S & W N-frame Project

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Re: S & W N-frame Project

Postby mtngun » Wed Nov 22, 2017 3:05 pm

Shroud and scope mount complete. It weighs 4 lb, 4 oz scoped but unloaded (the scope and rings seem to weigh 10 ounces).
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There may be a few details than need fine tuning:
-- I case-hardened the oversize bolt and put it back in, and now it's a little sticky, so I may need to take it out and stone it a tiny bit until it moves freely.
-- the barrel-to-cylinder gap is awful tight at 0.001" - 0.0015". My guess is that the gap may close up a bit after the new parts become acquainted with each other so I may need to shave a thousandths off, we'll see.
-- I tentatively plan to add a ball-spring detent to the crane so that it will become a "triple lock," but that can be done at any time.

Hopefully I'll be able to shoot it tomorrow and then I'll have a better idea whether it needs more tweaking.

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Re: S & W N-frame Project

Postby mtngun » Thu Nov 23, 2017 1:25 pm

I need to give this gun a name, what shall we call it? How 'bout M29-357? Then if I add more calibers later they'll be called M29-375, M29-40, etc..

Before shooting the M29-357 with magnum loads, I fired 6 lapping rounds, except instead of embedding the lapping compound in the bullet, I used a Q-tip to lightly smear lapping compound in the forcing cone before each shot. The idea was to lap the barrel, not the throats. The throats are already a perfect 0.358" so they did not need to be lapped.

Then I tried the M29-357 with several bullets that I had on hand. Today's goal was merely to check for basic functioning and to see if it had any clear likes or dislikes in bullets.
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There was a 10-15 mph wind that I did not attempt to compensate for, so not surprisingly all groups were dispersed horizontally. Also I was using a makeshift benchrest setup that was not very comfortable. No new records were set, but nothing terrible happened, either. Most of the groups had 3" - 4" vertical dispersion which I suspect is more representative of what groups would be like under better range conditions.

For what it is worth the best group of the day was shot with the Marlin load. Quickload thinks that load is 48 KSI though I seem to remember Pressure Tracing similar loads in the low 40's. At any rate it definitely exceeds the 35 KSI SAAMI spec so it is only suitable for strong guns. Its velocity is quite respectable for a wheelgun and should make a dandy hunting load.

This target was shot at 100 yards. My rule of thumb is that barrels 4" or less get tested at 50 yards while barrels 6" or more get tested at 100 yards, the idea being that you should test at the maximum range you would shoot in the field.
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All of the plain base loads leaded moderately in a stretch about 1.5" - 3.0" from the rear of the barrel, but there was no leading at the muzzle and no leading at the forcing cone. My Contender Carbine plain base loads also leaded about 2" from the breach and I always assumed that was related to the plain base melting and/or gas cutting shortly after peak pressure. Once the pressure drops below a certain point then the leading stops.

I have no explanation for why the plain base bullets lead in this gun but not in my Ruger Speed Six. This M29-357 is dimensionally correct and the bullets were sized 0.358" to fit the throats. But nonetheless for the time being I accept the gun's verdict that it does not like plain base bullets in magnum loads. From now on I will feed it either gas check bullets or coated bullets.

Photo was taken 2" from the rear of the barrel, where the leading was the worst.
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Everything worked OK on the gun other than the sticky oversize bolt and even that did not create any problems. Nothing rattled loose. At the end of the day I measured the barrel/cylinder gap and it was still 0.0015". So far the aluminum shroud seems to hold up OK to magnum loads.

Today's results suggest that the gun is capable of shooting 4" groups with it's preferred loads & good range conditions, however, I would like to shrink that to 2" groups. :lol:

Things To Try Next Time:
-- keep experimenting with different benchrest setups until I find something that is comfortable.
-- only GC or coated bullets. As time allows I'll create some new bullet designs for this M29-357.
-- it turns out that the Weaver's optimal eye relief was designed for someone with shorter arms than mine. I'll try moving the scope back an inch on the scope rail but it really needs to be 3" - 4" closer to my eyes. Word is that Leopold handgun scopes have more forgiving optics, but Leopold is awfully proud of their handgun scopes. :lol:

