what is the purpose of a locking bolt pin ?

armorer951 said:

Not a dumb question. Based on the wording in your question, I'm assuming you are referring to the front locking bolt.

The front locking bolt in the Smith and Wesson revolvers, which is basically a spring loaded detent, was designed to help stabilize and support the extractor rod, and add support to the front portion of the yoke during the stresses of firing. Due to it's design, the front locking bolt is only marginally effective in assisting in stabilizing this area at the forward end of the extractor rod.




Technically, in terms of nomenclature, the locking bolt "pin", as you described it above, serves only to hold the spring loaded front locking bolt in place inside it's cavity in the barrel.

The center pin itself is spring loaded inside the extr. rod, but is not attached to the rod, and moves forward and back inside the cavity in the extractor and the attached extractor rod completely independent of these other parts that make up the assembly. Spring tension on the center pin is provided by it's own coil spring.

If the extractor rod unscrews and "backs out", this has no effect on the center pin's position in the breechface. If the extractor rod continues to unscrew, this eventually prohibits the free rotation of the cylinder, locks the end of the extractor rod over the tapered end of the front locking bolt, and prevents the user from opening the cylinder using the thumbpiece. (which, when pushed forward, pushes the center pin forward to release the locking bolt)

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murphydog said:

This is an opinion and is worth exactly what you make of it.

The very first S & W Hand Ejectors (.22 HE or Ladysmith, model 1896 in .32 Long, and the model 1899 in .38 Long Colt/Special) did not have the forward locking point for the extractor rod.

Adding this feature onto later guns may have been a marketing point against Colt, but every S & W revolver since then has had either the front and rear locking points (the vast majority of HEs), the rear with a ball detent yoke lock (the newer model 19s, 66s, and the 460 and 500), or three locks (no fair guessing which model ).

So, you may wish to ask your gunsmith if he thinks a second lock of some form is not necessary because he thinks the gun will never shoot loose, even with heavy .357 use, or because he does not install them regularly.

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steelslaver said:

I can also develop end shake where the cylinder moves forward and aft. and the parts you are talking about are know as the cylinder stop and stop notches. If you will observe the hand or small pawl which comes through the recoil shield portion of the frame and engages the teeth on the ratchet rotates the cylinder on a S&W counter clockwise and against the yoke that holds the front of the cylinder in position to the barrel. This can cause to yoke and of course the cylinder to move very slightly away from the frame and alignment. The lug under the barrel was designed to minimize this. Totally necessary? No. A good idea? Yes. Although slightly difficult to install on a custom barrel, a ball detent setup in the yoke is really easy. I think it is more a case of don't want to bother with it that anything else. The number of revolver smiths in the UK has got to be pretty small these days.

Colt has never used them. True. But, then Colt has its hand on the other side of cylinder and rotates its cylinder so that it presses crane into the frame.

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armorer951 said:

It's actually called the "locking bolt". It resides in the barrel, is held in place by a cross pin, and powered by a small coil spring. Fitting them is a chore. They are rarely fit correctly.

Most of the time they are fit to extend too much, which causes the locking bolt to bear too heavily against the cavity in the extractor rod. Occasionally they are too short, and do not accomplish the task they were designed for, which is to support the end of the rod, without impending on the cylinder's rotation.

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armorer951 said:

Without the locking bolt option, I've always installed a ball detent in the yoke, which locks into a small cavity placed above it in the frame. This supports the yoke, and holds the cylinder firmly in alignment with the chambers of the cylinder, assuming that the timing is correct and parts have been correctly fit.

I never did any testing to confirm that accuracy and consistency were improved by this add on, but I personally believe that to be the case. Purely an opinion though.

Here's a photo of a ball detent I installed in the yoke of one of the many PPC revolvers I built back in the '70's and 80's....... when dinosaurs roamed the earth.

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steelslaver said:

You can get a kit for the ball and it is inexpensive. Basically some small ball bearings, springs and a special cupped bunch. Drill the correct sized hole to the depth in instructions, insert spring with ball on top, press punch on top of ball till punch touches yoke and give punch a firm tap with hammer. You must use a drill vise and drill press to drill the hole. It must be perfectly vertical and centered so it doesn't go outside of yoke or hit hole for ejector rod. Once yoke has ball, install it in fram without cylinder, put some layout dye on top of yoke cut and open and close yoke a few times. This places a line in layout dye where ball rides. Udsing a small ball carbide cutter in a Dremel type tool make a small round pocket at far back on the very end of that line, checking to see when ball enters and holds the yoke in place. Takes maybe a hour total with no rush.

Here is a link to kits. The fixture has a setup for positive location of hole.
POWER CUSTOM CRANE BALL DRILLING FIXTURE for S&W | Brownells

Should be able to ship anywhere as it is just springs and balls and a punch

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