It's not something I had considered before but do any of you guys keep spare parts in your gun bag? The reason I ask is today I went out shooting with a friend, the second mag I put into my Bushmaster wouldn't lock in. On inspection I noticed the mag release had broken, on the left side where the pin is swaged in, there isn't a lot of metal around the pin so I expect this could happen in time. (the rifle is 6 years old and had a lot of mag exchanges). It's a $15 part but put the rifle back in the bag as I didn't have a spare. I went on line and bought two lower rebuild kits and one upper kit. It wasn't that much $ and with the simple tools in my range bag will prevent this in the future.