Found them on sale at Dick's, $4.88 for 20. 12 ga, 2 3/4in, 7/8oz.#8 shot. On the back of the box, it states that the shot is "hardened". Is this lead, steel, or something else. Ultimately, are these shells safe for use in my 1960 model 37? If not pure lead, then I don't wish to use them at all.