S & W N-frame Project

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mtngun
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Re: S & W N-frame Project

Postby mtngun » Sun Dec 10, 2017 5:49 pm

Next, trying different powders and powder charges with the revised 180 gr. BB

Trying a lighter charge of WC297. Something seems wrong because I used to get 4" groups with the coated 180. :x
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I rarely use 4227 in revolvers because other powders give better velocity. But 4227 tends to be a forgiving powder and cast-friendly, so I gave it a try with the 180 BB. Ho-hum accuracy and high ES. :cry:
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Re: S & W N-frame Project

Postby mtngun » Sun Dec 10, 2017 6:08 pm

The various 180 gr. GC's have been the most reliable peformers in this gun, so surely I can find a pet load for it?

15.6 gr. WC297, CCI 550, R-P cases -- 6 in 5.8" :cry: , 1357 fps, 51 ES.

15.9 gr. WC297, CCI 550, R-P cases -- 6 in 6.2" :cry: , 1376 fps, 83 ES.

That taught me that something must be wrong, because this gun started out shooting 3" - 4" groups with GC bullets but now groups have doubled to 6". :x :evil: :cry:

Since this project started I have done several tweaks that have been beneficial:
-- ES was reduced by segregating cases and switching to CCI 550 primers.
-- adding the "cheater sled" made the gun much steadier.
-- the revised bullet designs deform less when slammed into the rifling.

And yet groups have gotten worse, not better?

One thing that I know is wrong --- bullets recovered from the water tank are engraved unevenly, which definitely hurts accuracy. Some of them definitely have more than the anticipated 0.0015" mis-alignment, so I'm going to focus on the barrel-to-cylinder alignment issue. I have a theory and a plan, but it's complicated so I'll hold off on explaining it. In the meantime I will doublecheck the alignment measurements and go from there.

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Re: S & W N-frame Project

Postby mtngun » Mon Dec 11, 2017 11:45 am

The last time I attempted to measure the barrel / cylinder misalignment, I was seeing 0.0015" misalignment using a tenon stub that was offset 0.005". From that I estimated that the true misalignment was 0.006"- 0.0065" and I cut the barrel tenon with 0.006" offset.

Today I made a tenon stub with 0.0065" offset (or another way to put it is 0.013" runout on the test indicator) and measured again.
-- 3 holes would take a 0.357"+ gage pin part way, and a 0.356"+ gage pin all the way
-- 3 holes would not take a 0.357" gage pin but would take a 0.356"+ gage pin

The 357"+ gage pin was still rubbing on the same side of the cylinder where it has always rubbed, approximately 3:30 o'clock as viewed from the muzzle.

Based on today's measurements, I currently estimate that the misalignment is 0.007" - 0.0075", so in hindsight my original estimate of 0.006" misalignment was not enough.
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Also, when I roughed the barrel I had not anticipated needing to offset the tenon -- that idea came later -- so I had turned the diameter to 0.676". The tenon is 0.670" x 36 tpi, so that only left 0.003" of excess metal on either side of the bore to work with, assuming the roughed barrel was concentric with the bore. Well, when I went to finish the barrel, I realized that 0.003" of excess metal was not going to be enough to give me 0.006" offset. :oops: The math did not add up! All I could do was going ahead and dial in the bore with 0.006" offset and hope for the best. In theory it might have worked, but in theory it might not have worked, depending on thread tolerances.

Fast forward to the most recent water tank test where some of the bullets showed significant misalignment. The explanation is 1) the intended 0.006" offset was not enough and 2) there was not enough excess meat on the roughed barrel to properly create 0.006" offset on the tenon, anyway.

So this barrel is unsatisfactory. No biggie since I only paid $15 for it years ago and I rescued it from the scrap bin for this project. Plus, I have one last mission for this barrel -- I've always wanted to try a Taylor throat and this barrel with its known misalignment should make an appropriate guinea pig. If the Taylor throat is a failure, that's no big deal because I have already decided this barrel is scrap.

Plan "A" is to recut this barrel with a Taylor throat.

Plan "A.2" is to cut yet another barrel, this time with the tenon offset 0.007". This is a budget project -- if I wanted to throw money at it it would make more sense to fabricate a line-indexed cylinder -- so purchasing a new barrel is not going to happen at this time. However, I have a Green Mountain barrel on the 357 TC Carbine. That barrel has been rode hard and put away wet, and has pitting and erosion near the throat, and I haven't shot it in years, so it is an eligible candidate for salvaging. I'll cut off the eroded portion and make a new barrel blank from the remainder.

Bear in mind that even if I cut the tenon offset just right -- 0.007" or whatever the true misalignment is -- there is still no scientific way to clock the offset tenon -- I simply mark the offset point and clock it by eyeball. Also, there seems to be 0.0005" or so variation from one cylinder hole to the next, so even if do everything right, there could still be 0.001" -- 0.0015" misalignment. This offset tenon trick is never going to result in perfect alignment, but the goal is to end up with better alignment than the factory setup.

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Re: S & W N-frame Project

Postby mtngun » Mon Dec 11, 2017 12:51 pm

My version of a Taylor throat. It's relatively short as Taylor throats go, actually no longer than some factory forcing cones. There is no rulebook on dimensions for Taylor throats that I am aware of, so I just did what made sense to me.

