One possible reason would be because the screwdriver you used wasn't the correct size. If there is space/room/slop so that is isn't snug against the sides of the slot, you can and inevitably did damage it. Screws can be purchased at vendors like TopGunSupply.com and if you choose, you can get hex head screws. Be careful not to over tighten them when putting them back. A tiny dab of Lock-Tite is what I use on mine to avoid any possible backing out without my permission. Over tightening could also strip out the threads and may even cause the screrw to protrude into the magazine well. Thus opening the possibility of scraping or otherwise damaging your magazines or making the insertion/removal less than "butter smooth".