Given that your 22 brief magazine has no markings It's not necessarily from Winchester. I have never seen a 22 brief journal which was not the same outside the house dimension as 22lr mag. I can’t picture how a mag, like you explained, could risk be protected when inserted. A https://highimpactrounds.com/product/winchester-super-x-12ga-2-75in-1oz-6-lead-shot-1290fps-25-rd-bx/