Found a box of Winchester 357 metal piercing at a flee market. Never seen this before, does any one know about these rounds . Would they have been shootable,they were in a older white box,they looked clean . Had to pass them up this time .Need to know more first,before a purchase. If i even see them again.

Are they pointed conical fmj? If so, I shot a box full years ago. No problems and I didn't chrono or even test for accuracy. Just shot up an old junk car( I did mention it was years ago, right?)
They actually only dented the bumpers and did not penetrate. Went thru the rest of the car ok, but then most .357 mags will.

These were made primarily for law enforcement, probably 50's or 60's vintage. Should be fine to shoot, although 357 from that era seem to be a little hotter to me. They should be 158 gr., meant for shooting thru car bodies and engine blocks, although I have no idea of their effectiveness for those purposes!

Here is a link to a thread about the same topic and ammo I posted a couple years ago. If the box is in good condition and has all or the majority of the rounds, it is fairly collectible. I was lucky to get some .45 acp, which is the most scarce. People say each round is worth $2-3 but I have yet to see or here anybody pay that much. But I would say $1-1.50 a round is more reasonable. I would buy them if you see them, just the advertising "metal-piercing" will always draw interest.

.45 Metal Piercing ammo

I found a half box of .357 metal piercing rounds a few years back while going through my Dad's stuff. While up at my friends hunting cabin I set up a few steel plates aluminum plates, and blasted away. I was quite disappointed that the ammo did not pierce either and now think that the "piercing" factor was more hype than reality! Maybe through sheet metal results would have been much better, but then again just about any .357 would do the same. If steel plate piercing is needed, I would opt for a rifle and pointed jacketed full power ammunition.

Automobiles were made of much thicker US-made cold rolled steel back then. I remember an old 40s car (Caddy?) up in the woods behind our house. .22 shorts would put a good dent in it unless fairly close and dead square. HVLRs would go through. Low brass 16ga bird shot wouldn't penetrate from a distance either..

Glass was probably thicker too.

Todays cars are paper thin , low quality steel or aluminum. Some are plastic! My Chevy truck has fiberglass sides on the bed!