CBA loads

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mtngun
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Re: CBA loads

Postby mtngun » Wed May 03, 2017 7:28 pm

Retesting the "Extreme Loverider" (XLR) load that shot 1.00" this morning. I wanted to see if the 1.00" group was repeatable, or just luck. One bad group is sufficient to prove that a load is bad, but one good group is not sufficient to prove that a load is good!
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Apparently some luck was involved with the 1.00" group because it couldn't break 1 MOA again, though a shifty 5 mph wind (0.6" drift at 100 yards) may have played a role. Nonetheless, the overall performance (1.24" average for the 3 groups) is still better than this oddball bullet had done with any other load/throat combo, so today's sizing/seating setting was definitely a step in the right direction.
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Note how the POI is lower on the right target? That has me wondering what caused the POI to fall? The target on the right was actually on a lower row than the target on the left, I merely cut and pasted them side by side in the photo editor to make the final picture less cluttered. I'm wondering if lowering the rest for the right target somehow affected the POI? Hmmm ....
Image

Conclusions
-- today's nose sizing/seating setting was definitely a step in the right direction, confirming my theory that the nose needed a little more support.
-- velocity variation was defintely better with today's nose sizing/seating setting.
-- I am increasingly aware of how important wind doping is for CBA-level accuracy. Wind doping is not critical if you are content with 1.5" accuracy. When shooting high velocity cast that struggles to hit 1 MOA, I usually don't even bother to hold for wind. But that does not work with these 2300 fps loads. Even with the heavy spitzer bullets, a 5 mph puff of wind moves the bullet 0.6" at 100 yards. If the wind reverses direction, as it did several times today, that's a possible 1.2" added to the group by a breeze that is so gentle you wouldn't be aware of it unless you had a wind flag !
-- next time try to keep all the groups for a given load on the same row of targets, and watch for POI/accuracy shifts when changing rows.
-- on the downside, I am still nowhere near match grade accuracy, and have yet to improve on the 1 MOA average of the original throat's pet load. :cry:

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Re: CBA loads

Postby mtngun » Tue May 09, 2017 7:40 pm

Today I tried a new bullet. Since the "Extreme" Loverider (XLR) seemed to be just a little shy of support, I split the difference between the Extreme Loverider and the Regular Loverider and called it the "Aggressive" Loverider (ALR), because it's more aggressive than a regular Loverider but not as aggressive as the Extreme Loverider. The only difference is the GtoB -- the ALR's GtoB is 1.3, halfway between the XLR's and the Regular's. You have to look closely to notice that the ALR's bands are just a little bit longer than the XLR's bands. The theory was that the longer bands should provide a little more support.
Image

Since the ALR is nearly the same as the XLR, and since the XLR shoots nearly the same (1.24" average) as the regular Loverider (~1.2" average), I expected the ALR to shoot about the same 1.2", too. But it had other ideas. :twisted:

There was outside mirage making the target jiggle 1/4", and a 0 - 10 mph wind that often changed speed and direction. I have not had much luck with range conditions lately.

I started with the same 34.8 gr. LVR load that I used last time with the XLR.

From left to right:
-- the first target on the left was a mediocre 1.20", about what I expected, especially considering the mirage.
-- second target, I tried RL15. Previous powder tests in the original throat had RL15 shooting just as well as Leverevolution. But a lot has changed since then, a different throat and a different seating depth. Well, today it did not like RL15 ! That seemed strange.
-- third target, back to Leverevolution but I dropped the charge to 34.4 gr. Nonetheless the velocity went up, not down. Velocity variation improved, yet vertical dispersion increased. That seemed strange. In mid-group, the bolt release stuck in the open position. It had given me problems sticking a while back and I thought I had fixed it by cutting more clearance inside the stock where the bolt release was rubbing. Something must have shifted? It's not good when bedding-related things shift. I checked the action screws -- tang and forward screw still tight, middle screw still just snug. However, I noticed that I could free the bolt release by backing the middle screw off one turn. Something must be flexing when the middle screw is snugged? So I cut more clearance for the bolt release and assembled the middle screw 1 1/2 shy of snug -- basically the middle screw is just sitting there, not putting any force on the action.
-- 4th target, a repeat of 34.4 gr. LVR with the sticky bolt release situation fixed. Less lousy, but still lousy. :x
Image

