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Re: 6x45 Contender Rifle

Posted: Sun Jan 31, 2016 9:33 pm
by mtngun
Well, I spent several hours typing in a detailed range report with some useful data .... and then somehow hit the wrong button and *poof* it is gone. :cry: Oh well, I'll try again tomorrow.

Re: 6x45 Contender Rifle

Posted: Mon Feb 01, 2016 6:25 pm
by mtngun
Let's try again to post the latest experiments with coated bullets. Now bear in mind that I am not trying "to work up a good load" like most handloaders typically do. I have no practical use for a high velocity CB load and in fact this Contender barrel is soon to be repurposed as a hunting rifle with jacketed bullets. My game is experimenting with cast bullets and trying to figure out what makes them work or what makes them fail. I like to test loads that are right on the ragged edge of failing because I think that makes the load more sensitive to improvements or to disimprovements. And we'll demonstrate that today !
First up, let's try coating bullets with spar urethane instead of ordinary polyurethane. Spar urethane is supposed to be softer and more flexible than polyurethane. I can see how that might possibly be a good thing for bullets or possibly a bad thing. In the meantime note that spar urethane dries slower than polyurethane, and it costs more, so those are two strikes against it.

62 gr. plain base bullets, air cooled WW, sized 246x242, seated 0.006" away from contact, 27 gr. WW760, CCI #41 primer, and HVR lube. Well there were 2 wild fliers -- I'm not even sure which group(s) they go to so I did not count them, but nonetheless the fliers suggest this combination is on the ragged edge of failing. If you ignore the fliers then spar urethane was no more or less accurate than polyurethane. I'm inclined to lose interest in spar urethane as a bullet coating because it doesn't seem to have any advantage to compensate for its disadvantages.

Next, let's see how a harder BHN affects accuracy with polyurethane coated plain base bullets. The wheelweight bullets were oven treated at 475F before applying 3 thin coats of shake-n-dry polyurethane. Today's standard load of 27 gr. WW760, seated 0.011" away from contact, and HVR lube.

Woah ! Half the 25 BHN bullets missed the target completely!

The hard flat base bullets were not quite as awful as the bevel base bullets. This is consistent with our observation that when pushed hard enough, the corner of a bevel base begins to melt and gas cut just a little bit sooner than a flat base, because the corner of a bevel base is exposed to hot gas on two sides while the corner of a flat base is exposed to hot gas on only one side.

At any rate, this coated plain base load does not like hard bullets!

The 25 BHN coated plain base did foul the barrel just a little. Here's one isolated bit of lead:

But the worst of it was toward the muzzle. It wasn't that bad as lead fouling goes, still it was not squeaky clean, either.

Next, let's see if polyurethane coating improves the accuracy of a gas check bullet. Last week's testing suggested that the gas check bullet prefered a hard BHN, so we stuck with 25 BHN for this test. 57 gr. GC spitzer, sized 246x243, 27.6 gr. WW760, #41 primer, 3 thin coats shake-n-dry polyurethane, seated 0.004" away from contact, and the usual HVR lube.

As a control, an uncoated version of the same load was also tested. To my eye it looks like the coated bullets were slightly more accurate, but I'll be the first to say that I didn't fire enough shots to "prove" a statistically significant difference. So I'll try to repeat this shootout next time.

Here's a Taran analysis for the coated gas check:

And for the uncoated gas check:

Other than the slight leading with the 25 BHN coated plain base, all of today's loads left the barrel squeaky clean, even the uncoated GC load at 2733 fps. I don't recall which load this picture went with but it doesn't matter because they all looked the same. :lol: :lol: :lol:

-- I'm narrowing in on shake-n-dry polyurethane as my coating of choice, prolly 3 thin coats. Other coatings work to various degrees but polyurethane seems to have a slight edge. It sticks like glue, is cheap, not too difficult to apply, and shoots as well as anything else I've tried.
-- I've just begun to explore alloy preferences with coated plain base bullets. Forget everything you thought you knew about CB alloys and start over. :D While the ideal alloy for coated PB will depend on the load, in general it likes a softer alloy than uncoated bullets. I.e. at 2570 fps BHN 11 shoots much better than BHN 25.
-- I've just begun to explore coating gas checked bullets. Coated bullets may have a slight accuracy advantage over uncoated at 2700 fps, but I haven't fired enough shots to "prove" it yet.
-- coated gas checked bullets seem to do better with a hard alloy (~25 BHN) at least at the 2500 - 2700 velocity that I've been playing with. In other words, just the opposite of coated plain base bullets. :lol: :lol: :lol:

Things To Try Next Time:

-- more coated vs. uncoated GC bullets, attempt to get enough data to "prove" a meaningful difference.
-- try an even softer alloy with the coated plain base bullets. What is the optimal BHN for coated plain base?

Re: 6x45 Contender Rifle

Posted: Sun Feb 07, 2016 7:46 pm
by mtngun
Continuing our experiments with polyurethane coating and different BHN .....

