About 2" diameter patch that is slowly washing out with tiny dribbles when it rains hard. I figure on chipping it out and using hydraulic cement to redo it, but I got an idea in my head. (That's where it usually goes bad).
Rather than slowly chipping it out with hammer and chisel (I don't have a hammer-drill) what do you think would happen if I hit it with my 7mm mag? I know cinder blocks and such fly to pieces, but I've never fired at poured concrete. (That's guessing that I don't exactly center-punch the patch). Will I just make my patch job bigger if I do this, or is it a viable option to the chiseling?

I'm going to say. 7mm Bullet impacting concrete at short range makes for a Darwin moment.
So. Bad idea.

Make sure you have a buddy there to hold your beer and run the video recorder.

If that was a good idea they would make similar tools like that for that use.

Since they don't my guess it isn't a good idea.

Quoted: If that was a good idea they would make similar tools like that for that use. Since they don't my guess it isn't a good idea.

I hadn't thought it that way. Probably right.