of consistent accuracy.

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Re: CBA loads

Postby mtngun » Thu Jun 29, 2017 7:42 pm

A couple more powder cleanliness comparisons. The barrel had been brushed after the last session, but just to be sure it was clean I JB'd it before shooting today. The JB patch kept coming out black, and I could feel roughness in the usual spot about 8" from the breech. The roughness went away after pushing the JB patch through several times. In other words, I suspect there was carbon in that spot that had not been removed by brushing.

H4895 was cleaner than average.

H335 was starting to show some dark streaks, plus there appears to be lead in the corner of the groove.

Brush and solvent suffice to get this section of the bore clean, but the Russian borescope can't reach the problem spot" 8" from the breech without removing the barrel from the action.
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UPDATE: I unscrewed the barrel so I could examine the breech end with the Russian borescope. The usual "bad spot" 8" from the breech looked good -- no carbon, no lead, and no visible pitting. But I could see a tiny bit of lead in the corners of the grooves, starting at the throat and continuing for several inches. The lead doesn't show up well in the photo so you'll have to take my word that I can see more detail with my eye than through the camera. Yes, I am picking nits -- normally I am a slacker when it comes to barrel cleanliness as long as the barrel shoots satisfactorily, but in this case the barrel is not shooting satisfactorily so I am trying to understand why.
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I screwed up the powder charge for H4895 such that it was 2417 fps instead of the intended 2300 fps. H4895 had shot MOA on March 19 but that was at leisurely 2239 fps. According to Quickload, the 2417 fps load generated 51 ksi while the 2239 fps load generated 41 ksi. In general, H4895 seems to be a good powder for cast bullets as long as you don't push it too hard.

Because I was running out of bullets, I had to use two different batches of ALR bullets for the WC844 target. The two batches had slightly different seating depths, which you wouldn't think would make a difference, but as it turned out one batch impacted lower than the other batch.

I was disappointed with these groups, even allowing for the powder charges not being optimized and using mixed batches of bullets. This barrel strikes me as being awfully fussy with cast bullets.
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One gas check parted company with its bullet but I didn't notice it until I had finished shooting, so I don't know which shot was responsible or whether it landed within the main group.
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Thoughts:
-- some powders are definitely cleaner than others, but cleanliness doesn't correlate to accuracy as long as you clean the barrel after every group.
-- I keep thinking this barrel is very fussy with cast bullets. Yes, it can shoot 1 MOA with its pet loads and a squeaky clean barrel, but accuracy drops off a cliff with powders it doesn't like, with too much velocity, too much pressure, or with a dirty barrel.
-- Previously I had talked about setting up a comparison test with a Krieger 18" twist barrel, and I may still do that, but I don't need a comparison test to tell me that this Shilen is a fussy barrel.
-- I would not rule out the possibility that the barrel has become "shot out." I don't keep a tally of shots fired but would guess it's up to 1000 - 1500. The mild mannered 30 BR has a reputation for letting barrels last 2000 - 3000 rounds, but every barrel is different. Update: a borescope inspection of the the breech end showed no visible erosion.
-- I'm kicking several options around but I want to think about it for a while, and perhaps remove the barrel from the action so I can borescope that "problem spot" 8" from the breach.
-- my latest theory is that I am "slapping" the bullets harder than they care to be slapped. My goal of a 180 - 190 gr. bullet at 2300 fps requires 40 - 45 ksi in the BR case. By comparison, most CBA competitors are launching 190 - 200 gr. at 2100 - 2200 fps with VV135, which requires only 35 - 40 ksi. It may be that I either need to 1) reduce my velocity to 2100 - 2200 to keep the pressure below 40 ksi or 2) use a slower powder or 3) use a larger case like the 308 Winchester.
-- I have no interest in the slow heavy bullet approach -- yes, it works, but it's already been done a million times before.
-- So I'll try a slower powder or two, and contemplate rechambering to 308 Win. The 308 could hit my goal of 2300 fps with only 35 - 38 ksi, assuming you could find a powder that burns well at that pressure.

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Re: CBA loads

Postby mtngun » Fri Jun 30, 2017 4:20 pm

More on the "slapping too hard" theory ....

It took me a while to find it, but Quickload does indeed calculate the acceleration of the bullet. Here's how to find the acceleration chart after you have satisfactorily entered your load data: 1) regardless which type of chart you have displayed in Quickload, click on that chart's "maximize" button. 2) now you should see a "Change Diagram" menu. Click on it. 3) click on "Optional Diagrams." 4) select "Acceleration." Place your cursor at the peak of the acceleration curve and it should display the result in G's. Example below.
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Here's some acceleration numbers for a few loads. For comparison, I included the loads of 2016 CBA competitors whose gas check bullets averaged 1.10" or less for ten-shots at 100 yards -- they must be doing something right! 8-) 8-) 8-)
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What stands out is that my load's pressure and my acceleration are higher than average. In theory, rechambering to 308 Winchester would drop my pressure and acceleration down to typical CBA levels. Emphasis on "in theory" because it can be tough to find a rifle powder that will burn well in a big case at low pressure.

Let's sum up today's Unified Theory of Gas Checked Cast Bullets: to win in the CBA, a cast bullet load should operate at no more than 123,000 RPM, at no more than 36 Ksi, and at no more than 92 G's. The Miller Stability Factor should be no less than 1.3 (I say that based on conventional wisdom in the jacketed benchrest community), but admittedly some people are getting away with a slightly lower stability factor. I'm not going to put a cap on velocity because I don't see it as a limitation providing those other criteria are met.


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