Ok guys this is my first post so take it easy on me. I did some research but couldnt find the info I was looking for. I have a DPMS A3 AR-15 and I just bought a new dpms A3 flat top upper reciver and I would like to swap my 20" barrel out to a 16" barrel. Im not really looking for a long range weapon cause I have my remington 700 for that. Im wanting a more SHTF close quarters weapon. I have 20 acres and I shoot alot here at home. I was thinking of going with a 16" Heavy barrel (not bull barrel) but not sure what the best twist for me is. I shoot remington 55gr cause its clean, cheap ammo that I can pick up at wally world 100 for 45bucks. Could some one explain to me why I should want a certin twist. Im young and still learing about the barrel twists. Also I know I will need a shorter gas tube to go from a 20" to a 16" barrel but is there anything else besides the punchs and barrel tool that I will need to make the switch. Thanks guys and im open to ideas on diff barrels that might suite me better . Im all ears!