I made a metal gong for my 500yd range and have shot it several times with my .243 using 95gn Ballistic Tips, my 6.5-284 w/120gn B-Tips, a friends .270Win w/ 130 & 150gn SP. None of these dented the 1/4" metal but they did splatter and knock the paint off.
I shot it with my .300WinMag using 180gn B-Tips and it went through it like hot butter. The metal didn't even have "pull" marks, it looked like it had been drilled through with an AC drill!
So I was thinking the rest of these rounds are pretty whimpy and what a stomper that .300WM must really be. Then, then, then I loaded some 140gn AccuTips (Remington) ahead of 51.5gn of RL22/BR2 for my 6.5-284Norma and slung it at my gong. They went through just as effortlessly as the 180's from the .300 did. I am impressed with the 6.5 to say the least.
Here is a picture of my gong. Those bullet holes you see are from the .300WM. I wasn't really shooting for groups but both turned out pretty good. I really just wanted to hear that "smack".
I haven't taken another picture of it since. The orange circle is roughly 5". JohnnyK.
Good luck with your decision.