The ALR bullet was cut with a snug fitting check shank, whereas the XLR check shank tends to be a little loose. Nonetheless 3 out of 41 ALR bullets lost their checks today. 2 of the errant checks happened during the 1st 4 shots. The 3rd errant check happened with RL15. I have no explanation for the errant checks, other than to say that it does not correlate to check fit.
Image

Conclusions:
-- today was a Murphy's Law day when nothing seemed to go right. :cry:
-- there is no great love for the ALR bullet, but I don't know why, since it is very similar to the other Loverider bullets.
-- I may need to experiment with action screw tightness. Otherwise I don't know what I can do about the bedding. It already has pillar & Devcon bedding. However,the M700 action design doesn't have a lot of bedding area at the tang and hardly any bedding area in the middle, plus the M700 is a flexible action by benchrest standards.
-- the errant gas checks are still a mystery.

Where to go from here:
-- other than action screw tightness, I am out of ideas with this snug 1/2 degree throat. It does not seem to be as accurate as the original 1 degree throat.
-- the throat experiments so far have demonstrated that small changes in the throat can make a big difference in accuracy, so I am inclined to focus on the throat. This throat was deliberately cut on the tight side and I am worried that it may be too tight, so I may try recutting it just a tiny bit deeper. It's easy to cut it too deep and spoil accuracy, though. If it were a cheap barrel then firelapping would be an option to gradually open up the throat, but I am reluctant to firelap this top-of-the-line barrel.
-- other than using epoxy to glue gas checks on, I don't know what to do about the errant gas checks. Some days it doesn't seem to correlate to anything.

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Re: CBA loads

Postby mtngun » Thu May 11, 2017 8:23 am

In addition to the bolt release sometimes binding against the stock, from time to time the rear tang screw had been difficult to start, as if the hole in the stock was not lining up with the threaded hole in the action. So I inspected the bedding very carefully.

Both measurement and visual inspection showed the holes in the stock to have the same spacing as the threaded holes in the action. But .... when the holes in the stock were lined up with the threaded holes in the action, then the recoil lug was not making contact! :twisted: If I slid the action back so that the recoil lug made contact, then the holes no longer lined up, particularly the hole for the tang screw. So depending on how it was assembled on any given day, either the recoil lug had not been making contact and/or the tang screw was binding and carrying some or all of the recoil forces. I don't know how that came about, but there it was, and it's definitely a no-no.

Fixes:
-- I enlarged the hole for the tang screw, from 0.257" to 0.266".
-- I rebedded the recoil lug with devcon. The rest of the bedding was good (it's not the prettiest bedding job but nonetheless it had aluminum pillars, and devcon in the important places other than the recoil lug issue).
-- since the center screw serves no purpose other than to hold the trigger guard in place, I devcon'd a chunk of aluminum to receive the center screw, and then drilled and tapped it. The center screw will no longer have any contact with the action.
-- I used a pencil grinder to create generous clearance for the bolt release.
Image

I like it when I can identify an assignable cause and then fix it. :) We'll see if the improved bedding makes any difference on the target.

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Re: CBA loads

Postby mtngun » Mon May 15, 2017 8:45 am

This morning I got up at 5 a.m. to lob a few bullets downrange before going to work, to see if the improved bedding helped. In addition to the bedding fix, some other things have changed since the last range session:
-- 10 firelapping rounds were fired with #280 grit, mainly with the hope of knocking down any sharp edges in the throat. The barrel itself was already lapped at the Shilen factory.
-- the nose sizing/seating combo was tweaked slightly so that the bullets did not seat as deep as last time, but still relatively deep, with the gas check approximately flush with the bottom of the neck.
-- a new bullet was tried. It was intended to have a cone nose, but came out misshapen, so I christened it the "Ugly Loverider" (ULR). Aside from the nose it is a typical Loverider.

Here is the Ugly Loverider.
Image

The ULR turned in this barrel's best group to date, and the ALR did slightly better than it's best group last time. 2 groups are not enough to prove much but I'm feeling optimistic that the bedding fix made a difference. :)
Image

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Re: CBA loads

Postby mtngun » Tue May 16, 2017 6:14 am

Shooting at 5:30 a.m. before going to work, to see if yesterday's 0.7" group with the ULR bullet was repeatable. There was a light drizzle and a breeze that constantly changed direction and speed, never more than 10 mph but it kept changing faster than I could change my hold. :lol: Oh well, that's part of the game.