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Re: S & W N-frame Project

Postby mtngun » Fri Nov 24, 2017 6:50 pm

I used to wonder why everyone mounted their pistol scope so far back. Now that I have used a pistol scope for the first time in my life, that question has been answered -- because the eye relief was designed for a midget! From the point of view of weight balance I would prefer to mount the scope centered over the barrel, however, eye relief takes priority over weight balance, so I moved the scope as far back as practical.
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I rearranged the bench setup in search of something more comfortable. Because I am shooting through a narrow tunnel, I do not have the luxury of moving to a more comfortable spot. As it turned out, this setup was an improvement over last time, but still uncomfortable and still unsteady, so I'll have to continue trying different bench setups. :(
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Last time plain base bullets leaded the barrel, so today I tried coated plain base bullets. I debated whether to quench the coated bullets. When I experimented with coated PB rifle bullets, I found that they were very fussy about BHN, with a sweet spot between 11 and 14 BHN. Anything softer or anything harder hurt accuracy a lot. So I decided to go with the same BHN for today's revolver bullets, letting them air cool after baking. However, it's certainly possible that coated revolver bullets may play by different rules than coated rifle bullets.

Also I decided that for the time being I will try to adhere to the 35,000 psi SAAMI spec, that way anyone following this thread can feel comfortable with the loads that I post.

Rather than seat the bullets to their crimp groove, I seated to 1.610" COL, leaving 0.010" clearance in the 1.620" long cylinder. The M29-357 does not kick hard so a crimp is not absolutely necessary other than to aid ignition. A charge of WC297 was chosen that would hit 32 - 33 Ksi if you believe Quickload. Quickload predicted 1500 fps from an 8" barrel (it is my habit to omit the cylinder length in Quickload and that seems to compensate for the velocity lost due to the barrel-cylinder gap) and the chrono said 1500 - 1520, so that gave me a warm fuzzy feeling about the pressure estimate.
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Today's coated PB averaged 6.0" vs. 5.5" for yesterday's uncoated PB. While I did not shoot enough groups to "prove" anything, strictly speaking, there's no reason to believe that the coated bullets were more accurate, even though they did eliminate leading.

Nor is there any reason to believe that the PB Loverider bullet is more or less accurate than the PB TC design.

FYI the Loverider groups were shot with the scope at 8X, but I was struggling with the eye relief issue at 8X, so I switched to 6X to shoot the TC PB bullets. The eye relief was much more forgiving at 6X.

I felt like today's bench setup was slightly better than yesterday's, plus there was almost no wind today, nonetheless I still could not get comfortable. My uncomfortable bench technique is definitely adding at least 1 inch to the groups, maybe 2 inches.

-- Loverider load averaged 1512 fps
-- Loverider load averaged 69 fps six-shot ES
-- TC load average 1520 fps
-- TC load averaged 58 fps six-shot ES
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Things To Try Next Time and Down The Road:
-- retest the same loads except quenching the coated bullets.
-- keep trying different bench setups until I find something I have confidence in.
-- design bullets for this M29-357, with the crimp groove in the correct place, etc.. So far th M29-357 has not shown a strong preference for any particular design or weight, but there is much yet to try.

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Re: S & W N-frame Project

Postby mtngun » Sun Nov 26, 2017 2:55 pm

Today I retested the coated plain base except this time I quenched the bullets when they came out of the oven at 400F. I did not measure the BHN but past experience suggests they would be ~25 BHN.

Load deets:
-- J.R. brand reclaimed shot
-- Columbia Coatings Fire Plug Red hybrid
-- baked 400F for 23 minutes
-- quenched in water
-- BAC lube
-- final sized 0.358"
-- seated 1.610"
-- WSPM primer
-- 17.3 gr. WC297 for the TC and 17.0 gr. for the Loverider

When I began shooting the wind was only 10 mph but it was gusting to 30 mph by the end of the session, as verified by my Chinese wind meter. I haven't got around to measuring the BC for these bullets but if we assume the BC = 0.15, they would drift 4.5" in a 10 mph wind. If we assume the BC = 0.12 then they would drift 5.6". Ouch! :o In reality the point of impact was blown downwind an average of 3", but there was noticeable horizontal stringing.

