I remember being told by someone at S&W that they'd sold a fair amount of their 3rd gen pistol parts to Jack First, but you'd have to call to see if they still have them (aren't listed on general web page).
About us – Jack First Inc.
Dunno what extractor springs the PC used in their 945's, but the standard 3rd gen .45 extractor spring is plain unpainted steel, and the last new ones I was sent that were "extra" were painted blue.
I'd like to see a pic of the
ejector, just standing proud above the frame (sans slide), to see if it's an old or revised style, and to see if the tip is intact (old styles could develop a stress riser and break off over time).
Ordinarily, if an extractor spring is
too lightly tensioned, it can sometimes fail to stay held against the case rim during a critical moment in the effects of the recoil impulse (when the barrel separates from the slide). Someone at the factory once called this a critical "moment of mass", because the "mass" of the pivoting extractor head, pushed against the case rim, has to be prevented from being pushed
away from the case (recoil force acting on it), and the spring needs to counter this force. If it doesn't, the hook bounces out and away from the case rim, and the empty case may stay in the chamber.
I can't speak to anything used to measure the spring tension other than the dial gauge recommended and sold to armorers by S&W training. I'm not a machinist or gunsmith, just a factory-trained armorer. You might contact forum member BMCM, as he's better equipped and experienced as a machinist.
Also, as I was once told by the good folks at Wolff Gunsprings, when I asked why their "tension ratings" for their S&W extractor springs were listed with different ratings than what we were given by the factory, some companies might measure "tension" differently, using different equipment and methods.
If you can source your factory extractor springs by S&W factory parts numbers, these are the numbers of the springs listed in the .45/10 3rd gen's:
Standard - #10202
Heavier than Standard - #23563
Extra Heavy - #23433
(The complete part numbers often had 4 zero's at the end, so #10202 would be #102020000)
Since the people who originally built the 945's have retired, it's not surprising that someone at general customer service might say they don't support them anymore. You could try calling and ask to be connected to the PC, itself, but I have no idea if anyone working there at present was there for the heyday of the PC and their hand-built pistols. (John and Vito are retired.) It would be a roll of the dice whether there were even any of the older parts used in those guns remaining in some bin, desk drawer or cubby hole.