First up, repeating the test of uncoated vs. coated gas check at 2700 fps. The usual load of 27.6 gr. WW760, #41 primer, sized 0.246" x 0.243" (or 0.242" for the uncoated bullets), HVR lube on all bullets both coated and uncoated, seated 0.005" away from contact.

Off topic but today I tried backing off the case sizing die as much as I dared to see if that would help with the misfire problems I've been experiencing. Contenders have a wimpy ignition to begin with and it's complicated by rimless cases that headspace on the shoulder. If you size the case for loose headspace then you get misfires because the cartridge moves when hit by the firing pin. If you size the case for tight headspace then the action may not lock up 100% and then you get misfires because the hammer grazes the hammer block interlock. You're damned if you do and damned if you don't. :lol: In any event, I had zero misfires with today's snugger headspace, so maybe I finally found the sweet spot?

Here's the target for the gas check bullets at 2700 fps. To my eye the uncoated bullets look less accurate particularly with regards to horizontal dispersion. The coated bullets are tighter horizontally but plagued by vertical stringing. :( But .... the difference between the groups was not statistically significant.

Summary of the mean radius for each of today's gas check loads:
-- 0.84" for coated BHN 11 (only 11 shots)
-- 0.86" for coated BHN 45 (33 shots)
-- 0.97" for coated BHN 25 (10 shots)
-- 1.11" for uncoated BHN 25 (22 shots)

Summary of velocity for each of today's gas check loads. The BHN 45 bullets were the fastest because they have more engraving resistance which increases pressure, just the opposite of why most people think some loads are faster than others.
-- 2659 fps for coated BHN 25
-- 2666 fps for uncoated BHN25
-- 2668 fps for coated BHN 11
-- 2723 fps for coated BHN 45

FYI here is the Quickload estimate for the GC load. Quickload is not the Bible but if the predicted velocity matches the actual velocity then I figure Quickload is pretty close on pressure, too. In this case the predicted velocity was within 20 fps.

Conclusions & Observations for coated GC bullets:
-- I suspect that coated GC bullets are slightly more accurate than uncoated GC bullets at 2700 fps, but the difference is too small to "prove" in this not-so-accurate load.
-- the bottom line is that coated GC bullets did not hurt accuracy.
-- my general takeaway is that coating GC bullets may be worthwhile in a "bad" barrel that is leading, but improvements are minimal in a "good" barrel that does not lead. That makes sense when you consider that a coating does pretty much the same thing as a gas check -- it greatly reduces base melting and gas cutting.
-- one good thing about the coated GC bullets is they did not seem fussy about BHN. Dunno if that is a general rule or merely peculiar to this load & this rifle.
-- this load in particular and warm Contender loads in general have a tendency to string vertically. Perhaps tweaking the powder charge would help, perhaps using the same cases instead of mixed cases would help (!!!) :roll: , but I suspect the Contender action flexes in an up and down direction and that is the nature of the beast. We'll see if the vertical stringing goes away when I switch to a bolt gun.

Next let's test coated plain base bullets with a softer alloy. I used a mystery alloy that someone gave me, they told me it was a muzzleloader alloy with 1% tin, but the density and hardness suggest it has a little antimony in it, too. In any event it averages 8.5 BHN.

Here's the target. The soft coated bullets started out poorly and got wilder as more shots were fired, probably due to fouling.

Did the borescope reveal leading after shooting the soft coated bullets? Only a tiny bit. This is just past the throat, to me it looks like there is some crud in the corner of the groove.

This is 10" past the breach, I dunno what the dark spots are but the bottom line is that it's not squeaky clean.

This is 3" from the muzzle and is squeaky clean.

FYI here is the Quickload estimate for this plain base load. In this case the predicted velocity was only off 20 fps so I figure that's pretty good.

Conclusions and Observations for Coated Plain Base Bullets:
-- so far best accuracy has been with air cooled wheelweight at approximately BHN 11.
-- BHN 8.5 shot wild. BHN 25 shot even wilder.
-- 3 thin coats of polyurethane shoots as well as any other coating I have tried.
-- coating plain base bullets definitely helps at 2000+ fps. It greatly reduces base melting and gas cutting and allowed me to increase the velocity to 2570 fps at 25,000 psi.
-- however, the 2570 fps load seems to be right on the ragged edge of failure and at the moment I don't have any more tricks up my sleeve to improve it.

Things to Try Next Time
-- water based polyurethane. In theory it's the same stuff after it's dried, but water-based may be easier to apply if it dries faster than oil based.
-- as time and money allows I'll test more coatings but at the moment I short on time and money and want to move on to other projects.
-- In the next few days I will post a thread explaining how I apply the shake-n-dry polyurethane, in case you have been wondering. ;)

Re: 6x45 Contender Rifle

Posted: Sun Feb 07, 2016 7:59 pm
by mtngun
FYI here's the Taran results for today's BHN 45 GC bullets. As you can see the dispersion is primarily vertical.