CBA loads

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mtngun
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Re: CBA loads

Postby mtngun » Sat Jun 10, 2017 7:45 pm

No, I don't have a single write-up. My technique has evolved over the years since I started making them.

My basic technique. You'll have to modify to suit your equipment.
-- it's easier (though more work) to make separate reamers for chamber, neck, and throat. Easier in the sense that it is easier to grind and stone, especially the relief.
-- use O-1 drill rod
-- center drill both ends
-- turn pilot leaving 0.010" oversize
-- turn rest of reamer leaving 0.010" oversize.
-- leave a little undersize space between pilot and cutting section, that makes it easier to grind and stone.
-- mill flat but stop at least 0.010" short of centerline.
-- heat treat, quench in oil holding reamer vertically and moving up and down in oil.
-- reamer will warp when quenched. Anyone who says they don't warp is lying. :lol: The 0.010" oversize is to allow for warping.
-- use tool & cutter grinder to sneak up on final diameters.
-- use surface grinder to finish grinding flat to centerline
-- grind relief to within 1/32" or so of cutting edge. I do this more or less freehand on a benchgrinder, but it's tricky. It can also be done on a T&C grinder or toolpost grinder, but the setup takes time.
-- some people claim you don't need relief on a D-bit, but I've tried it both ways and they cut much easier if they have relief, just like any other cutting tool.
-- lightly stone cutting edge.
-- use the stone to slightly dull the non-cutting edge.

No, the reamer doesn't twist, though it may flex along the flat a bit to straighten out any warpage. I consider that a plus.

I've experimented with holding the reamer by hand, other times with a short wrench. Still looking for the perfect way to hold it. If the relief is right, it should cut freely and you should be able to hold it by hand as long as you feed it lightly. The throating reamer in particular desires an extra light feed, otherwise it will "catch" on the rifling and chatter. If force is required to make it "bite," that's a sign that you don't have enough relief somewhere. Paint the cutting edge with a marking pen and look for spots that rub off -- they need more relief.

There's a lot more to it but that should get you started.

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Re: CBA loads

Postby mtngun » Sat Jun 10, 2017 8:29 pm

Continuing our search for the perfect target bullet design .... last time due to a machining error the "CLR" bullet had a too-short check shank that made it difficult to seat the gas check 100%. So I cut a new cavity, same design except this time the dimensions came out right and the check shank was the proper length.

This was intended to be an apples-to-apples test of the coned ogive vs. the ugly somewhat curvy ogive, but as usual there were also some unintended variables:
-- the front band on the ULR looks to be longer than the front band on the CLR, not intentionally but due to normal machining tolerances. The CLR front band is 0.040" long while the ULR front band might be 0.060" long.
-- the front band on the ULR is a little fatter after nose-sizing, 0.3012" vs. 0.3009" on the CLR. That might be due to the nose-die setting or it might be due to the ULR's band being longer and springing back more.
-- the ULR weighs more because its ogive is heavier.
-- the ULR was sized after heat treat in a 0.3084" die so it sprang back to 0.3086" or sometimes as big as 0.3090".
-- the CLR was sized before heat treat in a 0.3084" die so it didn't spring back much, running 0.3080" - 0.3084".
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You would think that the CLR would shoot about the same as the ULR since they are the same design other than the ogive shape? But the the CLR shot poorly.

Group #1 was shot around 10 a.m., in significant mirage. On average the mirage jiggle was 1/4" but it was different for every shot and sometimes all I could see in the scope was a bouncing orange blur. The mirage was definitely affecting accuracy so I gave up after the one group.

Groups #2 and #3 were shot around 6:30 p.m.. The mirage had lessened but nonetheless there was still an average of 1/8" mirage jiggle.
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Conclusions:
-- due to the mirage I don't have confidence in the results.
-- that said, the load never acted like it wanted to shoot one ragged hole.
-- I will retest under better range conditions
-- I will also retest the ULR.
-- When I retest I'll size 0.309" instead of 0.3084".

In general, I am not happy with recent results. I need to figure out what is wrong and fix it.

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Re: CBA loads

Postby mtngun » Tue Jun 13, 2017 6:27 pm

Behind the bench at 5:30 a.m. to retest some loads before the mirage kicked in. There was an intermittent 5 - 7 mph breeze that I attempted to compensate for.

The usual load of 33.5 gr. Leverevolution, oven treated J.R. brand reclaimed shot that normally runs 35 BHN, BAC lube, and Remington #7 1/2 primers. All gas checks were seated with a seater on the lubrisizer prior to sizing in a 0.309" push-thru. Then oven treated, lubed, nose sized, final-sized in a 0.309" push-thru, and seated right at the jam point (where jam is defined by firm thumb pressure pushing the bullet into the rifling). I attempted to adjust the nose die such that the front band came out about 0.3015" because that had worked well in the past.

