I have a DPMS upper and lower. It is a 20 in bbl (6.8 1:11)\nIts a standard A4 set up with a ACE skeleton stock on the back and a flat top upper. \n\nSince I added a KAC rail (M5 Rifle RAS PN 98065) it has become kinda front heavy with the rail set up and the heavy barrel. \n\nWhat I want to do is have it turned down and shortened to 18in. Like an SPR. How well will this work? Will the gas system work ok? Thats my biggest worry is reliability. \n\nI have looked at new barrels and It will cost as much to swap a barrel as it is to work this one down. I am looking at having http:\/\/www.ar15barrels.com do the work. \n\nPlease let me know your opinions.