About 5 yrs ago when I was doing wetpack testing of ammo, we tried to simulate the sternum bone with some tests. Best we could determine was 3/4" of plywood was close to the approx. 1/8" sternum based on compresive strength. Much of the calibers we tried did penetrate the plywood and continued several inches, enough to possibly reach the heart in a real event. Plus, lots of "shards" came out the back of the plywood! Even .25acp FMJ penetrated but not .25 JHP. Higher caliber JHP did in most cases.
In no way are these comments supposed to be "certified". But if you want to try your ammo, get a piece of good, exterior grade 3/4" plywood and see if it penetrates.
My tests were posted on the old usrange site which is no longer available.