Principle of "The Double Lockup"


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Mike-SoCal
July 23, 2003, 12:22 AM
I have read where my large frame Dan Wesson and the Rugers have a double lock-up at the cylinder. Can someone provide a definition of what this feature entails and why it seems to be a desired characteristic for revolvers designed to shoot heavier cartridges. Thanks.

Mike

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Jim March
July 23, 2003, 03:29 AM
On a classic DA Colt like the Python, the cylinder latches into the frame at the rear of the cylinder only. Out at the crane, it can "wiggle back and forth", so the alignment of the back of the barrel to the cylinder bore is a bit iffy under recoil. Only the crane's stiffness holds that end straight, but that's at the end of a couple inches of metal bar (the crane).

To make up the difference, Colt heat-treated the crane better. On their best guns of that type, such as the Python, it wasn't too much of an issue. On "lesser stuff" like the Dick Special, Police Positive or similar, it was a bit more troublesome as a long-term thing.

On your average S&W, there's still no lockup "right at the crane". The very tip of the ejector rod is dished and "plugs into" a spring-loaded button under the barrel, so that end of the ejector rod is "loosely locked". But as the ejector rod is skinny and can wiggle, the increased "cylinder stiffness under fire" over a Colt is marginal.

Like the Colt, the S&W locks at the rear.

Ruger and then DW and Charter Arms came up with a latch that locks the crane solidly into the frame, in addition to the latch at the rear. With the cylinder "axle" held stiffly at each end in the frame, both accuracy and reliably are at least theoretically improved.

S&W played with a crane lock briefly, while retaining the "semi lock" at the end of the ejector rod. That was known as the "triple lock". Ruger, DW and Charter all realized that the latch at the end of the ejector rod was of limited usefulness, so they either let the ejector rod free-float (early Charter) or enclosed it in a shroud but otherwise didn't retain it (late Charter, Ruger DAs, Dan Wessons.

Ruger, DW and Charter all rigged up "interlinks" allowing release of both locks (each end of the cylinder) with one button. On Rugers, the release switch is at the rear, DW mounts theirs on the cranes, early Charters had TWO releases (crane and S&W-style button) that were linked to each other. The forward "switch" (actually pulling the ejector rod forward) was deleted on later versions but it's still locking up at both ends.

When Taurus played with two locks on their "Raging" series, they were too stupid to rig up an interlink so they ran two switches, one for each lock. It's got both a DW style crane-switch and an S&W style switch. You have to manipulate both switches at once to swing the cylinder out; OK on a hunting gun but sucky on a defensive piece :rolleyes:. (This may actually be marketing; if people are activating both switches, they'll KNOW there's two locks, and think it's an advantage over, say, a Ruger SRH 454. Wrong. The Ruger has two locks too, but their engineers weren't smokin' something funky when they did their thing.)

On any DA Ruger, swing the cylinder out and push on the back of the cylinder axle pin from the rear while looking at the crane. You'll see a little switch move back and forth at the crane, which fits into a cutout in the frame to match. That's the forward latchwork and you're also seeing how the interlink works.

On a Charter, the ejector pin is "oversize" and backs into a cutout hole in the crane, freezing crane motion during firing.

I haven't examined the DW lockwork but I know it's functionally equivelent to the Ruger except for the funky switch position.

Jim Watson
July 23, 2003, 10:03 AM
"I haven't examined the DW lockwork but I know it's functionally equivelent to the Ruger except for the funky switch position.

Jim March"

The Dan Wesson LOCKS only at the crane. The rear engagement is just a ball detent in the breechface that clicks into a dimple in the center of the star. At least that was the system in the first generation DWs I played with some in the '70s. Have they changed lately?

Jim March
July 23, 2003, 12:31 PM
Hmmmmm. Interesting. Jim, is it possible there's a difference in the lockwork between the large and small frames? Because I can't imagine a ball-detent lock would work well on, for example, the 445Supermag or other hot-rodded Dan Wesson calibers. Hell, I wouldn't trust that in 44Mag.

