The manual safety assemblies are "parts bin" parts for the most part, but you have to take into consideration the wide range of manufacturing and production changes that have occurred across the 3rd gen line over the years (and even in the earlier models). There were still some machining operations controlled by hand in the early 3rd gen production which were later replaced by CNC equipment. Some machining cuts weren't as precise or as easily done with the earlier manufacturing methods. The length and precision of the relief cut under the extractor recess in the 9/.40 guns is an example, as is the depth and shape of the extractor spring hole in the slide.
This can make for some parts tolerance & variance issues where a particular part that fits and functions as intended in one particular gun might not be as good of a fit in another gun. That's why armorers keep spare parts on hand and always check for proper fit & function, even with "drop in" parts. I've even had an occasional newer production barrel provide not quite acceptable functioning in one gun, but work just fine when used in another gun.
The newer sear release levers are being made to much closer tolerances since the newer production 3rd gen guns have been made to increasingly better tolerances, but that only means that it usually takes fewer file strokes and checks in order to fit a new sear release lever in a gun. I remember when the levers were made with a lot of extra metal on the bottom "foot" where the filing was done, because of the wider range of variation sometimes encountered due to machining and tolerance stack in various production vintage guns. It often required a lot of file strokes, done 1-2 at a time between reassembling the gun and performing the bench checks to see if the proper timing had been achieved, and then taking it back down to the point needed to remove the lever and make another stroke or two. It's usually faster and easier nowadays with the newer parts.
The extractor and sear release lever are the only parts left that are considered fitted parts. Barrels not often anymore, and I've only had to file the radius of a drawbar head once in all the years I've been maintaining & repairing 3rd gen guns.
Armorers are provided with gauges to use to make it easier to check for the proper tolerance and function when fitting the extractor & sear release lever. Checking for the proper decocking timing used to be done by 'eyeball' and careful, slow manipulation of the decocking levers and hammer manipulation, but in more recent years S&W has taught armorers to use a set of 3 gauges to check for decocking timing - made from numbered drill bits, where the non-cutting shank end is the "gauge" - which are used for Go/No-Go checks when the sear release lever is being fitted. It's easier and quicker to teach and easier to do for newer armorers at the bench.
I remember one time when I was thinking about replacing the ambi manual safety in a very early production 6906 with a single (left) side assembly. I just happened to have a single side assembly removed from a CS9 (because the CS9 owner had wanted an ambi assembly in his gun and it was before the CS guns started being produced with the ambi assemblies as standard parts). While the assembly fit and functioned within acceptable tolerance in the 6906, successfully passing the bench checks, I didn't care for a slight bit of looseness between the assembly and the slide occurring when the lever was being depressed and returned upward. The assembly moved within the slide more than I felt comfortable with, and I decided not to use that particular part in that particular gun (which was a dedicated service weapon, after all), and since I didn't have any other single side assemblies at hand to try at that time I simply remained with the original ambi assembly.
The only reason I wanted to replace it was that the ambi lever was chewing holes in my suit & sport coat linings at work. I was wearing an open top Kydex holster back in those days, before changing over to a leather holster with a retention strap that covered the ambi lever.
Sorry for the rambling.
A gunsmith familiar with S&W TDA pistols can probably make the relatively quick exchange of the manual safety assemblies and check to see if the sear release levers have to be replaced in either gun. S&W can naturally do it, but it probably wouldn't be considered a warranty repair and might cost you shipping. Dunno. You might call and ask.
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Ret LE Firearms inst & armorer
Last edited by Fastbolt; 11-20-2010 at 03:50 PM.
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