Don't be to hard on us, Olympia. You bought a cheap, Chinese made, probably NC-Star-brand, soft-steel piece of manure. Even the screws are made of steel that's so low-grade that, if you put any kind of significant torque on them, the thread will be gone. It should come as no surprise that this chunk of fine craftsmanship flew off after a few rounds. In other words, yes, others have experienced the same kind of unfortunate outcome such as which you describe. Some may suggest putting a recoil pad on the stock, or reloading on the light side; in any case, I hope you'll keep your Mosin and enjoy the fine, historically significant, loud, recoil-robust milsurp it is (sans crappy chinese, useless add-on)!
Lou