[Nightcrawler]

A S&W 6-shot L-frame in .40. Can't remember the model number. Six-something-six, I think. 4" barrel. Like all 4" L-frames, it was good looking. I didn't know they made a .40. $509.00.

However, I'd probably be more into the N-Framed 610, myself. Or the 625.

[Brian Williams]

It is a 646 and would be a hot seller if it did not have the titanium cylinder.

[Nightcrawler]

What's wrong with the titanium cylinder?

So, anybody have one of these? I guess it's as close as you're going to get to a 6-shot, big-bore L-frame, isn't it?

[Clemson]

I have seen and played with one of these 646's also. I like the feel and heft of the gun. As I understand it, the Titanium cylinder is what makes it possible for S&W to make a .40 caliber on an L-frame. The 610 is an N-frame, with thicker cylinder walls. The Titanium cylinder is supposedly much stronger than a stainless steel cylinder.

[SnWnMe]

Okay, I don't get it. Smith can shoehorn an extra charge hole in a 686+ thereby giving it less metal between chambers, yet the gun holds @ 357 pressures. But 6 charge holes for 40S&W operating @ 9mm pressure (180gr 950~980 fps) cannot be done?

Maybe I am oversimplifying this:

Pi x Dia x # of charge holes = total area of cylinder face required?

3.1416x.356x7=7.83sqin for 357

3.1416x.4x6=7.54sqin for 40

So, within the confines of an L frame cylinder, a 7th hole in 357 will result in less material between chambers than a 6 shot 40.

Perhaps it's a metallurgy thing that dictates a ti cylinder?

[Clemson]

It isn't a function of area. It is a function of wall thickness. The centerline of the chamber hole must be the centerline of the bore. A .40 caliber case will have about 0.022 inches less wall thickness than a .357. {.400 - .357}/2

[farscott]

I believe the seven-shot 686 is possible because the bolt stop notches are between the charge holes, not directly adjacent to the charge holes like the six-shot revolvers. The minimum cylinder wall thickness is a function of the diameter of the cylinder, the location of the charge holes, their diameter, and the depth of the bolt stop notches in the six-shot revolvers. In the seven shot version, the depth of the bolt stop notches are immaterial to the minimum wall thickness of the cylinder due to their location.

While I am not sure if the pressures of the .40 S&W round and the L-frame cylinder dimensions of the M646 dictated a titanium cylinder, I assume S&W had some reason, real or perceived, for using the material in the cylinder. The reason may not be directly related to the M646; perhaps the original M646 design choices were used to test a design concept. Since the original M646 was a PC revolver, it may have been a way to test the perfomance and marketability of some concept. Since the new M646's are made from parts from the original run, I assume the experiment was not a success.