Machines that make parts get out of spec, or at least they will hit one end of the set range of tolerance before they are adjusted. Cutting tools wear. They start off when new removing a tiny bit too much material, then as they wear, they remove less until they get to the point where a tolerance range is about to be exceeded. Then they are replaced.
All during this machining process samples are pulled at various times. They are measured to the 1000th of an inch to see if they are in spec. Most barrels are not actually measured for every dimension--only a representative sample.
The same process applies to slides. The front of the slide has a minor range of allowable tolerances.
When you get both parts at a maximum tolerance, right at "spec", you have a "stacking" of tolerances, which can create just the minor amount of friction required to seize the parts when other specs are also at max allowable. For instance, if other areas of friction were decreased, i. e., anything effecting slide velocity such as lack of cleaning and lubrication, then the two original mating surfaces might be able to slide over each other, especially if they are smoothed (polished).
So, can Quality Control at S&W be expected to measure every tolerance on every part on every gun during assembly? Not for under $400 per gun. Does S&W figure into their costs that less than 1% of their guns will be returned for minor repairs? Yep, just like every other major manufacturer trying to achieve tight tolerances.
One solution would be for S&W to widen tolerances. That, with stacking of loose tolerances, would lead to loose guns that would shoot reliably with poor accuracy. As they wear they would get worse. Your WWII military 1911's are an example of this. Loose tolerances are easier to make and assemble, quicker, cheaper. Unless extremely loose, they function very well, even with crud in critical places. Think original Glocks, not known for great accuracy but great reliability.
Today's pistol customer expects accuracy and reliability at a good price. That's a tall order for machined metal with lots of parts interacting at high pressure and high speeds assembled and inspected by humans.
I am not an apologist for S&W. I think this particular problem is identifiable during assembly and QC with some training, especially now that it is a known problem.
Or, adjust machine tolerance for this one area since it does not effect any other function, like TP has done. That has likely already been done and we won't see this problem going forward.
