Can 1911 .38 Super be converted to .40 simply by changing barrel and magazine or is there much more involved?
Pretty sure you would need a different slide.
The breach face on the 9mm/38 Super slide probably would not allow a .40 case head in by the extractor.
Assuming that the frame's feed ramp is adequate, it boils down to which manufacturer made the slide. In my experience, Colt slides will work for both 9mm and 38 Super, but not 40/10mm. Springfield slides work for the exact caliber specified. Kimber slides work for 9mm, 38 Super, 40 S&W, and 10mm. That may have changed over time as manufacturers are constantly changing their specs.
Depends upon manufacturer -- That seems to be the truth.
Kimber tells us that they use the same slide for 9, 38 and 40.
They say different ejector & barrel, but extractor and firing pin are common among them.
I don't have a Kimber so I didn't try it myself.
I tried a Colt and it doesn't work.
I made a 40S&W dummy round for testing.
I put a spare 45acp barrel in the 9mm slide with a standard bushing.
I used a 45acp magazine also.
It fed up the ramp toward the chamber and tried to slide under the extractor.
But the breechface didn't fit. Extractor was too close to centerline.
The rim was too wide and it stopped on the extractor.
Since I had the extra parts, the experiment didn't cost me anything.
Like others said, my Kimber 38 Super had a .40sw breachface. So I converted mine to .40sw with a Kart barrel and new magazine. You might have to retune the extractor and maybe adjust the length of the ejector...depending upon how it ejects.
The first non-Bren 10 pistol in 10mm (same head diameter as .40) was a gunsmithed Colt .38 Super. BUT the gunsmithing included opening up the breechface.
As said, if you have a Kimber you can probably do it with a barrel change, if not, not.
Thanks for all the info. Interesting about the Kimber slides.