S & W N-frame Project

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mtngun
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Re: S & W N-frame Project

Postby mtngun » Wed Dec 27, 2017 2:27 pm

So far my data seems to say that a short, snug Taylor cone shoots best, so I was not optimistic about this not-so-short and not-so-snug "Intermediate Taylor" cone, but let's try it in the interest of science. :geek:

Here's the control load with the 180 gr. BB. On average, groups were bigger, ES was bigger, and velocity was slower, compared to the "Taylor Junior."
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The 185 gr. Keith made its trial run. Roughly the same accuracy as the 180 gr. BB.
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Cone Summary:
--11 degree cone in no-name: 4" - 6" (lots of variation from group to group and day to day)
--Taylor Jr. in no-name: 3.76"
--Whole Hog Taylor in no-name: 4.58"
--5 degree cone in GM: 4" - 6" (lots of variation from group to group and day to day)
--Taylor Jr. in GM: 3.30"
--Intemediate Taylor in GM: 4.01"

Lessons Learned
-- one lesson I have learned is that boring throats on the lathe is prone to error. :lol: It would be easier to use a piloted reamer.
-- clearly the Taylor Junior's gave the best performance.
-- from now on I will dial in all barrels using the Mitutoyo directly on the grooves in the leade area.

I have one more chunk of the used GM blank so I will attempt to set it up with 0.0072" tenon offset and a very snug Taylor Junior cone. Instead of boring the cone on the lathe, I will make a piloted reamer to cut the cone. Assuming I can pull that off, then I can get back to testing bullet designs. :lol:

That said, if I were a retired millionaire then I would continue testing different cone designs. For example, what would happen if there were no freebore, just a 1.5" or 1.0" degree leade?

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Re: S & W N-frame Project

Postby mtngun » Thu Dec 28, 2017 3:27 pm

I fitted my last chunk of used GM barrel to the M29.

The tenon was offset 0.0070" - 0.0075" as indicated by the Mitutoyo at the leade area (there is some uncertainty because the indicator bounces around a fair amount in the grooves). If I clock the tenon to offset the cylinder's 0.0070" - 0.0075" misalignment then in theory the barrel will end up perfectly aligned with the cylinder. More likely there will be 0.001" misalignment due to various errors but that's still pretty darned good. :)

After cutting and threading the offset tenon, the grooves were dialed in with the Mitutoyo at the leade area and a 5 degree taper mill was used to quickly create a chamfer at the entrance of the cone.
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I found a 1.5 degree throat reamer in my collection, leftover from the Contender Carbine project, so I used it to cut the rest of the cone. It does not have a straight freebore so the resulting cone is all taper.
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The homemade reamer cut like butter and the resulting cone was smooth and concentric.
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Here's how the 180 gr. BB fits in the "Mini" throat -- it goes in 0.040" or so deeper than the "Taylor Junior," so maybe I should not have called it the "Mini," but oh well the photos are already labeled so we're stuck with the "Taylor Mini" name. :lol:
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Here is a sketch of the as-machined dimensions as best I could measure them with gage pins. Even though the reamer was marked 1.5 degrees, it actually cut 1.15 - 1.30" degrees.

This "Mini" Taylor is very very similar to the two "Taylor Juniors," so I suspect it will shoot about the same as the Taylor Juniors. The difference is that this barrel will have better alignment and this cone is perfectly concentric, so that might help a little bit.

I hope this concludes my experiments with forcing cones, but if for some reason it doesn't, I left the barrel 1/4" long (8 1/2") so that if need be I can set it back 1/4" and recut the cone one last time. I don't have any more 357 barrels laying around and this project is running out of time and money, so it better work! :lol: 8-)
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Re: S & W N-frame Project

Postby mtngun » Sun Dec 31, 2017 7:25 pm

Trying out the inappropriately named "Mini" Taylor throat.

The Keith bullet was pushed by 15.3 gr. WC297 while the rest of today's loads were pushed by 15.6 WC297.

Normally I use the coated 180 gr. BB as a control load, but I didn't have enough of those bullets on hand so I subsituted various other bullets which have a history of shooting about the same size groups as the 180 BB.

All of today's loads were crimp-less, more on that later.

A few good groups were shot, but also a few lousy groups. Consistency was lacking. :cry:
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OK, so the "Mini" Taylor was disappointing. 4.27" at 100 yards is good hunting accuracy, but inferior to the Taylor Junior's 3.30", especially considering that the Taylor Junior cone was off center ! The machining work was very good on the "Mini" cone so the problem must be the design of the cone.