I remember reading somewhere that a DW locks at both ends but now that I think about it, I *think* that a reference to the larger frame.

Mike, so you understand, a "ball detent lock" is where there's a springloaded ball bearing that drops into a matching dimple. It's not a "true lock" but it can help. Some gunsmiths add such a thing to S&Ws at the crane/frame junction, giving K-frame/L-frame/N-frame S&Ws a "partial lockup at the crane".

Some makers call such a "lock" a "lock", ever since S&W came out with the "triple lock" and one of the locks (at the end of the ejector rod) was a form of such a bearing detent lock.

Standing Wolf
July 23, 2003, 09:53 PM
...there's a springloaded ball bearing that drops into a matching dimple. It's not a "true lock" but it can help. Some gunsmiths add such a thing to S&Ws at the crane/frame junction, giving K-frame/L-frame/N-frame S&Ws a "partial lockup at the crane".

The good folks at Clark added one to my Smith & Wesson model 27 when they replaced the barrel. It works just fine, and gives the gun a stronger, more reliable front lock than the spring-loaded gadget the ejector rod clicked into. If it need be said, the Clark barrel is much more accurate than the factory's.

http://www.clarkcustomguns.com

Jim March
July 23, 2003, 10:51 PM
Standing Wolf: yes, a ball-detent add-on "lock" at the crane can indeed help a lot. Does more good there than it does at the end of the ejector rod, that's for damnsure.

I suspect that a true LOCK versus detent at the crane is better, but I confess to not being dead certain about that, at least in all cases. The S&W N-Frame is already pretty strong, so adding that last extra bit might be just what the doctor ordered.

I would bet that a 27 that's been seriously stepped on by Clark's in the fashion you described can shoot :). Probably at Python/Freedom Arms levels.

ChristopherG
July 24, 2003, 07:01 AM
Yipee!, I thought to myself, when I saw a long, discursive reply by Jim March at the top. Thanks for all your information-dense and lucid writing, Jim.
CG

Standing Wolf
July 24, 2003, 08:36 PM
I would bet that a 27 that's been seriously stepped on by Clark's in the fashion you described can shoot. Probably at Python/Freedom Arms levels.

Yep. The rate of twist in the rifling is faster than in a Python's barrel, so it stabilizes light loads very well. The original 8.375-inch barrel was a lousy shooter from start to finish. Twenty-odd years after I consigned the gun to the closet, I sent it to Clark. Sad to say, the bull barrel was too heavy for what's left of my wrist. I had a six-inch model 28 barrel put on it, which shot well, but looked funky. Finally, I mentioned it to my local gunsmith, who cut down the Clark barrel and removed a considerable amount of metal. The trigger isn't as good as a Python's, but the barrel is a joy and delight. One of these days, I'll take some pictures.

Mike-SoCal
July 25, 2003, 12:53 AM
Thanks, one and all for the comments and on going discussion.

Jim, I appreciate you providing a definition of "ball detent lock." ; For better or worse, my two year old Dan Wesson large frame .460 and .357 SuperMag has that as part of it's locking system.

Mike

Jim March
July 25, 2003, 02:14 AM
That is really weird about the DW. It's gotta have one HELL of a strong spring under that ball bearing!

It seems to me that it's the crane that needs to be locked up the tightest. Not 100% sure about that, but it seems reasonable. Apparantly, DW figures that if the crane lockup is REALLY good, the lockup at the rear of the cylinder can be mediocre and the whole thing still works.

Hmmmmmponderponderponder.

You know, with no "interlink" needed between the front and rear locks, the cylinder pin ("axle") can be solid. Maybe that helps stiffness too? With the Ruger DA system, the cylinder pin is hollow and the interlink connection runs through it.

Weird. I'm not willing to call DWs "junk" over this.

Standing Wolf
July 26, 2003, 11:03 AM
Here's a painting of the model 27 mentioned above.

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