Targets #1 and #2 were shot yesterday, #3 and #4 were shot today.

The flier on #3 happened when the wind reversed direction. I did change my hold to compensate, but perhaps I did not compensate enough.

The flier on #10 felt like a good hold. :?

Note that the dispersion is predominantly horizontal on all three ULR targets. That means it is probably mostly due to wind drift, not the load. If the guy behind the trigger would do a better job of compensating for wind ..... :roll:
Image

Conclusion:
-- the ULR wants to shoot but isn't quite perfect.
-- the 0.98" average for the ULR is good, but no better than this barrel's original 1 degree throat, and not good enough to win CBA matches.

Things to Try Next:
-- while there is always room to improve the load with various tweaks, this basic load is capable of MOA, so I want to focus on bullet designs. The main purpose of this project has always been to come up with the best bullet design.

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Re: CBA loads

Postby mtngun » Fri May 19, 2017 8:54 am

I was behind the bench at 5:30 a.m. to try a new bullet. It was dead calm, but there was some occasional mild mirage.

The new bullet was the same design as the "ULR" from the previous post, except I fattened up the groove diameter on the top half of the bullet, trying to maximize the weight. As a result, the weight was 194.5 gr. compared to 190 gr. for the ULR. Will the resulting shallow grooves affect accuracy? It's a bit of a mystery how grooves work, though in general cast bullets shoot better if they have grooves, even in the case of coated bullets that don't need lube. Besides holding lube, grooves also influence what happens as the bullet is engraved.

In addition to the fatter groove diameter, the nose came out less bumpy than the ULR but still not the straight cone shape that I want. It's tough to lathe bore pointy noses and all sorts of things go wrong. I'll have to keep working on making the cone better.
Image

Target #1: the standard load of 33.4 gr. Leverevolution and the standard size of 0.3085".
Target #2: changed the final sizing diameter to 0.3080" (actually 0.3082" - 0.3083", more on that later).
Target #3: upped the powder charge hoping to hit the 2300 fps sweet spot that this barrel seems to prefer.
Image

Conclusions:
-- the FGLR was less accurate (1.28" average) than the ULR (0.98"). Strictly speaking it takes more than 3 groups to prove a small difference, but in this case the groups were so consistent that I'm inclined to believe that the difference is real.
-- I can't explain the physics of why the deep grooves on the nose shot better than the shallow grooves, I just know that it makes a difference.
-- there has never been any indication of inadequate lubrication with any bullet in this barrel. There is no leading, and the loverider designs hold gobs of lube.
-- the small change in diameter did not seem to make any difference. However, the diameters were not exact because these 35 BHN bullets spring back like crazy. My sizing procedure up to this point has been to apply the gas check and size 0.309" prior to oven treating, then final size in a 0.308" die, which due to spring back, actually results in 0.3085" - 0.3090". To make today's 0.308" bullets I had to use a 0.3075" die and even then size each bullet 3 times which resulted in 0.3080" - 0.3083". Now that I know this throat is happy with 0.3080" - 0.3085" bullets, I may start sizing to that diameter prior to oven treating so that I can get more consistent diameters.

Things To Try Next Time:
-- I may recut this cavity so that the nose is grooveless. That will provide another data point on the effect of grooves on the nose .
-- Otherwise the ULR design seems to work as well as anything, I just need to figure out how to cut a good coned nose. I have a theory as to why a coned nose might be more accurate than a conventional ogive for this application, I'll explain my theory if I ever succeed in cutting a decent CLR (Coned Loverider). :lol:

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Re: CBA loads

Postby mtngun » Wed May 31, 2017 6:06 pm

Continuing the nose groove shootout .... I recut the "Fat Grooved Loverider" cavity so that the nose was solid or nearly so. The idea is to give us another data point on the role of grooves on the nose.

The "solid" nose dropped out of the nose already tapered, and then it was sized in the tapered nose die on the same setting that I used last time.
Image

The solid nose shot poorly, throwing too many fliers. :cry:
Image

Average 10 shot group from best to worst:
-- 0.98" for "Ugly Loverider" with normal depth grooves on nose
-- 1.28" for "Fat Grooved Loverider" with shallow grooves on nose
-- 2.13" for "Solid Nose" Loverider

Conclusion:
Clearly the normal depth grooves on the nose shot best. Now, some people have great luck with "solid nose" spitzer bullets (though commonly using a 2-diameter design rather than a tapered "glove fit" design) so I'm not saying all solid nose cast rifle bullets are bad. I'm just saying that with this particular bullet design, with this particular barrel & load, the grooved nose shot better.