Two theories"
-- the "Mini" Taylor is actually longer than the Taylor Junior. Previous tests have demonstrated that accuracy deteriorates when Taylor throat is made longer.
-- the "Mini" Taylor is all taper, no straight freebore. While I don't think that's a problem, I can't rule out the possibility that a straight freebore helps the bullet in some way.

So I will shorten the cone by setting the barrel back one or two threads.

If I ever get the cone issue sorted out, I plan to do a crimp shootout. In the meantime today's crimpless loads averaged a 43 ES, which is as good as this gun has ever done.

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Re: S & W N-frame Project

Postby mtngun » Thu Jan 04, 2018 11:39 am

I set the GM #2 barrel back 2 threads (0.056"), but left its cone alone other than cutting a minimalist 5 degree chamfer at the entrance. Basically, it's the same cone as before except shorter and tighter. I'm calling this the "True Mini" Taylor cone as opposed to the previous "False Mini" that was actually a "Midi." :lol:
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Despite the long gentle leade, the bullet doesn't have to jump very far to engage the rifling. I'm counting on good barrel-to-cylinder alignment to make this minimalist cone work without shaving lead.
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Bullet fit in the cone before and after setting the barrel back 2 threads.
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This "True Mini" cone is plenty short and plenty snug. It does lack the straight freebore section of a conventional Taylor throat -- I don't know if that matters, but I guess we'll find out.

I hope the "True Mini" is successful, but if it is not, I have several options lined up:
-- firelap the cone.
-- add a short straight freebore.
-- if all else fails I still have about 0.200" extra barrel length to play with in case I need to set it back yet again and try yet another cone design.

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Re: S & W N-frame Project

Postby mtngun » Fri Jan 05, 2018 5:25 pm

Testing the "True Mini" Taylor cone with the same control load used to test all the other cones.

-- its 3.52" average was about the same accuracy as the two "Taylor Junior" cones.
-- the "True Mini" was definitely an improvement over the "False Mini", which was actually a "Midi" cone.
-- in general, reducing the jump to the rifling improves accuracy.
-- in general, making the cone diameter a snug fit improves accuracy.
-- in general, a gradual transition into the rifling improves accuracy.
-- in general, the traditional 11 or 5 degree forcing cone is too abrupt for optimal accuracy (and often too sloppy, too).
-- in general, the traditional Taylor Cone with its long freebore is too long for optimal accuracy, though still an improvement over the factory cone.

The catch is, how do you create a "gradual transition" while at the same time minimizing the jump and minimizing the clearances? :?:
Image

I would like to do more experiments with more cone designs, but I'm going to put that on hold for a while so I can get back to testing bullet designs, crimps, alloys, etc..

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Re: S & W N-frame Project

Postby mtngun » Fri Jan 05, 2018 5:33 pm

Testing the "bastard" bore riding 180 gr. GC bullet.

I forgot to number the sequence of these targets but I started at the top left and worked down to the bottom right.

The first two targets were decent, but targets #3 and #4 were shotgun patterns. What the heck? I examined the gun closely and discovered that the 2 screws attaching the "cheater sled" to the shroud had rattled loose and were allowing the sled to rattle and wobble. After tightening the loose screws, accuracy returned to normal.

With a 3.49" average at 100 yards, the bore rider equaled the 180 gr. BB control load. I think the bore riding nose shows some potential and it would be worthwhile to replace the "bastard" design with some better designs, and also try tweaking the powder charge.
Image

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Re: S & W N-frame Project

Postby mtngun » Fri Jan 05, 2018 5:47 pm

Testing the 185 gr. Keith bevel base. 100 yards, "True Mini" cone.

Accuracy was poor, averaging 7.33". The Keith did not seem to like the "True Mini" cone. :cry:

Previously, the Keith had shot 4.40" in the "intermediate Taylor" and 4.90" in the "False Mini". At no point was it a tackdriver, so I have to conclude that this Keith bullet is a dog. I've never been a Keith bullet fan but had to try it just to say I tried it. :|
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Re: S & W N-frame Project

Postby mtngun » Sun Jan 07, 2018 2:54 pm

CRIMP SHOOTOUT using the 180 gr. BB control load.

Neck tension can influence the case's grip on the bullet even more than crimp. Many expander spuds are too big for my taste and end up getting modified so that they barely touch a sized case.
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A homemade die was used for the roll crimp, and I adjusted it for a "moderate" crimp.

The Lee collet crimp was also set up for a "moderate" crimp.
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The "no-crimp" loads were tested last time. Here are the roll crimp results -- worse than the no-crimp control load in every respect, though 4 groups is not enough to "prove" the difference is mathematically significant.

