S & W N-frame Project

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mtngun
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Re: S & W N-frame Project

Postby mtngun » Thu Dec 07, 2017 11:56 am

200 gr. GC, oven treated reclaimed shot for ~35 BHN, pushed by 14.0 gr. WC297 for perhaps 1327 fps.

The two photos are opposite sides of the same bullet.

At first glance the engraving appears to be equal, but a closer look under the microscope suggests that the top groove has been largely wiped out at point #1 but not on the opposite side of the bullet at point #2.

This bullet had a single bore riding band at point #3, and it did its job, engraving slightly all around while the adjacent lube grooves survived largely intact.

As with the other gas check bullets, the gas check fit somewhat loosely as the bullet dropped from the mold; nonetheless it remained firmly attached.

My takeaway from this bullet is that either the top half of the bullet should have had a bore riding band or two, or else the grooves on the top half of the bullet should have been bigger to help absorb the metal displaced by slamming into the forcing cone.
Image

General Conclusions From the Water Tank:
-- to the naked eye bullets appeared to be evenly engraved, but closer examination under a microscope showed that one side of the front band was usually engraved a wee bit more than the opposite side.
-- hence the cylinder-to-barrel alignment is not perfect. I have no way to measure the alignment with the barrel installed but after looking at these bullets I would guess there is 0.002" misalignment. That's far better than the typical mass produced revolver but it falls short of a line-bored revolver.
-- With these 25 - 35 BHN bullets, grooves on the top half of the bullet were often wiped out or nearly so, while the grooves on the bottom half of the bullet survived in decent shape.
-- with these 25 - 35 BHN bullets, the need for a bore riding band or for larger lube grooves or larger crimp grooves is greatest on the top half of the bullet. It's not clear that there is a need for bore riding bands or for larger lube grooves on the bottom half of the bullet.
-- sometimes the bore riding band obturated but other times it did not, depending on the BHN, the load PSI, and the location of the bore riding band.

Well, some of the results were the opposite of what my theories predicted -- that's why I do tests instead of relying on armchair theory. :ugeek: When I am wrong, I try to admit I am wrong and change my thinking. As time allows I will revise my bullet designs.
Image

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Re: S & W N-frame Project

Postby mtngun » Thu Dec 07, 2017 1:28 pm

Before doing the water tank tests, I had re-cut one of the bore riding bands on the 190 gr. GC Loverider. The water tanks tests taught me that, as it turned out, I re-cut the wrong band. Oops! :oops: Oh well, as long as it is here I might as well try it.
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To deal with the wobbly muzzle, I screwed a 3" wide sled (leftover from the Contender Carbine project) to the barrel shroud. The sled adds 12 ounces of weight to the muzzle, bringing the total weight up to 5 pounds even, and of course its width improves stability. I feel guilty for "cheating" with the sled but this project is mainly about testing bullet designs, not testing my rusty revolver shooting skills.
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To deal with the velocity variation problem, I loaded only R-P cases primed with CCI #550, which had showed promise last time. However as luck would have it the antique 20GB hard drive died on the shooting shack computer and I can't view the chronograph screen without the computer's webcam. Sigh. :roll: I ordered a slightly less antiquated replacement hard drive but int the meantime I feel naked shooting without a chronograph. :lol:

Anyway, I shot two groups with the re-cut bullet. The first group was a decent 3.35" at 100 yards, but the second group was a sucky 5.3", with a completely different POI relative to the aiming point. However, the light had changed on the second group so that the aiming point was in the shade while the rest of the target was in blinding sun. Also I experimented with a different benchrest position for the cheater sled on the 2nd target. So all in all there were too many variables and not enough data to prove anything.

Some of the bullet holes seemed to have a bit of a "tail." The bullets have plenty of spin and I did not notice a tail on the original 190 gr. Loverider. The target backer is well-perforated and due for replacement so that might affect the bullet holes, too.

The only thing I can say for sure is that the gun did not wobble nearly as much with the sled. It may take further experimentation to optimize benchrest technique with the sled.
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The jury is still out on the sled, on the CCI#550 primers, and on the re-cut bullet. But based on the water tank tests I have already decided to go back to the drawing board on the bullet design.

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Re: S & W N-frame Project

Postby Brad » Thu Dec 07, 2017 5:03 pm

The deformation on one side being more severe than the other is something I know well!

I will be watching to see what you make for changes in bullet design. I wonder if a bore ride band at the start of the nose followed by a full diameter band wouldn't be a good idea.

I really like the bore ride band in the body of the bullet. It gives displaced lead a place to go.

Keep up the good work Dan. This is very interesting to some of us.

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Re: S & W N-frame Project

Postby mtngun » Thu Dec 07, 2017 6:08 pm

Brad wrote:The deformation on one side being more severe than the other is something I know well!


