Yea I'd just be taking some drill rod, cutting a crude mill face on it, tape or heat shrink tubing on the rod to protect the barrel, mill through the Bullet, dump the powder, neutralize the primer, then hit it.

Pounding on the bullet is likely compressing the powder outwards just as much as rearwards. Helping it bite the chamber. The powder would also dull the impact.

Having a straight solid shockwave to the inside of the case head would be much more effective.

We're dealing with lead and copper. You don't need and fancy drill rod or mill. And mild steel rod with a crude mill face cut into it with a zip cut will do the job.