I just picked up five 2/3 scale IDPA steel targets from MagnumTargets.com. They are 3/8" AR500 with predrilled 1/2" holes in the corners and one square hole punched center of the "neck" for 1/2" carriage bolt.
My stands are: 5 gal bucket with 60lb sac-crete and a 4" piece of PVC. Target is bolted to a 5' 2x4, which slips in the 4" PVC. The 4" PVC and 2x4 (actually 3 1/2"), lets the target angle slightly forward, to aid in deflection. I shoot "middle of the road" LSWC reloads in .45ACP. At 12yrds, 8 rounds rapid fire doesn't even wiggle the target...so no worries about knocking the bucket over.
I would say, for full power large cal's, I would not bolt the target solid. Hanging would allow for a slight swing and allow for better energy absorption. This would prevent the steel from denting or warping from constant center shots.