There was some overlap between the two groups on the right and I wasn't positive which bullet holes went with which group, so the bullet hole with the question marks did not get counted. If I had counted that mystery hole then the average group would have been even worse. There were two many fliers with the roll crimp. :cry:
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Here are the Lee collet crimp results -- nearly identical to the no-crimp control load in every respect.
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The differences were small and not necessarily significant, but since I need to choose one I will choose no-crimp since it is the least work and shoots as well as anything.
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Re: S & W N-frame Project

Postby mtngun » Sun Jan 07, 2018 3:14 pm

As if I did not have enough things to worry about, there's this. :?

The end of the barrel is square and true, and the other two barrels yield similar results, so the barrel is not to blame. The problem is that there is angular misalignment between the cylinder and the barrel.

UPDATE: I measured the cylinder relative to the frame window, using feeler gages and calipers. As near as I can tell the cylinder is sitting square relative to the frame window.

Then I measured the end of the barrel relative to the far end of the frame. The distance from the top of the barrel to the far end of the frame was a few thousandths less than the distance from the bottom of the barrel to the far end of the frame. Mind you, I have no way to know whether the frame surface that I was measuring against is perfectly straight or perfectly square -- probably not. Nonetheless it was the best I had to work with, and it seems to confirm that the barrel is cockeyed relative to the frame..

Since I am confident the barrel was machined square and true, the process of elimination suggests that the receiver threads are cockeyed. If so, that is a common problem in rifles so I'm not surprised that it shows up in revolvers, too. Rifle receiver threads can be trued by cutting them slightly oversize either in a lathe or with a piloted tap, but I've never heard of anyone doing that to a revolver. It would be darned tough to accurately fixture the revolver in a lathe and in any event my lathes don't have the ability to accurately pick up an existing thread. That leaves the possibility of a piloted tap. Well, the only thing available to guide the pilot would be the cylinder holes, so I guess I could make a custom oversize tap with a 0.358" minus pilot, but it would be a lot of work with no guarantee that it would come out right, and then yet another barrel would be required to fit the oversize threads. All in all it would be a lot of work and a fair amount of risk of screwing up the frame so I'm not feeling any enthusiasm for it. :?
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Re: S & W N-frame Project

Postby mtngun » Tue Jan 09, 2018 3:05 pm

Since the 180 gr. bore riding GC shot decent even though it was a "bastard" design, I want to try some more bore riding designs, so here's a couple of new bullets to play with, er, I mean test.

The new bullets have a crimp groove in the right place even though I'm not planning to crimp them. If nothing else the oversize crimp groove acts as a shock absorber when the nose slams into the rifling.

The bore riding section was made longer with the hope that it would not have to jump so far to contact the rifling, but I will show later how that did not work as planned.

The front band length was chosen so that the front band would nearly make contact with the cylinder's ball seat when the cartridge was chambered, and that did work out.

The bore rider drops out of the mold at 0.3474"+ but then the coating brings it up to 0.350"+ depending on how thickly you apply the coating -- I aim for 0.001" thick but don't always hit it. At this point I don't know if 0.350" it the optimal diameter.

Previous tests with different bullet weights showed that accuracy improved as weight increased up until 180 gr., then remained the same with 190 gr. and 200 gr. bullets, but just to cover all bases I'm going to try a 220 gr. bullet. :o

I went with a bevel base because that's what the 180 gr. BB control load uses. So far the coated BB bullets seem to be just as accurate as a GC in this gun, but that may be because I haven't been pushing the BB that hard. If these BB bore riders work well then I may try GC designs, too.
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If you drop a sized bullet into the chamber it comes to rest like this, with the front band making contact with the ball seat. The chamber throats are 0.3580" and I size the bullet in a 0.358" die, but due to spring back the bullets end up 0.3583"+, so they can't be pushed through the throats with finger pressure contrary to the popular rule of thumb that I have rarely followed (about 0.0005" clearance is required to push through without force). The nice thing about the bore riding design in a revolver is that when properly done it results in this perfect fit yet chambers reliably without having to do any fancy nose sizing.
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As mentioned earlier the hope was that the longer bore riding section would grab the rifling in the forcing cone, but instead the front band is the first thing to make contact with the forcing cone. That's because of the very gentle 1.3 degree leade angle. If I had to do it over I might go with a 3 degree leade angle, but oh well. :roll:

If I cut the bore rider oversize, say 0.355", then it would probably make contact with the rifling before the front band. Maybe I'll try that eventually. As I said before, at this point I don't know which diameter is optimal for the bore rider. Cast bullets don't always behave the way we think they should behave so sometimes all we can do is try different things and let the gun tell us which works best.
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