I have shot post challenges, I assume the 2 X 4 match is the same. You shoot at a piece of lumber with one end planted in the ground until you knock it over, the top has to be on the ground, not just leaning over to stop the clock. No limit on bullets, just race the clock. Accuracy is everything, you cannot cut it in 1/2 unless you can place the bullets so they act like a saw. We shot 4 X 4 with three man teams. Three guys try to saw it off near the ground. When it is nearly cut through, the middle guy, usually with a heavy bullet .45 load, starts shooting near the top like a sledge hammer while the side guys keep sawing the bottom. Pretty fun way to burn a lot of ammo in a hurry.
We use to do that with sections of 4x4 s. The .45 acp is deffinately the king fo this and use what ever ammo shoots good and cycles well in your gun. 230 grain ball is a better choice than some of the lighter bullets that don't penetrate as well. The trick is to shoot a string of rounds in a nice horizontal line and have a partner(s) that can do the same. Should be able to cut the board down with a single magazine from two shooters. Well aimed shots get the job done much better than spray and pray.
Rickk55, here is a link for an outstanding 45 acp bowling pin bullet. http://www.pennbullets.com/45/45-caliber.html
The 230 grain TCBB truncated cone bullet is awesome. The 225 grain WCBB has a much wider meplat and will do more damage. However, it is hard on the frames of 1911 pistols. Choose your recoil spring correctly. It should be fine in your revolver.
The 270 grain Thunderhead is an interesting bullet, but I'm not sure if it is usable for 45 ACP. You can call Penn Bullets for loading info on any of these bullets.
Now, if the idea is to knock the 2x4 over and onto the ground, I'd use the 230 truncated cone bullet in a 1911. However, if the idea is to cut it in half, I'd use this bullet, the 152 grain SWCBB. It is low speed stable, but you want to push it 1100fps or higher. You want to splinter that wood, not bore holes in it.
Now, if you want to shoot jacketed I'd recommend the Federal Premium Tactical HST 230 grain unit in standard or +P. These bullets seem to expand in anything.