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Weren't there more than one iteration of the Ruger PC carbines, with significant differences between them?
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I'm not sure how you're defining "Ruger PC carbines," but I'll see if I can over-answer your question.
In 1960, Ruger introduced the Model 44 "Deerstalker." It was a gas-operated semi-automatic with an 18.25" barrel and chambered for .44 magnum, which it fed from a 4-round, tubular magazine. This pistol caliber carbine was discontinued in 1985.
In 1996, Ruger introduced the "Police Carbine," which was available in either 9x19mm (PC9) or .40 S&W (PC4). These were blowback-operated, semi-automatic carbines with 16-inch barrels, and optics can be mounted using Ruger's integrated base and proprietary rings. They fed from the same magazines as the Ruger P89 (9mm) or P94 (.40 S&W) pistol. This pistol caliber carbine was discontinued in 2007.
In 2000, Ruger introduced the model 99/44 "Deerfield Carbine." This was another gas-operated semi-automatic chambered for .44 magnum, this time with an 18.5" barrel and fed from a 4-round rotary box magazine (similar to the system used by the 10/22). This model was discontinued in 2006.
In 2017, Ruger introduced the "PC Carbine" (Pistol Caliber Carbine). These are another blowback-operated carbine, but this time they have a 16.25" barrel, which is threaded, and they are all takedown models. Optics can be mounted via the picatinny rail on the top of the receiver. These carbines are available in either 9x19mm or .40 S&W, and they come from the factory with one Ruger SR-series pistol magazine, which is what the rifle is set up to take. The PC Carbine has the capability of being easily converted to take Glock magazines and come with the part necessary to make the conversion. It can be reverted back to compatibility with the original Ruger magazines as easily as they can be converted to take Glock magazines. The 9mm version of the PC Carbine is also compatible, from the factory, with Ruger Security-9 magazines, although the Security-9 is not compatible with the SR9 magazine that comes with the PC Carbine, and there is a magazine well insert available from Ruger to make the carbine compatible with magazines from the Ruger American pistol. The PC Carbine is also available with a variety of buttstock, grip, and foreend configurations.
I suspect your question pertains more to the 1996 "Police Carbine" and 2017 "Pistol Caliber Carbine" versions, so a short summary of their differences:
1. 1996 version compatible with Ruger P-series pistol magazines. 2017 version compatible with SR-series pistol magazines, Security-9 Magazines, and Glock magazines with what comes in the box and American pistol magazines with a $30 part from Ruger.
2. 2017 version is a takedown model (all of them). 1996 version is not.
3. 2017 version has threaded barrel from factory, 1996 version does not.
4. 1996 version uses proprietary scope mounting system, 1996 version uses pic rail.