From American Gunsmith:
Accuracy wise, the AR-15 has been on a roller coaster for about a half century. There are design features that make it shoot surprisingly well. However, accuracy stagnated in early life. Even when the A2 was adopted not much was done to get it shooting better. In fact, things like the burst cam, a 1:7 twist over-spinning bullets, and issue M855 ammunition with steel penetrators made it shoot worse!
In "Improving Rack-Grade AR-15s" (December 2014) I mentioned how Derrick Martin with the National Guard and I with the Army Reserve both found that 1:9 twist shoots green tip much better. I even tested 1:10 with good accuracy. We made those discoveries a quarter century ago.
When the Army Marksmanship Unit and individuals like Bill Wylde, Albert Turner, and Frank White became interested in improving ARs, several innovations took place. Float tubes removed barrel pressure, improved triggers from people like Charlie Milazzo and Bill Geissele, and true match bullets from Sierra, starting with their 69 grain MatchKing. Heavy premium barrels with an appropriate twist filled out the rest of the bill. Sierra soon released their 77 grain SMK, still magazine-length but with improved ballistic coefficient. The 80 grain SMK seated longer than magazine length but improved long range capability a bunch. Twist rates had to go back up a bit to stabilize these longer bullets and chambers were adjusted by increasing free bore. In my opinion, some of that free bore got carried away and actually compromises the performance of magazine-length ammo and the life of the barrel to this day. The rear sight improved a little as clicks were made finer and a single pin was added to the front to aid in tracking. When a second pin was added at the back, a "double pinned" rear became the new standard. The AMU took the lead along with John Holliger at White Oak. However, after that all too brief surge, the design stagnated for a period. I guess guys thought that it was as good as it was going to get.
I often compare the AR-15 to my 1966 Dodge Charger as they were born about the same time period. The Charger was equipped with a four-barrel carburetor, manual window operation, an AM-only radio, and no air conditioning. Average sticker price was around $3,100! Compare that to features common today. Automotive designers and mechanics have not been afraid to redesign and improve, nor was the auto industry afraid to risk failure. Are we collectively risking failure with firearm designs? I assure you not everything I have tried has resulted in improved accuracy. In fact, "AR-15 Build Problems" (May 2016) chronicles some of those mistrials.
During a two-decade hiatus while other gunsmiths were reluctant to innovate, I was happy to experiment for the Army Reserve. I borrowed, dusted off, perfected, polished, and sometime invented affordable, effective, and easy techniques that worked. In 2006 I also started working with bullet and barrel manufacturers to push performance further with 90 grain bullets. With Sierra's successful second generation 90 grain MatchKing my research in that arena is finished. This makes for a 90 grain long range bullet that's easy to get, to handload, totally reliable, and really bucks sudden wind changes.
Using the methods and parts detailed in this article I was able to fully cut in half the average group sizes of my Team's uppers. When I came on board only 37 out of 135 of the uppers I inherited would shoot ten-shot groups to an honest one MOA in a state-of-the-art machine rest. When I left every single upper could shoot that well. Most of this work is simple enough. As you read through the supporting articles ask, "Why didn't somebody think of this stuff forty years sooner?" If you employ the tips in this article there is no reason you can't cut your group sizes in half and achieve true sub-minute groups as well. Most of the work is easy to do, not all that time consuming, and relatively cheap.
by Joe Carlos
