And sometimes old farts are exactly that. There are at least 3 reasons you shouldn't do this.
1) Rifle primers are more powerful than pistol primers because they have to be when used with large capacity casings. I recently did an experiment with pistol vs rifle primers, small and large. I shot some rubber primer-powered bullets across my chronograph. The rifle primers yielded considerably more velocity. So you would be on your own if you try to extrapolate a "good" load based on any published loads. Injury to you, your gun, or anyone next to you is possible if you guesstimated wrong.
2) Rifle primer cups are made with a harder alloy since rifle firing pins generally hit the primer with more force. There is the possibility that a pistol firing pin may not ignite the rifle primer or even worse you could get a hang fire. Is this a high probability? I don't think so, but why take the chance?
3) Why do it? Have you had any problems when using pistol primers in pistol cartridges?