Here's a great post on this topic. Sounds like he knows what he's talking about......
Not to highjack the thread, but the subject came up...
I’ve shot handgun on metal targets since 1974 or so. I know I’ve personally fired over 20,000 rounds on metal targets in that time and supervised (ran the match) many times that many. I have one colleague who has supervised and shot a lot more.
The primary value of a metal – gong – target is ease of scoring. If it makes a sound, you hit it; if no sound results, you missed. In practice sessions this gives immediate feedback to the shooter.
On a flat metal surface more or less perpendicular to the path of the bullet, bullets do not ricochet. Handgun bullets fragment on impact, even fully jacketed bullets. The fragments fly off the face of the target along the face of the target. Anything to the edges of the target will be peppered with fragments; dangerously so up close. The fragments fly in a 360 degree pattern, parallel to the face of the target. If the fragments hit another solid surface, one obtains a secondary splatter effect. So, metal targets should not be hung over concrete pads or a metal plate. A bullet fragment splattering off the target can be secondarily deflected back to the firing line. (This is the usual cause of ricochet hits in indoor ranges; sort of a two or three cushion shot back to the firing line.)
Another, very serious form of ricochet is from a cupped or cratered metal target.
Metal targets suffer from three forms of damage. All are annoying, and all can cause fragments back toward the firing line.
Craters or cups in metal targets are the most dangerous. By cup, I refer to an indentation that does not penetrate the plate. Cups are usually formed by impact of a large heavy bullet. The resulting indentation can – on the next hit – allow the projectile to slide down the side of the cup, be turned in the bottom and slide out of the cup right back at the firing line with little loss of velocity. Even if the bullet hits the bottom of the cup and shatters, the sides of the cup direct the fragments back toward the firing line.
Holes in metal targets are typically caused by high velocity impacts. Various strength metals have different limits, of course. What works well for moderate handgun rounds can be cratered or punctured by a top end .357 Magnum load. A .30-30 rifle, pedestrian as it may seem, will put about a .40 - .50 inch hole in quarter inch mild steel plate. The resultant hole will almost always have a raised rim around the entry side. This raised rim will fling minor fragments back toward the firing line, usually at the unnoticed to annoying level. Depending on the size of the rim, this could be potentially dangerous.
The round that penetrates steel can peel off the jacket and the jacket can be ejected in any direction. I have witnessed one minor injury from a jacket bounce; a small but rather painful cut on the forearm requiring a stitch or two to repair. Being hit in the eye with such debris would be catastrophic.
The third problem is the bending of the plate. Shooting mild steel or boiler plate with non-penetrating rounds is pretty much like beating on it with a hammer. Sooner or later, the plate will start to bend under the impact. Turning the plate around and shooting the other side will beat it back flat, more or less.
I am not a metallurgist. I once knew what kind of plate to ask for at the metal yard, but I’ve forgotten. The good news is the people at the metal yard know about it and will direct one’s attention to the material best suited.
For general handgun use, I suggest nothing thinner than three-eighths inch thickness. Rifle targets should be thicker for longevity. Again, talk to the man at the metal yard.
If you know anyone with experience building a silhouette target set, they are an excellent source of information.
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There ain't no free lunch, except Jesus.
Archie
Just be prepared as it will happen. Should make you rethink your eye wear choice being certain that your lenses are an unbreakable polycarbonate material...