Here is how I cut it:
-- first a 0.362" diameter section that goes in 0.110" deep.
-- then an 0.050" long angled transition to 0.358" diameter that is complete at 0.160" deep.
-- then a straight 0.358" diameter section 0.050" long, ending at 0.210" deep
-- then an angled transition to 0.346" diameter at .310" deep.

Whether the way I did it is the right way is anyone's guess. :lol:

With the original throat, the bullet was forced to "turn a sharp corner" to make the transition from throat to the misaligned barrel. Now it still has to turn a corner, but the corner is not so sharp. Perhaps the gentler turn will deform the bullet less than the sharp turn, but there still will be deformation. If you want to minimize the deformation, I would imagine the Taylor throat would need to be as long as the bullet?
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Re: S & W N-frame Project

Postby mtngun » Mon Dec 11, 2017 1:09 pm

Is the tenon of factory barrels concentric with the bore? HELL NO! :lol:

I put the original 44 barrel in the lathe and dialed in its bore, then measured the runout on the tenon in a couple of places. The tenon shows about 0.018" runout (0.009" offset) relative to the bore. That offset could either add or subtract to the cylinder's misalignment, depending on how it clocks. I never attempted to measure the misalignment of the 44 cylinder so I don't know how much it had relative to the frame, or which way it clocked.

Anyway I thought this was an interesting tidbit of information that gives revolver owners something to think about.
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Re: S & W N-frame Project

Postby mtngun » Tue Dec 12, 2017 11:55 am

The used Green Mountain barrel was taken off the Contender Carbine and born again as a barrel for the M29-357.

The barrel tenon has 0.0072" offset.

The forcing cone has a 5 degree per side taper that starts out at 0.361" diameter. The 0.361" entrance will only work if the barrel-to-cylinder alignment is within 0.0015", and I figure it should be.

Barrel-to-cylinder gap is 0.0015" with the offset tenon properly clocked.

GM barrels are nominally 0.356" x 0.346", but this one had been firelapped extensively while on the Contender Carbine, and now measures 0.3561" groove x 0.3475" bore (firelapping affects the lands more than the grooves, as I found out).
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Re: S & W N-frame Project

Postby mtngun » Sat Dec 16, 2017 3:36 pm

Some Starline brass showed up for this project. It's uniformity seems run of the mill.
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Re: S & W N-frame Project

Postby mtngun » Sat Dec 16, 2017 4:11 pm

Same barrel and same loads as last time, only now the barrel has a short Taylor throat aka "Taylor Junior."

Average for all 4 groups was 3.76", much better than last time, though no better than this barrel did when it was new.
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It takes more than 4 groups to prove anything but it seems to me that the Taylor throat made this barrel perk up, especially with the bevel base bullet.

There's a few more things I want to try with the Taylor throat before I move on to the GM barrel.

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Re: S & W N-frame Project

Postby mtngun » Sun Dec 17, 2017 12:25 pm

Continuing to test the No-Name barrel with the "Taylor Junior" throat. All of today's groups were shot with the same coated 180 gr. BB load and new Starline brass, except for 2 groups with annealed R-P brass.

Groups #1 and #2 were shot yesterday.

Groups #5 and #6 used annealed R-P brass. The annealed brass doubled the velocity variation -- it acted like the brass was too soft. Is it possible to over-anneal brass? Velocities were lower, suggesting to me that the soft necks could not grip the bullet tightly. I annealed the necks with a propane torch while the bases stood in about 3/8" of water, then tipped the case over into the water once the neck seemed hot enough. Perhaps next time I will try dunking the neck in 800F lead instead of using the propane torch?

Overall, I consider the Taylor Jr.'s 3.73" average accuracy an improvement over the original 11 degree throat. I am not claiming the Taylor Jr. is the ultimate revolver throat, only that it was a step in the right direction.
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Then I shot the same load with the Green Mountain barrel and its 5 degree throat. Averaging 5.1", the GM barrel was inferior to the No-Name "Taylor Jr." even though I believe the GM has better barrel-to-cylinder alignment.
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Let's review what I have learned so far in this project:
-- segregating cases improved velocity variation a lot.
-- CCI #550 primers improved velocity variation with WC297 compared to WSPM primers.
-- coated bullets sometimes -- but not always -- shoot slightly better than uncoated bullets. In no case has a coated bullet shot worse than its uncoated counterpart. When in doubt, coat.
-- quenched coated bullets shot better than air-cooled coated bullets.
-- a "Taylor Junior" throat shot better than an 11 degree throat.
-- annealed R-P cases doubled velocity variation, though perhaps my annealing technique was at fault?
-- switching to a barrel with what I believe is very good alignment did not improve accuracy noticeably.

Where do I go from here:
-- when the weather cooperates, I would like to test these two barrels in the water tank.
-- after the water tank test, I may want to try a Taylor Junior throat in the GM barrel.
-- try a "Taylor Senior" in the No-Name barrel?

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Re: S & W N-frame Project

Postby Bob » Sun Dec 17, 2017 4:54 pm

Dan, your research & development are second to none! You're doing things that most people would love to do, if they had the resources.

This is fantastic!


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