The .309" diameter was an experiment. The original plan was to shoot one set at .3090", one set at 0.3085", and one set at 0.3080".

All of these bullets had been tested before, so this was simply a retest under better range conditions. BTW, the photo of the ALR shows the 2nd band from the top as 0.3036", but my scribbled notes were hard to read so it could have been 0.3026". :lol:
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The ULR had averaged 0.98" on a previous occasion, but this time it produced a shotgun pattern, as did the other two bullets. Range conditions were pretty good so I had nothing to blame it on. The ALR and ULR groups were shot with a Weaver T36, but for the CLR I switched to a Sightron 36X, just as a sanity check. It still shot a lousy group with the Sightron, so it does not appear that I can blame either scope.

By the way, the CLR group was overlapping a group above it so it may have actually been larger than 2.10". Regardless, even 2.10" is terrible. :cry:
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OK, so my heavy benchrest gun with its spendy top-of-the-line Shilen barrel is shooting like a lever action -- and a lousy lever action at that. That doesn't seem right, does it? What could be wrong?
-- did the switch to 0.309" diameter make it shoot shotgun patterns? That would be hard to believe.
-- switching scopes didn't seem to help.
-- an inspection showed that the bedding fix that I performed a few weeks ago seems to be holding up.
-- I verified that the barrel was torqued on plenty tight.
-- a borescope exam showed nothing wrong,
-- this barrel never has shown much love for its current 1/2 degree throat. Nonetheless, a few weeks ago it was averaging 0.98" with the ULR. 0.98" sounds pretty good compared to shotgun patterns. :lol:

Things left to try?
-- try a few jacketed bullets, as a sanity check on the rifle and scope.
-- try 0.3085" and 0.3080" as I had originally intended. I doubt if it will make much difference, but at least I can rule it out.
-- admit defeat with the 1/2 degree throat and try something else?

If I can't figure it out I may set this barrel aside and do something else for a while to recharge my batteries. :idea:

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Re: CBA loads

Postby mtngun » Wed Jun 14, 2017 10:37 pm

Since last time these things have happened to the rifle:
-- I checked the action screws. They were tight.
-- I removed the barreled action from the stock and inspected the bedding. It looked fine, with the recoil lug making contact when the screw holes were lined up.
-- I verified that the barrel was screwed on tight, then removed the barrel and reinstalled it, using a torque wrench to torque it to 100 ft-lbs as per the recommendation of Jackie Schmidt (a respected benchrest shooter).
-- I did not have an appropriate torque wrench for the actions screws (but I ordered one) so I settled for snugging them up a little tighter than usual.
-- I reinstalled the Sightron 36X scope.

This 30BR has been driving me crazy so out of desperation I did something that I hate-hate-hate to do -- I shot some jacketed bullets through it! :twisted: The same load that I use with cast bullets except I seated the bullets 0.010" away from jam. There was some mid-day mirage averaging 1/8" jiggle, and a 0- 5 mph breeze that I did not bother correcting for. Despite the mirage the cheap jacketed bullets shot a 0.65" group. That tells me 1) there is nothing mechanically wrong with the scope or rifle, 2) my benchrest technique, while not in the same league as the serious competitors, is nonetheless adequate for CBA competition where 10-shot 0.65" would be competitive, 3) sub-MOA is do-able in 1/8" jiggle mirage, and 4) that leaves only my cast bullet loads to blame for the recent shotgun pattern groups. :cry: :roll:
Image

OK, now back to cast bullet experiments ....

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Re: CBA loads

Postby mtngun » Wed Jun 14, 2017 11:07 pm

Repeating the Ogive Shootout, except the 0.309" bullets were resized to 0.3084". Because they are hard bullets that spring back, I had to run them through the 0.3084" die several times to achieve the diameter, and even then there was a lot of variation. I sized the ULR and CLR bullets 3 times and the ALR bullet 4 times. Once I settle on a favorite diameter I'll do the sizing prior to heat treat for more consistent diameters, but in the meantime the multiple sizing passes are a way to deal with the hard bullets.

Everything is the same as last time other than the 0.03084" diameter. The groups were fired from left to right. The ALR shot about as well as it ever has, but the ULR and CLR gave the nearly the exact same ugly shotgun patterns as last time. :cry:
Image

By now I am confused and dazed and don't claim to understand what is going on. :roll: All I know for sure is my name, rank, and serial number. :lol: :lol: :lol:

My only new theory at the moment is what if the problem is bore fouling? I can't see any significant bore fouling with the bore scope and patches come out clean other than carbon, but consider this:
-- the ULR's 0.98" average on May 15 - 16 was shot immediately after 10 firelapping shots. It's first group was 0.7", 2nd group was 1.05", and 3rd group 1.20". Groups opened up as more shots were fired.
-- today's ALR 1.20" group was shot immediately after 11 jacketed rounds. Then groups opened up.