The quenched Loverider averaged 6.3", no better than its air-cooled cousin.

The quenched TC bullet perked up and acted like it wanted to shoot, averaging 4.4". Two groups doesn't prove much especially when the wind is blowing so I want to retest the quenched TC under better range conditions.

Then I shot one group with 300MP just to check the burning rate. By that time the wind had increased to 30 mph and there was 6.9" horizontal dispersion but only about 2" vertical dispersion.

I had expected that the quenched bullets would shoot faster due to increased engraving resistance, but they actually shot about 10 fps slower. I have no explanation for the slower velocity. :roll:
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I had tweaked my benchrest setup yet again and for the first time I felt comfortable. It's not perfect yet but definitely a step in the right direction.

The best group of the day was shot with the scope set to 6X. All the other groups were shot at 7X. 7X is do-able but I do have to hold my head just right to keep the eye relief in the happy zone.
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Things To Try Next Time and Down The Road:
-- retest the quenched TC under calmer range conditions
-- possibly try seating the TC to its crimp groove rather than to 1.61" COL.
-- if the quenched TC continues to show promise then the next step will be to make a PB design better suited to this gun.

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Re: S & W N-frame Project

Postby mtngun » Mon Nov 27, 2017 1:47 pm

I tried switching to WW296, just to compare its burning rate to WC297. Otherwise the same load of 17.3 gr. powder behind the quenched & coated 160 gr. TCPB.

To my surprise, WW296 was about 90 fps faster than WC297 ! :o Up until now I had been using WW296, H110, and WC297 interchangeably, but now I know better.

Accuracy was poor despite calm range conditions. Shot at 100 yards, as usual.
Image

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Re: S & W N-frame Project

Postby mtngun » Wed Nov 29, 2017 6:07 pm

A bullet recovered from the berm, a coated 160 TC PB. I dunno whether it was air-cooled or quenched -- I suppose I could do a BHN test? UPDATE: 16 BHN so it was air cooled reclaimed shot. Normally it runs 12 - 14 BHN but can vary depending on cooling rate, plus I didn't bother to file off the coating before measuring and that may make a difference. Quenched will run around 25 BHN.

The good news is that it was engraved uniformly all the way around the bullet. By comparison, bullets recovered from my Ruger Speed Six are often engraved unevenly, perhaps due to misalignment of the cylinder with the barrel.

The bad news is that the grooves were nearly wiped out. Also, a ridge has formed around the base of the bullet that probably does not aid accuracy.
Image

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Re: S & W N-frame Project

Postby mtngun » Wed Nov 29, 2017 6:29 pm

A couple of new bullets to play with. First up, a 180 gr. GC. Up until now all bullets have had an 80% meplat, but starting with these bullets I'll standardize on a 75% meplat. An 80% meplat is sometimes marginally stable but 75% is usually reliable.

The bullet does not have a crimp groove per se but is crimped into one of the lube grooves. It's simpler to design it that way if you want to have a groove on the nose.

There is a single bore riding band. All the other bands are more or less full diameter. To ensure reliable chambering, the nose was sized in one of my rifle nose dies, just enough to size the nose to 0.357".

I can't think of any reason a gas check bullet needs to be coated but I wanted to try a few coated just to say that I tried it. :lol:
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And a bevel base version of the same basic 180 gr. design. Bevel bases seemed to have a slight advantage over flat bases in my TC Carbine experiments, but I don't know if that will hold true in a revolver. The theory is that the bevel will eliminate the finning that often occurs on a flat base.

This photo shows an unlubed bullet, but the loaded bullets were actually lubed with BAC.
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Shot at 7X under good range conditions. Today's accuracy was a step in the right direction though still short of my 2 MOA goal.

Now that I know that WC297 is not interchangeable with WW296, I had to go back to the drawing board on my Quickload calculations. I tweaked the WW296 powder data until it matched WC297 velocities, and used that to predict today's loads. I don't have 100% confidence in the tweaked data, but for what it is worth my tweaked data predicted 32ksi and 1460 fps with 16.0 gr. WC297, vs 1436 actual velocity today.

