SC 340 Marks on Cylinder and Frame

Fritz007 · Dec 20, 2009

Hello,

have these strange corresponding marks on cylinder and frame. On the cylinder they are fife times. Looks as if cylinder gets into contact with frame on shooting. Inspecting the gun I can't verify this. Cylinder is clear of frame, no excessive play to be seen. Looks as if Cylinder can't get into touch with frame at this position.

Thanks for your help.
Fritz

500 Magnum Nut · Dec 20, 2009

Only thing I can think of is something got stuck there and scratched it. Maybe somebody tried to bend the yoke around and stuck a wedge in it at that point.
The gun can't make that mark by it's self.

s&wchad · Dec 20, 2009

If you have that same mark in five locations on the cylinder (near the stop notches), something's seriously wrong. I'd phone S&W and have them send a shipping label, so they can check out the gun (no charge to you). I wouldn't shoot it as is.

How about posting a photo of the recoil shield and the back of the cylinder. Maybe check the frame under the barrel for a crack.

perpster · Dec 20, 2009

Beats me. Is it just on the surface, or does it dig into the metal?

HEADKNOCKER · Dec 20, 2009

The cylinder shouldn't touch the frame there..
I too would be thinking the yolk, which is aluminum alloy BTW on the Airlites, may be misaligned or bent slightly..
I would be calling S&W for the shipping label..
If you carry this piece for Self Protection nothing is too good for it..
Let us know if the cylinder touches on each cylinder bolt stop & any other things that look amis..
Keep us informed of what S&W does for you on this matter..
GOOD LUCK!
Gary/Hk

Fritz007 · Dec 21, 2009

Some more pictures

Here are some more pictures:

Frame and cylinder are clear from each other. But when I force the cylinder down with my fingers, I nearly - but not totaly - can close the gap. I can imagine that the force of a 357 load will be able to force this completely down.

Thanks for your input,
Fritz

Fritz007 · Dec 21, 2009

One more picture

Fritz

Fritz007 · Dec 21, 2009

Did look at the gun again. For ease of understanding I reference the explode at
SW36

Between the Locking Bolt (5147) and the Center Pin (7062) there is quite a bit of play say 90% of what is needed to unlock the cylinder. The Center Pin Spring (5227) is not very strong. I easily can imagine that under the heavy recoil of a 357 magnum load in this 12oz gun the Center Pin (7062) moves forward against the somewhat weak Center Pin Spring (5227), gaining momentum and pushing the Locking Bolt (5147) that little bit that is lacking to unlock the cylinder forward.

If I push the Center Pin (7062) forward using the Thumbpiece (5613) I easily can get the cylinder in touch with the frame.

Guess that is the catch. Can anyone owning a Scandium Snubby confirm that this is NOT the case with his gun.

BTW, as the tip of the Center Pin (7062) facing the Locking Bolt (5147) looks "worked" on my gun, can anyone tell me how deep the Center Pin (7062) is in the Extractor Rod (5255)? Maybe that someone messed around with that piece because the cylinder was somewhat difficult to close. I am wild guessing ;-)

Thanks,
Fritz

Fritz007 · Dec 21, 2009

Lock Bolt and Center Pin

The more and more I think about it, I come to the believe that it is the Center Pin and Lock Bolt which are the culprits.

On maximal protrusion the Center Pin barely touches the Lock Bolt. You nearly can't tell that the both parts are touching each other on unlocking and locking the cylinder. Eyballed about 3 thousands overlapping of the two parts.

The Center Pin recesses into the Extractor Guide about 6 to 7 hundreds of an inch. Center Pin looks as if it has been filed down and shows big marks.

Just to be complete a photo of the Lock Bolt:

Another wild guess:
The initialy rough MIM parts of the Thumb Piece and the opening mechanism lead a customer to return the gun for repair. The gunsmith tried to fix the problem in taking some resistance on the closing by simply filing down the Center Pin. Did not work, customer returned the gun, was refunded and the gunsmith looked for another customer. That is the moment when I enter the picture ;-)

What do you think about that? Can anybody owning a J-Frame compare his gun to mine?

Thanks,
Fritz

tomcatt51 · Dec 21, 2009

The locking bolt should engage the extractor rod. It should be in contact with the center pin. Clearance between the center pin and the locking bolt gives the center pin a "run" at the locking bolt under recoil. When you push the cyl release (and bolt) forward to release the cylinder the bolt should be flush with the face of the recoil shield and the center pin should be flush (or extend minimally beyond) the end of the extractor rod.

Is the locking bolt (in the barrel underlug) butchered or stuck so it doesn't extend properly and engage the extractor rod? The spring preload on the locking bolt helps the center pin stay put under recoil (along with the center pin spring). Has the end of the center pin been shortened (butchered) on the end that engages the recoil shield? Has the center pin spring been clipped/shortened?

Fritz007 · Dec 21, 2009

Butchered is the right wording

tomcatt51 said:
The locking bolt should engage the extractor rod. It should be in contact with the center pin. Clearance between the center pin and the locking bolt gives the center pin a "run" at the locking bolt under recoil. When you push the cyl release (and bolt) forward to release the cylinder the bolt should be flush with the face of the recoil shield and the center pin should be flush (or extend minimally beyond) the end of the extractor rod.

Is the locking bolt (in the barrel underlug) butchered or stuck so it doesn't extend properly and engage the extractor rod? The spring preload on the locking bolt helps the center pin stay put under recoil (along with the center pin spring). Has the end of the center pin been shortened (butchered) on the end that engages the recoil shield? Has the center pin spring been clipped/shortened?