I've now seen enough of these to be confident that the uneven engraving is due to barrel/cylinder mis-alignment.

Hard to say about bullet design. Cast bullets don't always behave the way we think they should behave.

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Re: S & W N-frame Project

Postby Brad » Fri Dec 08, 2017 2:00 pm

Have you considered firing groups using only one of the chambers that does line up well? Compare it to one that doesn't and see if you get group size differences. I wonder if one group would form in a different location relative to POA?

My Super Redhawk suffers from misaligned chambers as well. I did reduce the groove deformation with a much harder bullet but it still suffered from the misalignment.

I now can see why people pay for an FA

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Re: S & W N-frame Project

Postby mtngun » Sat Dec 09, 2017 8:44 am

Brad wrote:Have you considered firing groups using only one of the chambers that does line up well?

Alignment or lack thereof is similar on all chambers, differing by perhaps 0.001" or so.
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This exercise made me recall my experiences with Dan Wesson revolvers back in the 1980's. In those days I did not have machine tools but my guess is that the tenon on Dan Wesson barrels was probably not concentric with the bore since it was mass produced in a cost-conscious manner. If the tenon was not concentric, then screwing the barrel in or out to adjust the barrel / cylinder gap would have changed the alignment. There was probably some luck involved in happening to have a Dan Wesson barrel that lined up just right when the barrel / cylinder gap was set with a feeler gage.

When I have time I want to chuck the M29's original 44 barrel in the lathe and check to see if its tenon is concentric with the bore. In the meantime some quick and dirty measurements with a gage pin & caliper suggest that the tenon may be off by 0.008". The OEM tenon's misalignment could either add or subtract to the frame's 0.006" misalignment, depending on which way it clocks, and as it turns out it adds, so total mis-alignment would have been on the order of 0.006" + 0.008" = 0.014" !!! :o :shock: :evil: No wonder that 44 was unsatisfactory with cast bullets !

When you think about all the obstacles a revolver bullet has to overcome, it's amazing that they shoot as well as they do. There's probably some luck of the draw when you buy any mass produced revolver -- one might roll off the assembly line with decent tolerances while the next one might be a lemon.

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Re: S & W N-frame Project

Postby mtngun » Sat Dec 09, 2017 7:47 pm

Trying some slightly different bullet designs. Based on the results of the water tank tests I eliminated the bore riding bands and put more and bigger grooves on the top half of the bullet.

First up, a 190 gr. GC. The 0.090" long crimp groove is overkill for crimping, but it is intended to also act as a "shock absorber" that gives displaced lead somewhere to go when the bullet slams into the forcing cone.
Image

FYI I photoshopped today's target images to clean them up and make them easer to understand.

The 190's first group (top left) put 5 shots into 1.1". But a second group with the same load (top right) was ho-hum.

Switching to Federal 200 magnum pistol primers (bottom left) gave slightly slower velocity, about the same ES, and a ho-hum group.

Going back to CCI 550 primers and increasing the powder charge (bottom right) resulted in an uninspiring group.

The good news is that using CCI 550 primers and R-P cases seems to bring the ES down to a tolerable but still not great 52 ES, compared to the 70 - 80 ES I was getting with mixed brass and WSPM primers.

The Federal primers were OK but no better than the 550's.

Increasing the powder charge may hurt accuracy.

The three 15.9 gr. groups had mostly vertical dispersion despite decent ES, making me suspect that my grip and my benchrest technique may be to blame. I'm definitely rusty at wheelgunning and I'm still not that comfortable with my benchrest set up. Since adding the "cheater sled" the crosshairs look good when the gun goes bang, leaving consistent grip the remaining thing that needs improvement. It doesn't help that I have to release the gun between shots in order to type in chrono data. Perhaps once I am satisfied with a load's chrono results I should try shooting a group without releasing the gun between shots?
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Next, a 180 gr. coated bevel base. This is nearly the same design as the 180 BB I have tested previously, the difference being adding the big-ass crimp groove and getting rid of the bore rider band.
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The first group with the 180 was uninspiring, and I was running short on daylight, so I did not shoot more groups with the 180. But it's possible that I was to blame for the fliers, or it's possible that the powder charge may be a little too warm for a plain base bullet, even if it is coated. Next time I may try again with a lesser charge.

The good news is the ES was a decent 52 fps with R-P cases and CCI 550 primers.
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Next, a revised 140 gr. GC, this time with the crimp groove stretched to 0.070", designed for seating out to 1.612", and no more bore riding band. There is no lube groove other than the check shank, and I wasn't sure if that would be enough lube, so I coated a few of these bullets as a fail-safe measure.

