There aren't really "prop guns". Mostly they are real guns loaded with blanks. That's how Alex Baldwin killed that guy. In addition, a lot of rubber dummy guns are real guns, but filled internally with rubber, so the barrel would still be metal (and not crooked)
Prop just means property of the studio. As the Alec Baldwin incident (He shot two people and killed a Woman) and Brandon Lee (Son of Bruce Lee, who died from a similar accident on the set of the Crow) They often are real guns. In particular Revolvers guns are the more likely to be live on TV and movies. This is because of the way they operate vs automatic or semiautomatic weapons. Automatic or Autoloaders use gas pressure to cycle the operating system of the weapon. Now TV and Movie directors love automatic fire. They love from the hip spray and prey mountains of spent brass automatic fire. Blanks don’t on their own produce the pressures needed to cycle the weapon. To get around this Movie makers use three tricks the first is a gun that is just a shell with a Spark plug in it. That’s used for really cheap sci-fi movies with sci-fi guns, others do it post production with sound clips and flash FX. In this case the Barrels of Prop rifles like the T97 used in Stargate Universe have their barrels replaced or plugged. The new “barrel” has a far narrower opening and different means of gas block so as to increase pressure for the weapon to cycle. Military weapons modified for training do the same but with an external adapter.
Revolvers don’t have this problem as single action or double action it’s using mechanical means based on the hammer and or trigger. On a single action you pull the hammer back to full cock and pull the trigger the hammer drops, if you hold the trigger down and fan the hammer the gun cycles. In a double action, you pull the trigger you are in the first stage pushing that hammer back until it hits the point of full power and then the hammer drops.
Rubber guns or Stunt guns are not real guns they are a rubber sculpture of a gun. They are often used as live weapons are heavy with the potential to be damaged or damage in a stunt or in a case where the point is just to fill a scene with out the need of detail of a real gun.
The RCMP ordered the first batch of Type 97 rifles imported into Canada to be confiscated and destroyed presumably with the ones owned by the studios exempt because they would be blanked and placed in tight controls. This is as the trigger pack was built with a seer that at least in theory would allow conversion to full auto. Something similar happened in the US to Romanian PSL rifles a seer in the wrong place and boom all the rifles had to be destroyed and any new ones redesigned. Even if conversion of PSL to Full auto would be completely idiotic.