The ammo tins that I have dealt with always had the little key spot welded on top. You simply use the key to unwind the metal seal.
Of course, after about 3 inches the seal breaks. So I resort to hammer and metal chisel. After chasing the tin around the garage floor for 20 minutes (it slides several feet with every impact), ripping open an additional 2 inches of the seal... along with three fingers... one thumb... and the fender on my wife's car after I flung the chisel in disgust... I get the ax.
After a dozen or so good whacks the tin is squashed down on one side really good. This doesn't help get it open but it is very satisfying. As I raise the ax for a truly mighty blow the head flies off and takes out the windshield on my truck.
At this point I usually give the tin a good kick. Of course, this does nothing to help get it open but it gives me a few moments to think about my next move as I hop around on one foot in agony.
I proceed to hoist the tin up and apply the edge to the spinning wheel of the bench grinder. But long before any serious progress is made in opening the tin, the metal gets hot from the friction. I'm so intent on the metal cutting process that I don't notice the heat building up until I burn my fingers and drop the 40 pound tin... on my remaining good foot.
Thoroughly disgusted now, I pick up the battered tin and hobble over to the trash can. Raising the uncooperative ammo tin over my head I smash it into the trash can as hard as I can.
This causes the seal to pop off and all 500 loose rounds spill out into the bottom of the trash can.
I spend the next 15 minutes scooping out the shells from the stinky trash can, cleaning the rotted garbage from them as I load them into plastic storage boxes. As I am placing the last cartridge in the box, I notice the head stamp.
I bought the wrong caliber.