I've had a Rock Island Armory 1911 .38 Super since 2016. Mine is nickel plated, and it's plated inside and out. That reduced some critical dimensions and made it very tight fitting. It's finicky about chambering cartridges; I have to pay close attention to bullet sizing, seating so the base of the bullet ogive doesn't jam against the bore throat, and run them through a Lee Carbide Factory Crimp Die to make sure the outside cartridge dimensions will fit. The groove diameter is .352". It handles jacketed loads slick as a whistle. It's more accurate than I am. I've used Starline Super Comp brass from the beginning and never had a round fail to eject properly. RIA lists the extractor as the same part for .38 Super and 9mm. I have a lot of WC820 and Accurate #9, and run 124 & 125 grain bullets at about 1300 FPS for jacketed, 1350 for cast. Hodgdon's data indicate you can get a little more speed out of Accurate #7, but I've never tried it.
The semi-rimless case is what John Browning thought best for auto pistol cartridges. The early .38 Automatic colt pistols headspaced on the rim and supported the rim around most of its circumference. The semi-rimless cases worked fine there. Those pistols became obsolete in the 19209s and sales were low, but there continued to be some demand for a .38 Auto pistol. When the idea to make the Government Model in .38 Auto as a replacement for the old model .38s came along, they continued headspacing on the rim as they always had, but the feed ramp and extractor took out too much of the surface the rim seated against, making the rim support unstable. That didn't get recognized and corrected until BAR-STO made barrels headspacing on the case mouths, I think in the late '70s or early '80s.
As for the confusion about nomenclature, when the converted Government Model came out, it was "Colt's Super .38." That was the gun name. The cartridge it was chambered for was the old .38 Automatic. Originally it was loaded with 130 grain bullets at a rated 1190 FPS and Colt advertised it as "Almost 1200 FPS!" After the Super .38 pistol was brought out, it was realized that it was a much stronger pistol and could handle higher pressures and velocities. Remington brought out ".38 Super Automatic" cartridges loaded with 130 grain bullets at 1275 FPS, which was long the standard. FMJ, SP, and JHP factory loads were all available. Maj. Julian Hatcher opined in The American Rifleman when the Super .38 was announced that it would be useful for lawmen who needed to have capability to penetrate "bulletproof vests" and car bodies. It had long been recognized that the old 1900 Military .38 Auto and its derivatives weren't strong enough. The wedge that stopped the slide could break and let the slide fly off to the rear and hit the shooter, much as some Beretta 92s did later. So the standard .38 Auto was downloaded to a muzzle velocity of 1060 FPS and max pressure of 26,000 PSI. .38 Super cartridge boxes always carried warnings to only use them in Colt's Super .38 and Government Model pistols, but lots of folks never read or follow directions. In 1974 SAAMI added the +P designation to the .38 Super as an additional safety warning. That doesn't mean they're loaded to higher pressures than .38 Super ammo without the +P designation. I notice that advertised factory ballistics for .38 Super cartridges now are mostly down to the velocity of original .38 Auto cartridges, doubtless for liability concerns with old .38 Auto pistols in the hands of ignorant owners.
I have .45 ACP and 9mm pieces aplenty, and I know that there isn't a big difference between hot 9mm Luger and .38 Super performance. There's a limit on pressures in .38 Super because the standard 1911 design leaves a bit of the case wall unsupported over the end of the feed ramp. You'll see a bulge in cases there if you get too enthusiastic with your loads.
My opinion formed when I was a child drooling over Shooter's Bibles was that a Government Model in .38 Super with nickel plating was the epitome of an automatic pistol, Browning High Powers with Renaissance engraving notwithstanding. I still feel that way. The .38 Super will always be a classic to me.