I am attracted to this bullet weight because Quickload thinks it can safely reach 1800 fps from a revolver -- that would make for an impressive "Whitetail Whacker." :o :shock: :mrgreen:
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I switched to WW296 for the 140 gr. bullet because I figured the faster burning powder would be more appropriate for the light bullet. But WW296 did not burn well -- velocity was well below the predicted 1800 fps, ES was high, and it produced a big ball of fire! :twisted: :o

Nonetheless the coated version turned in middlin' accuracy, with 3 bullets touching -- it acted like it was trying to shoot despite the poor powder burn. My webcam software was acting up during that string so it only recorded 3 shots -- for what it was worth the 3 shots had a 56 fps spread.

The uncoated version made a bigger pattern, was 45 fps slower, and had 105 ES. A single group is rarely enough to prove anything, but I'm leaning toward the coated version of this bullet.

While 4 MOA will not win target matches, consider that it's minute-of-whitetail-heart and better than most of us can hold under field conditions.

Since WW296 did not burn well, I will make a note to retest the coated 140 with WC297 and perhaps with 2400.
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In general, the revised designs turned in about the same 6-shot groups as their original designs, but at least the revised designs sometimes acted like they were trying to shoot if the guy behind the trigger would do his part. I'll try to follow up with load tweaks and water tank tests.

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Re: S & W N-frame Project

Postby mtngun » Sun Dec 10, 2017 1:39 pm

Today I tried various powder tweaks and got the usual uninspiring 4" - 6" groups. :oops: :cry: :twisted: I'll post the boring deets later.

Right now let's look at the water tank results with the "revised" bullet designs having more and bigger grooves on the front end.

The more and bigger grooves on the front end did their job, but one side of the bullet engraved more than the other side. :oops: :cry: :twisted:
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Again, one side of the bullet engraved more than the other side. :oops: :cry: :twisted:
Image

Not so bad, but to my eye the side in the bottom of the photo is engraved just a wee bit deeper than the side in the top of the photo.

Note that the check shank is still full of lube on this 140 gr. bullet, but the 180 and 190 lost most of their lube. Maybe higher velocity somehow helps the bullet retain lube in the water tank?
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I thought that the offset tenon had corrected the misalignment to within 0.0015" or so, but some of these recovered bullets seem to have more than 0.0015" misalignment ??? :|

I'm confused about why the bullets seem to be more misaligned that I anticipated, but at any rate, this gun is not going to be a tack driver with bullets engraving unevenly like this. Those bullets will be unbalanced and will wobble when they exit the barrel. :cry: I see a line-indexed cylinder in my future, unfortunately that future is a long way off. :lol:

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Re: S & W N-frame Project

Postby mtngun » Sun Dec 10, 2017 1:50 pm

Expansion. Given enough velocity and given a big enough meplat to help initiate expansion, even hard bullets will expand.

The expansion that I see in the water tank is similar to bullets that I recover from game. Exception being lung shots that don't hit anything solid. A hard cast bullet typically does not expand at handgun velocities, but at lever action velocities the nose will "rivit" to become a full wadcutter, and is very effective.
Image

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Re: S & W N-frame Project

Postby mtngun » Sun Dec 10, 2017 5:41 pm

Today's target was very messy and the results were dissappointing so I'm only going to post the highlights and what it taught me. I'll break into a seperate post for each bullet.

I wanted to retest the coated 140 gr. gas check, but only had enough coated bullets for one group, so first I used uncoated bullets to settle on a powder charge:
-- 20.6 gr. WC297, uncoated 140 gr. GC, CCI 550, R-P cases. 6 in 6.1", 1656 fps, 72 ES. Moderate fireball.
-- 16.5 gr. 2400, uncoated 140 gr. GC, CCI500, R-P cases. 6 in 6.8", 1521 fps, 74 ES. Moderate fireball.

2400's velocity was 229 fps less than what Quickload predicted. The low velocity combined with the fireball taught me that 2400 was not happy pushing the light slippery bullet.

WC297's velocity was about 50 fps less than what Quickload predicted. WC297 was 19 fps faster than WW296 with the same charge, even though WC297 has a slower burning rate! :o This taught me that WC297 is a better behaved revolver powder than either WW296 or 2400. So I chose WC297 to retest the coated bullet.

-- 20.6 gr. WC297, coated 140 gr. GC, CCI 550, WW nickel cases. 6 in 5.5", 1715 fps, 83 ES. Moderate fireball.

The 5.5" group, 83 ES, and the fireballs taught me that the 140 gr. bullet is just too light to be a good choice for this application. A 140 grainer might work better with a jacketed bullet where the added engraving resistance would help the powder burn.

By the way, while all powders had a fireball and annoying blast with the 140 grain bullet, WW296 had the worst fireball, 2400 was next worst, and WC297 was least worst. Apparently WC297 really does have a flash suppressant. It does not eliminate flash completely but reduces flash compared to its cousin WW296. The more I learn about WC297, the more I like it.


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