i just bought a used bushmaster ar-15 model.. XM-15 -E2S,and i don't know much about them but i bought it for 750?? good price?.. the main question i have is on the stock?? when i shorten it all the way up the end sticks out of it?? just dos not look right... anyone help please ! also when its out there are threads looking like it need screwed in more??? please help i have no clue what is going on with this??