I recently bought a new model 640 Pro. I can see that the front sight is slightly canted to the left. I am wondering if when manufacturing the handgun, is the barrel to frame aligned by "eye", or is it done automatically by machine? If the latter, could an entire run be misaligned if the machine were not adjusted perfectly?
I intend to send the gun back to S&W for adjustment. In my experience canted front sights were much more common on single action Colts.

I can't answer your question cancerning the specifics of how the barrels are fitted to the frame. One of the videos (youtube) showing the operation and building of revolvers in the Performance Center shows an assembler fitting a barrel by hand. After placing the barrel in a vise, he used what appeared to be a large aluminum wrench of sorts. Kind of scary.

In this day and age, and with the development of lasers and machines that run off computers, I would think they would be able to index barrels with precision. The truth is, there are still many issues with canted barrels these days. I just bought one last year afflicted with this awful malaise. Apparently, some degree of "cant" is acceptable. Perhaps barrel cant should be spelled "can't"......I sent it back, they returned it still "can'ted".....and pronounced it fixed. The gun still shoots 2 inches left at 7 yards.

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Ret. LE, FA Instr, S&W Armorer

They are assembled by hand and having taken time to correct this issue on my 625 I can state from experience that lining the barrel up isn't nearly as simple as many assume.

First there is the amount of torque used to tighten the barrel, I would estimate it's around 50 ft.lbs. Note, having assembled MANY Chevy Small Blocks when I was a pretty serious gearhead I can assure you that estimate is pretty close.

Second, the barrel has to be "captured" in a vice block that will hold it securely and not mark it up. So there really isn't much of the barrel visible to line up with the frame. In my case the Delrin vice block I made only left about 1/4 inch visible at the rear where it met the frame.

Third, the frame wrench I was using is fitted to the frame in the area of the cutout for the yoke, so there is only about 1/8 inch of the frame showing where in meets the barrel.

Finally, that frame wrench has a "handle" that is only about 12 inches long. Ever try to hit 50 ft.lbs. with a wrench that is that short? You have to be a real gorilla to get there and have control. I used a 20 inch of pipe as a cheater and the end result is that I'm darned near arms length from the area I need to see clearly to get that joint to line up.

Now for the end result of that work. The barrel is lined up dead nuts perfectly. AND my 625 shoots slightly left. Turns out that I should have over rotated the barrel slightly if I wanted it to shoot dead on with the rear sight perfectly centered. However I'm not going to do anything about that, once was enough.

BTW, before I started the barrel was over rotated enough I had to run the rear sight full left to get it zeroed with my preferred range load. With my preferred SD load it shot too far right to correct for. I also decided to do this myself because i wanted to lap the forcing cone at the same time to see if that did anything for improving accuracy. Truth is I cant shoot well enough with iron sights to know whether lapping the forcing cone did anything.

They are all done by hand by this guy:

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So many S&W's, so few funds!!

I can see that it would be very difficult to make fine adjustments in that manner. However, on the 640 Pro, both front and rear sights are dovetailed, so sighting in is possible and preferable with both sights vertically aligned.

The last operation is a guy with a padded vise and wrench and eyeballs the rotation of the barrel. I hear that plus/minus 5 degrees is 'in spec', which I think is ridiculous in this day and age. A minute index mark under the barrel and on the frame would be ideal.

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"He was kinda funny lookin'"

AFAIK, the barrels are still torqued down by hand....... hence the awful and inconsistent alignments on recent years.

Which is why the barrel and frame underneath should have alignment marks. It would also be VERY EASY to use a bore laser to check bore alignment to sights (I own one) and it is very accurate. Shipping guns with canted sights just reflects a "don't care" QA attitude that it inexcusable because it is so easy to remedy.

Smith & Wesson has been manufacturing revolvers for over 150 years, if they can't get the sights aligned correctly maybe they should just close up shop and admit defeat. It might be a difficult task to get everything torqued and fit in such a precise manner but I thought that's why they charged a premium over Ruger, Taurus, etc.

You Tube Smith & Wesson Performance Center Part 3= This just might be the guy LOL

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Stang1911

On the adjustable sight guns, there is an alignment mark: the groove for the rear sight and the rib on the barrel. On fixed sight guns without ribs on the barrel, it's less obvious. There really isn't a torque spec as such, the torque is reached by angular travel spec.

It's harder than you think to get the alignment marks dead on. You're a wee bit short and you add torque until the barrel moves and "OOPS!" You're not supposed to loosen and retorque but it can be done (but the factory generally won't). A goodly application of moly based chassis grease does help, but it's still somewhat of a problem.

There is a spec on the number of degrees the front sight is allowed to be off, don't remember if I ever knew. It might be an aesthetic issue, but if if the sights can be zero'd it's close enough. Before you whine too much, remember the factory gets roughly 40% of MSRP when they sell the gun. [And I've seen some guns from the mythical good old days with much worse mechanical issues.]