Ronald Reagan and James Brady were shot with a .22lr revolver which Hinkley had purchased shortly before the shooting.
HOWEVER, Hinkley also owned, and had owned for some time, a .38spl revolver. Had he not gotten the .22 and instead used the .38, Reagan and Brady would have been more seriously injured if not killed.
BTW, from what I recall, Hinkley got the .22 because he wanted to use some gimmick ammunition called "devastators" or something that was supposed to explode on impact but was only available in .22lr. Fortunately, he was unaware that such ammunition must be accellerated relatively slowly in a firearm barrel (or else it will detonate in the gun) and thus, when fired from a handgun, will thus not reach high enough velocity to detonate upon hitting its target. Also, even if he'd used a rifle, I would expect that a 120 grains of lead at 1000fps would do more damage than 30 grains of lead at the same speed combined with a few grains of powder.