Cylinder stop height adjustment for full notch engagement?
I also posted this over on the blue forum, but I figured I'd ask here as well, since we're likely to have some formerly trained armorers and qualified smiths around here.
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Read the FAQs, did a search, didn't find what I was looking for. I'm going through an M&P 340 and cleaning it up, deburring, etc. For example, I just finished addressing the three long ratchets the factory gave it. Bonus metal...
Anyway, the M&P has a Centennial frame, so it will only be fired and dry fired DA. One goal is to minimize cylinder notch peening. I measured the protrusion of the cylinder stop from the frame, the depth of the slots in the cylinder, and the clearance from the cylinder to the frame. It looks like I have ~0.010 of cylinder notch depth that isn't engaged by the cylinder stop. The gun does time and lock up correctly, no rotation in either direction. I'm just talking about maximizing engagement to optimize durability.
There's plenty of trigger pre-travel before it picks up the stop, so I could adjust the stop to sit upward ~0.008 or so in the frame. Still wouldn't be bottoming the stop in the notches, but would have a little more engagement of the stop against the side of the notch, increasing the contact area when the cylinder stops rotating, thereby reducing the stress on the side of the cylinder notch and theoretically reducing any tendency for peening to develop. To put numbers on it, I would increase the engagement of the stop in the notches from ~0.037 to 0.045, slightly more than a 20% increase, but due to the shape of the stop, the increase in contact area would be even more. Seems worthwhile if there are no negatives associated with it.
It does make sense to pay attention to the engagement of the stop in the frame window, and make sure that the raised position doesn't give up any bearing surface of the stop against the frame. The aluminum frame, even though scandium alloy, can be expected to peen or wear more/faster than the steel cylinder, so one obvious limit to how far the stop should be raised is giving up any engagement with the frame.
p. 69 of Kuhnhausen says:
Quote:
...the next step is to check for and adjust the cylinder stop to full vertical cylinder stop/cylinder locking slot engagement plus an extra .005" and then check for possible cylinder roll/backroll disconnect.
I'm a little uncertain what is meant by this. Is it make the cylinder stop "bottom" (upward) into the notch, then an extra .005" so that when the cylinder is swung out, the stop is .005" higher than the deepest point of the notch? (That seems logical to me.) Or is it make sure you just have "full" engagement, defined as enough to lock the cylinder in each direction, and then another .005"? I would think if the former, that would take care of any possible cylinder roll/backroll disconnect. Maybe I'm just reading too much into that.
The only problem I can think of is the trigger failing to pick up the stop if the stop was too high, but that's pretty easy to leave plenty of reserve, going a little at a time. And as I said, there is currently significant pre-travel, so lots of room there. Raising the starting point of the stop will cause the trigger to pick it up and begin moving it sooner, but once it passes the original position, all the timing relationships that follow will be unchanged.
Is this a thing that is regarded as worth doing? Is there any problem I haven't figured out that would result if I raise the stop?
(Also, I'm not going to type an essay about it, but given what I've just been through fixing on this gun - and a bunch of other S&Ws I've worked on - the notion that S&W built it right in the first place and I should leave it alone just doesn't hold water. S&W didn't build it right in the first place (or even the second time they had it), and if left alone, it would have chewed itself apart in short order. I've written many times that a new S&W is an almost-ready-to-fire revolver kit that ships fully assembled only because that's the easiest way to QC that all the parts are included, and I stand by that.)