What if there is some slight fouling -- so slight it's not noticeable to the eye yet somehow it's enough to degrade accuracy? What if my normal cleaning routine consisting of 1 patch wetted with Ed's Red at the end of the day does not remove the fouling? What if firelapping rounds or jacketed rounds do remove the fouling and restore accuracy at least for a while?

That theory makes a lot of sense other than I'll be damned if I can detect any fouling! :lol: Next time I'll inspect more closely and clean more rigorously.

And I'll continue the diameter shootout, next time sizing to 0.3080".

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Re: CBA loads

Postby mtngun » Fri Jun 16, 2017 10:55 am

Behind the bench at 5:30 a.m. to continue the ogive and diameter shoot-out. There was no mirage and barely any wind so it was a great day to shoot!

The same load except for two things 1) bullets were final sized to 0.3080" - 0.3083" by running through a 0.3075" push-thru 3 or 4 times and 2) I gave the barrel a good scrubbing with JB bore paste (a mild abrasive) before shooting, and scrubbed with JB again after each group.

The theory behind the JB treatment was that maybe the shotgun pattern problem is due to fouling even though there is no significant leading seen with the borescope and no lead on patches.

One fouling shot was fired after each JB treatment, but sometimes it took 2 or 3 shots before velocities stabilized.

The ALR bullet did so-so. Shot #9 was an outlier, perhaps because the barrel was starting to foul???

The ULR bullet still made a shotgun pattern though somewhat improved compared to the previous ogive shootouts. Shots #9 and #10 were outliers, perhaps because the barrel was starting to foul???

The CLR bullet still made a shotgun pattern though somewhat improved compared to the previous ogive shootouts. Its worst outlier, the low shot, was shot #2 so I probably can't blame that on fouling???
Image

The gas checks had been behaving themselves lately but today it threw one gas check. I'm not sure which bullet caused it or whether that bullet landed in the group.
Image

At the end of the session I borescoped the barrel. The throat area was clean and the muzzle area was clean, but the middle of the barrel looked very dark. This photo has been enhanced to improve the contrast -- before enhancement you could not see anything other than a dark blob. Now you can see that there might be a little grey color in the corner of the groove but that's not something I would consider unusual or worrisome. I'm more worried about why everything is black?
Image

This is the same spot in the barrel after one patch with Ed's Red. Now the lands are cleaner, but the grooves are still dark.
Image

After a dozen or so passes with JB paste. Better, but the grooves are still darker than the lands.
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Thoughts:
-- the big question is why is it shooting shotgun patterns with a load that used to average 0.98" :?: :?: :?:
-- due to the shotgun pattern problem, the ogive and diameter shootout hasn't told us much about which ogive is best or which diameter is best. :lol:
-- there is circumstantial evidence that the shotgun patterns may be caused by fouling -- it shot better immediately after firelapping, it shot better immediately after shooting jacketed bullets, and it shot better after cleaning with JB paste.
-- I'm not confident about the fouling theory, but I don't have any better ideas at the moment. Do you?
-- I have heard reports of carbon fouling destroying accuracy (typically with jacketed bullets), but never personally experienced it. Perhaps I have experienced it now? :lol:
-- if it is a fouling problem, then the next question is what causes it and what to do about it? Is the barrel to blame? That seems unlikely since it is a lapped Shilen. Are the cast bullets to blame? It's possible, but seems unlikely since there is almost no evidence of leading and the 2300 fps velocity should not be a big deal. I'm inclined to suspect the powder, coupled with the moderate pressure (40 - 45 ks) that doesn't allow the powder to burn as clean as it would at max pressure.

Things To Try Next Time:
-- first, get the barrel squeaky clean.
-- give up on Leverevolution for a while, and try different powders.

Again, I'm not at all sure that carbon fouling is to blame for the shotgun patterns. But if the carbon fouling theory is correct, then a good cleaning and switching to a different powder should make a difference.
Image

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Re: CBA loads

Postby mtngun » Fri Jun 16, 2017 7:02 pm

Trying IMR8208 powder, and cleaning in between groups with Ed's Red and a brass brush. Ed's Red and a brass brush seem to clean carbon just as well as JB paste, plus it's easier and faster.

The theory is that if the shotgun patterns were caused by carbon fouling with Leverevolution, then switching to a different powder and cleaning regularly should restore accuracy.