15.8 gr. seemed to give better velocity variation. QL thinks it generates 30 ksi.
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It was getting dark so that's as far as I got today.

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Re: S & W N-frame Project

Postby Bob » Wed Nov 29, 2017 6:53 pm

Impressive results and progress already Dan!

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Re: S & W N-frame Project

Postby mtngun » Thu Nov 30, 2017 9:10 am

Retesting the same 180 gr. GC that I tested yesterday, except today's bullets were not coated. They were oven treated at 470F and BHN should be ~35.

At the beginning the wind was blowing 5 - 10 mph, picking up to 10 - 12 mph toward the end so I decided to call it a day, bearing in mind that a 10 mph wind makes these stubby pistol bullets drift 5 inches at 100 yards.

At any rate, there was not much difference in accuracy, with today's uncoated bullets averaging 3.48" vs. 3.35" for yesterday's coated. Two groups is not enough to "prove" anything, anyway, so for now I'll call it a toss up in the accuracy department.

However, the uncoated bullets averaged 70 ES and 1.82% standard deviation, vs. 39 ES and 0.95% SD for coated, and that may be significant, though more data would be needed to be sure.

6 shots at 100 yards.
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To coat or not coat, that is the question? It doesn't seem to make a big difference, but if the accuracy is equal then I'd favor the coated if they have a lower ES.

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Re: S & W N-frame Project

Postby mtngun » Sat Dec 02, 2017 9:45 am

A couple of new bullets to try out. They're all the same basic design, and at the moment all my GC bullets are coated and quenched.

They each have one single bore riding band, as called out on the photo. I'm not at all sure if that is an optimal design, at this point it's just a guess.

Because I wanted to avoid a long front band that would distort the bullet when engraved, I used a loverin-style bullet with lots of grooves and crimped in one of the grooves. However, that hasn't worked out so well -- it's hard to put the grooves in exactly the right place for a crimp, and the grooves are too narrow for a heavy crimp.
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The 140 grainer did not shoot well, and I gave up after only the one group. I never expected the short, stubby bullet to be accurate at 1700 fps, but it was interesting to try. Perhaps it would be more accurate if I reduced the velocity but I'm testing all loads at ~33ksi to try to make the comparisons apples-to-apples.

The majority of today's targets seemed to have a diagonal pattern, highlighted by the green line
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Later I recovered a coated GC bullet from the berm. The nose was too damaged to tell which bullet it was, but it might have been the 140 grainer. It worries me that the grooves have nearly collapsed.
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My tweaked Quickload data for WC297 has been doing a good job at predicting velocities. However, extraction was a little sticky with the 200 grainer's 14.0 gr. charge even though Quickload predicted only 32 Ksi. Perhaps Quickload is wrong about the pressure, or perhaps this cylinder simply sticks at modest pressures. At any rate, accuracy was mixed with the 200 grainer.

In case you are wondering, I photoshopped the target photos so that you see only one bullet's targets at a time. This 200 grain target only shows the 200 grain bullet holes, the 140 gr. target only shows the 140 grain bullet holes, etc.. The different groups actually overlapped and made for a messy target that would have been hard for you to understand if didn't clean it up with photoshopping.
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Previous tests with the 180 GC had yielded 3.5" without really trying hard, so this time I tried hard and hoped for even better accuracy, only to get disappointing accuracy and also disappointing velocity variation. I tried tweaking the charge, the seating depth, and the crimp, but it didn't seem to make much difference. What the hell happened to this bullet's 3.5" groups? What happened to its 39 - 49 ES? :x
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Last time the coated 180 BB had shot a 3.9" group, but I could not repeat that today. :cry: Minor tweaks to the powder charge and seating depth didn't seem to make much difference.
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I wondered if accuracy with the 160 gr. coated PB would improve if I seated them deeper and crimped them firmly? Nope. Velocity variation did not improve, either.

This was the 160 gr. Loverider that I had tested before, and averaged 5" - 6". Today it still shot 5" - 6", so at least it's consistent. :lol: :lol: :lol:
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This has been a long post so I'll sum things up in the next post.


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