hey guys, new to the forum but love it so far, i picked up an ar 15 last night with 2 uppers, i pull the badger latch back to open the bolt but it will not stay open. i have no idea where to start with it, and yes i am making sure the mag button is held in by my finger when letting the bolt go to catch. it feelsd like it might be worn out but supposedly the round count was only approx 100 rounds on the lower. its a bushmaster lower. any help would be great.