I have shot tens of thousands of rounds at my two 12" inch gong targets Ninety nine percent were pistol rounds. I have gone through several variations, the discs have grown from eight inch now to 12 inch. Eight inch diameter plate was just too hard to hit at 50 yards. Plate thickness is 1/2" and the whole target must weigh 40 to 50 pounds! Gets heavier every year!! My targets have welded joints. I tried chains and they came apart very quickly. If hit, they broke sooner. I found that I must use the heaviest bar I could, about 1 inch was the minimum, 1 1/2" better. Three quarter inch bar stock would fracture fatigue just at the plate rim. The swinging attachment, currently a pipe, that will fatigue fracture and so will the joints. Weld joints last a few years with pistol ammunition. Rifle ammunition is very hard on the target. Early on I tried shooting at the things at 150 yards with miltary ball. Two hits that almost went through these mild steel plates was enough to convince me that FMJ was a bad idea. Even jacketed HP will create craters. The closest I will shoot at the things with rifle cast bullets is 100 yards, and still, the shock is enough to bust welds.
I don't remember if this broke with 303 Brit cast bullets or 30-30 cast, but anything going 1700 fps hits my targets hard. I do remember shooters at the range laughing when the pendulum fell off.
I am of the opinion that with a rifle, 100 yards is a minimum distance due to the velocity of the splatter coming off the target, and the violence of the impact on the target. Even 50 yards with a handgun will raise complaints at my range, depending on the way the wind is blowing. I was shooting one day, a stiff wind blowing in my face, at my gong target at 50 yards. Lead fragments, lighter than tin foil, smaller than ground pepper , had been blown up, caught in the wind and fell on people easily 75 yards from the target. At most they felt something like fleas landing, but these characters were outraged, went to the next club meeting and demanded that steel target use be banned from the Club range! So, be aware, very light fragments will drift in the wind and infuriate those who don't like the sound, and already dislike steel targets because they believe shooters should only be shooting at paper targets.
I have seen steel targets absolutely chewed up with high power rifle bullets. But a few shooters have brought out modern steel plates and hit them in my presence , at 100 yards, with high power bullets, and upon examination, no indentation. So, I don't know. I do know a bud who managed the El Paso Shooting Club range, he claimed every steel target he put out, to 300 yards, got shot to swiss cheese. He was able to find armored personnel carrier hatches, and those were shot up. He said his best solution was to buy junked engine blocks and let the rifle shooters chew those up. The blocks were cheap.
The closest I shoot pistols at my gong targets is 25 yards. I think everyone ought to be able to hold 12 inches at 25 yards, most of the time,
and that is far enough that the big lead fragments all fall within 10 feet from the target, which adds a lot of space between me and any lead splatter. Lots of people have misconceptions about ricochets and steel targets. At least with pistol bullets, I have shot tens of thousands of lead, JHP, and FMJ. These bullets fragment, similar to a snow ball hitting a brick wall. The bigger the bullet, typically 44 and 45, what is left is the size of a nickle. Smaller bullets, 38, 9mm, what is left at the foot of the target is dime sized, at most. Plated bullets act similarly. I sometimes find 357 JHP jackets split like star bursts, I find them up to ten feet, depending on the wind, but no lead core inside. The jacket is light and will drift with the wind. My targets are up, about four feet up, so any bullets that miss, go into the berm. It is dangerous to have bullets skip on the ground, you cannot predict where they will land.
I am interested in reading about better designs.