With the same diameter pistol bullets are safe.
First problem is to find a correct/safe loading for that weight of bullet. Something close and lighter will work and load light.
Second problem is the bullet it's self. Pistol bullets are designed to do there thing at lower velocities. Moderate velocities from a rifle is going to be fast for a pistol, The possibility of complete disintegration of the bullet is there. Followed by the shedding of the jacket. IF the bullet reaches the target it could very well blow up on target. That sounds neat at first but do you want to skin your target animal and send slivers of lead and jacket into it's body to fester?
As stated in the previous posts, stability could very well be a major problem.
Unless you have great numbers of pistol bullets to waste (you can send them to me
) I don't see any more value in this exercise than an interesting experiment. I think paper patched cast lead bullets would be a better way to experiment.
That said, I have played with some and they were fun to play with, not very functional but fun. Cast 75 grain .32 S&W bullets out of a .303 British, didn't have a crono at the time but they would hit paper at a hundred yards.
Enjoy and be safe.