If you're just target shooting, 30-30 bullets will shoot just fine in a 30-06. I used to do it all the time, just for plinking loads. You can load them at -06 power levels also. It will not harm the gun. What the velocity limits would entail would be if you shot the bullets at game, like deer, etc. The higher velocity impacts would cause the bullets to come apart like a varmint bullet when they struck the deer, causing massive surface damage, but very little penetration, and likely crippling or wounding the deer.

I used to load 150 gr flat or round nosed 30-30 bullets for my -06 and go jack rabbit splatting in the desert all the time. I even shot a few coyotes with that combination. Great fun and great practice.