Not only charged with armed robbery (because the victim had a reasonable belief you were armed), it also gives them the legal right to use lethal force to stop you, i.e., shoot you dead on the spot. It simply doesn't matter whether you actually had a gun or the gun was loaded or real. They BELIEVED it was real and you're just as dead. Some incredibly stupid criminals have chosen to die that way.
Also, not clear why what you mean by "charged with murder" if you didn't do the killing. Yes, there is such a thing as "inchoate" crime (aiding and abetting or conspiracy to commit murder), as well as "felony murder" occurring while you're engaged in any other felony that results in death.