Here's a borecam comparison of Leverevolution vs. IMR8208. To my eye IMR8208 is cleaner, what do you think?
Image

I used a variety of bullets that were leftover from previous tests. Did accuracy improve with 8208 and brushing between groups? On the whole, yes, bearing in mind that I was fiddling around with scope settings and powder charges and a 15 mph wind.

I made a scope adjustment just before shooting target #1. The shots started high and walked down until they finally stabilized. Hence the vertical spread might have been due to the scope adjustment needing to settle in.

You can see the 10 - 15 mph wind's effect on targets #2 and #3.

Target #4 used coated bevel base bullets that had turned in a 2.65" group when I tested them on March 12, nearly the same as today's 2.55" group.

While none of these groups were match worthy, at least #2 and #3 were groups rather than shotgun patterns. I think that confirms the carbon fouling theory.
Image

The good news is that I seem to have figured out the root cause of the shotgun pattern problem, and it can probably be fixed by using a different powder and possibly a different cleaning regimen.

The bad news is that when this barrel was new and had its original 1 degree throat, it shot targets like this from March 19.. Since then, I seem to have gone backwards, not forwards. We'll see if like-new accuracy can be restored now that the carbon fouling problem is nearly resolved. If not, then I may have to admit defeat with the 1/2 degree throat and go back to 1 degree.
Image

Next Time:
-- retest the 3 ogives with 8208 at 2300 fps under good range conditions.
-- if the results are decent, then settle on that load and use it to continue testing experimental bullet designs.

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Re: CBA loads

Postby mtngun » Sat Jun 17, 2017 7:41 am

A good article on cleaning the barrels of benchrest rifles.

Every expert seems to think his cleaning method is right and the other guy's cleaning method is wrong. That sounds a lot like the cast bullet world! :lol:

There does seems to be general agreement that carbon fouling can kill accuracy.
I’ve found that, when a barrel rather abruptly starts grouping real badly–you’ve probably got a carbon problem. ~ Greg Tannel


I'm new to the carbon fouling problem so I don't have a strong opinion on the best cleaning procedure. For now I will monitor the barrel condition closely with the borecam and go from there.

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Re: CBA loads

Postby mtngun » Mon Jun 19, 2017 7:16 am

Behind the bench at 5:30 a.m. again -- no wind, no mirage, YEA!!! 8-)

Today's goal was to retest the concept of cleaning in between every group to remove carbon, and to compare carbon fouling with different powders. The bullet was a 183 gr. Loverider that I had tested before -- I don't think I ever assigned it an acronym, it's just a plain jane Loverider with a sorta secant ogive. It was chosen for the simple reason that I had some sitting on the shelf! :lol:
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The barrel was squeaky clean at the start, then it was cleaned with a brass brush and Ed's Red after ever group. One fouling shot was fired into the main group after cleaning, hence there are 11 shots instead of 10. The idea was that if the fouler went into the group I would count it, but if it fell outside the group I would justifiably disregard it. As it happened all the fouling shots landed inside their group (one of the reasons that I switched to the Loverider design rather than a conventional Loverin is the Loverider seems less sensitive to temperature and needs fewer fouling shots).

I attempted to load each powder to 2300 fps, but didn't always guess the powder charge right so the N133 load was too fast and the RL15 load was too slow.
Image

I borecam'd the barrel after shooting each powder, except I forgot to borecam after 8208, so I had to grab the 8208 borecam from June 16 for this comparison. Yeah, the low-resolution borecam photos leave a lot to be desired, but nonetheless you can see a difference from one powder to the next. To my eye here's how how the powders rank for cleanliness:

1 -- IMR8208 cleanest
2 -- RL15
3 -- N133
4 -- Leverevolution dirtiest

Obviously there are other suitable powders that I am neglecting for the simple reason that I don't have them on hand.
Image

Observations and Things to Try Next Time:
-- today's results removed any doubt in my mind that the shotgun pattern problem was caused by carbon fouling. As long as I keep the barrel squeaky clean, it shoots as well as it ever did (1 MOA).
-- for the time being I will continue brushing between groups, though eventually I'll experiment to see how many shots can be fired before accuracy deteriorates.
-- I would like to retest RL15 with the powder charge increased to deliver 2300 fps. In theory it should burn a little cleaner as the pressure increases.
-- internet legend has it that some powders create "soft" carbon fouling while others create "hard" carbon fouling. That may be but I have no way to prove or disprove it. All I can say is that some powders definitely create more carbon fouling than others.

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Re: CBA loads

Postby mtngun » Tue Jun 20, 2017 3:38 pm

Now that I have some real world BC measurements (see the BC thread) I can estimate the real world wind drift for my loads. The following assumes standard atmospheric conditions. At my local conditions the drift will actually be about 1.5" at 100 yards. Even so, 1.5" is still a lot when you are trying to shoot sub-MOA groups! :o
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