Back in the old days, certain MFR's made some of their .40 & .45 slides
the same size, and made the .40S&W barrels FAT as the .45acp's...
Cute trick, eh?
So basically some folks ended up with .40-S&W bull barrels so
that the MFR's could save a buncha bux
(If you don't believe me, take a good look at
S&W's Chief's Specials in .40 & .45!!)
This is the only place I can honestly say that Glock totally failed.
As they should have done that with their G20, G29, & G40,
which all should have had bull barrels so they could use
G21, G39 & G41 slides and saved themselves a buncha dough.
Now this was also done with 9mm to .40-S&W when they
started making .40's, as they had no idea how hard
.40 was going to be on slides and frames (mostly slide stops),
Star's famous Firestars were a great example of this,
as the Star M43 (9mm) & M40 (.40-S&W) used the same frame
and slide, but the only differences in them were the Barrels,
Recoil Springs & Hammer Springs!! This worked pretty well,
as long as you changed out the .40 recoil springs
every 2500-3000 rounds...
These are just a few examples of folks saving a few bux...
but there are probably far more examples out there