The locking bolt does virtually not engage in the extractor rod. It only goes about 3 thousands into the extractor rod. You can get an idea of this if you look at my post from 8:13am. Not sure, but the locking bolt has working marks on it. Might be "butchered". It is not stuck anyway, it moves freely, but is in any case to short to engage into the extractor rod.

The center pin looks as if it has been "butchered" at the end facing the locking bolt.

At the site facing the recoil shield, the center pin has a "factory" look, i.e. no marks of filing or so.

The bolt that is manipulated with the thumb piece is flush with the surface of the recoil shield when I put the thumb piece fully forward. This looks good.

tomcatt51 it looks as if you are right. The center pin has about 6 to 7 hundreds room to run and gain momentum to push the locking bolt about 3 thousands. Then the cylinder is unlocked at both ends.

Trying to understand what is going on,
Fritz

Fritz007 · Dec 21, 2009

Just another oddity. Cylinder gap is about 2 thousands. Somewhat tight, isnt it? And the barrel facing the cylinder is not realy square. 2 thousands of cylinder gap on one side, 4 thousands on the other side.

The locking bolt definitely does not engage in the extractor rod more than 3 thousands. As the locking bolt is kind of a cone, the cylinder is not led by the locking bolt. Guess the locking bolt has been shortened to ease the operation of closing the cylinder.

A puzzeled Fritz

tomcatt51 · Dec 21, 2009

The uneven B/C gap is pretty common, if you look at the barrel face you can see the marks from the gap being "adjusted" with a file. You check B/C gap with the cylinder held to the rear, maximizing the gap.

Sounds like the locking bolt needs replaced for starters and maybe the center pin if it doesn't come up at least flush with the extractor rod. You're trying to keep the center pin from disengaging the recoil shield during recoil, which obviously is a bunch with a gun that light shooting .357 mags.

Fritz007 · Dec 22, 2009

What about the stress the yoke and its bearing in the frame, hence the whole frame, has undergone during unlocked shooting? After all the yoke has been bent quite a bit and alloy isnt famous for benting. Usually it is said to crack before benting.

Should (and can) I on returning the gun insist on replaement of the stressed parts?

Fritz

Fritz007 · Dec 22, 2009

Did send the gun back. Stay tuned, I will keep you informed about the repair.

Beforehand another question. The surface of the cylinder and the frame are "spoiled". The visual effects of the destroyed finish don't bother me at all. But are there any negativ effects to be feared, kind of starting point for oxidation or the like?

Is it necessary to replace the "bent" parts, i.e. crane and frame?

What should I require them to do?

Thanks for your opinions!
Fritz

tomcatt51 · Dec 22, 2009

Fritz007 said:
Is it necessary to replace the "bent" parts, i.e. crane and frame?

Flexing and bending are two different things. It the yoke was "bent" there would be permanent mis-alignment vs "flex" which allows the cylinder to move (contact the frame) but return to it's original position.

Fritz007 · Dec 23, 2009

Apparently the phenomenon is not completely new. See the post of user johnbffb in the thread linked below:
S&W 329PD cylinder lockup - Shooters Forum

Fritz, a man depreviated of his wheelgun

Fritz007 · Jan 1, 2010

Found another one. Sold as new "exhibition gun", exposing the marks. Is there anybody out there, owning a scandium wheel gun with the marks? Would be interesting to learn about this.

How often the inertia of center pin and locking bolt overcome their corresponding springs force to unlock the cylinder when you shoot magnum loads from a scandium gun?

Fritz

perpster · Jan 2, 2010

Fritz007 said:
Found another one. Sold as new "exhibition gun", exposing the marks. Is there anybody out there, owning a scandium wheel gun with the marks? Would be interesting to learn about this.

How often the inertia of center pin and locking bolt overcome their corresponding springs force to unlock the cylinder when you shoot magnum loads from a scandium gun?

Fritz

Fritz,

My 340Sc has a mark adjacent to and just to the front of the cylinder stop. It is like a triangle pointing to the front of the frame. The base of the triangle is just slightly narrower than the cylinder stop opening's width. The length of the triangle is slightly less than the length of the cylinder stop opening's length. Basically, it looks like a little Christmas tree shape with it's wide portion adjacent to the opening.

There is also a square mark behind the opening, between the opening and the bottom of the recoil shield.

Now, 2 years ago I had a problem when cylinder wouldn't open on 2 chambers. I sent it to S&W and they "repaired the extractor rod". IIRC they said it was slightly bent. I don't know if the marks were there before or after this problem or were caused by it.

I wonder if it is possible that the alloy frame and titanium cylinder momentarily flex and contact each other during firing, especially if everything is not aligned correctly.

BTW, when the cylinder is closed and I push on the thumbpiece, the locking bolt protrudes out the front approx. 1/8" (just a guess on the measurement). When at rest it is just a slight bump sticking out.

The finish wear on the front of the cylinder is normal and AFAIK not a problem.

Good Luck.

Fritz007 · Jan 2, 2010

perpster said:
Fritz,
... when the cylinder is closed and I push on the thumbpiece, the locking bolt protrudes out the front approx. 1/8" (just a guess on the measurement). When at rest it is just a slight bump sticking out.

perpster, thank you for your input. Are the locking bolt and the center pin in contact when the cylinder is closed? If there is a gap, how wide is it (eyeballed)?

My guess is that if you (me) don't fix the problem with the cylinder locking as indicated by these marks which I described in my initial posting you will end up with a bent cylinder axis or a ruined frame. If you don't get a serious problem caused by a bullet not properly entering the forcing cone...

Thanks again,
Fritz

SC 340 Marks on Cylinder and Frame

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