There are still quite a few bullet design tweaks yet to try. My next focus will be to continue trying to cut a good looking straight coned ogive.

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Re: CBA loads

Postby mtngun » Sat Jun 03, 2017 6:59 pm

Now I turn my attention to optimizing the middle of the bullet while continuing to work on perfecting the ogive. Here's a new Loverider bullet -- actually the same basic design that I've been using for a while, only with tweaks here and there.

Three things have changed compared to the "Ugly Loverider" bullet that averaged 0.98":
-- the ogive is more cone-like. It still has a cosmetic flaws but nonetheless it's pretty close to a cone, more on cone-theory later.
-- the weight is reduced to 177 gr., mainly because the cone ogive weighs less than a curved ogive.
-- band #5 (counting from the bottom) used to be a driving band but now it is a bore riding band, hence I call it a "wasp waist" bullet.

The theory behind the cone ogive is that it's BC should be just as good as the same length curved ogive, but the cone ogive will weigh less. That means there is less unsupported weight trying to "tip" the nose of the bullet as it travels through the barrel.

The theory behind the "wasp waist" is that perhaps the bullet does not need much support in the middle, as long as it is supported at both ends?
Image

Well the "wasp waist" bullet was a failure, averaging 2.60". :cry:

Since 3 things changed, which of the 3 things is responsible for the horrible accuracy? I'm going to guess the wasp waist is to blame.
Image

Groups seemed to get worse as more shots were fired so I checked for leading. Meh, just a tiny bit of leading in the corners of the grooves. I wouldn't think it would be enough to worry about?
Image

For next time, I will recut band #5 to be a driving band, and retest.

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Re: CBA loads

Postby mtngun » Wed Jun 07, 2017 6:24 am

I recut the "Coned Loverider" (CLR) so that band #5 (counting from the bottom) is a a driving band rather than a bore riding band. While I was working on it I noticed that there was a machining problem on the original CLR cavity -- everything had been cut 0.015" less deep than it was supposed to be. That wouldn't be a big deal except it left the gas check shank 0.015" too short, not long enough to swallow the gas check, at least not without force. HOUSTON WE HAVE A PROBLEM. Last time I had seated the gas checks by hand and in hindsight the checks were not able to seat completely on the too-short shank. This time I compensated for the too-short shank by seating checks with the lubrisizer and applying a fair amount of force to firmly seat the checks, or so I hoped.

Now we have 3 variables compared to the "ULR" bullet that averaged 0.98":
1) cone ogive vs. "ugly" ogive
2) 178 gr. vs. 190 gr. due to the lighter nose plus 0.015" shorter overall length.
3) too-short check shank vs. good check shank

Here's the CLR after sizing, with band #5 (counting from the bottom) re-cut to be a driving band.
Image

With a 1.87" average for the re-cut CLR vs. 2.60" for the "wasp waist" CLR, clearly the re-cut CLR was an improvement, though still vastly inferior to the 0.98" average of the ULR.
Image

Was the re-cut CLR better because I seated the checks forcefully with the lubrisizer or was it better because band #5 was a driving band? My gut feeling is that band #5 made the most difference, but there's no way to be sure. In hindsight these CLR experiments have been compromised by the too-short check shank, so I will cut a new cavity with a proper shank and re-test. That's frustrating but such is the life of an experimenter.

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Re: homemade reamers for CBA loads

Postby PG1 » Sat Jun 10, 2017 7:00 pm

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



Hi,

Do you have a writeup on how the homemade reamers are fabricated and used? I have seen this "spoon bit" style of reamer mentioned in one of the old classic gunsmithing books -- Howe, The Modern Gunsmith (1941),. Does the full chamber reamer twist at all when cutting the taper?

This style of reamer is interesting for experimenting with different chamber shapes, or as you have done above, changing throat angles. Attraction for me is that it can be made on a lathe only, I do not have a milling machine. I have a tool post grinder however.

Judging by the large knurled knob, it looks like you are holding the reamer by hand, is that correct?

thanks, and keep innovating!

Paul


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