Thread: AR 10 tools
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Old September 12, 2019, 15:26   #16
hueyville
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How do you know if the upper needs to be lapped or not till do the procedure and see if it just evenly scuffs the finish or takes 0.032" off one side before lap even touches the finish on other? Have disassembled uppers with accuracy issues and discovered upper to be what I call measurably out of square just from watching it remove material from one area for a surprising amount of time before begins to make contact with rest of the face of thread face. When reassembled have had many that tightened up 1/2 to 1 MOA or more.

There are unknown variables of knowing if when assembled if barrel nut was torqued properly and I believe as important as torquing is to torque to 30/35 ft/lbs, let sit, loosen, retorque to above 40 ft/lbs then let sit several hours or overnight to loosen and do my final torque run up. Learned during engine building could torque fasteners to specs and then have them come loose due to stretching of threads and fasteners.

Have taken a very expensive hand crafted British torque wrench thats calibrated every year (like my electrical test equipment and all but my cheap lug nut torque wrenches or emergency meters that live in truck tool boxes not controlled environment) then torque a standard steel barrel nut on a $40ish Anderson/Aero/etc upper to an exact setting in one shot, let sit for a few days then put wrench back on to discover when lean on wrench nut is five ft/lbs looser than what it was torqued to due to steel nut stretching the aluminum threads. By doing three cycle run up when stop on final run can be relatively sure that it's going to stay at my "magic number" which was given to me as the preferred torque value by a smith that builds thousand dollar plus service rifle uppers every day.

ARP will not honor warranty on their Superbolts unless you send your upper in or provide documentation proving upper was squared. If barrel is canted even a hair the barrel does not line up properly with bolt carrier and bolt is always in a bind upon locking into barrel extension. Had some cerakoted uppers once where way they were hung to spray and dry every one would have an area on front of thread face the coating was significantly thicker than rest of the front like the excess was running to downhill side of face and puddling as cured.

Have had uppers so warped or with high spot not final machined properly that lap would not insert far enough to square and had to use shaft of an older lap with heavy abrasive compound and insert from front and rear till high spot was taken down or entire side of bolt run was trued. With these will see a line length of bolt run in finish that shows as shiny aluminum when finished or see a big oval "eyeball" at some area in bolt run then sometime find front was nearly perfectly in square or not. Seldom do I see an upper that is not out of square to some degree.

A lap will last most people a lifetime and is not that expensive. Takes on average an extra ten minutes to square front and clean for assembly thus I consider it a mandatory part of any build. Any torque value between 40 and 80 ft/lbs is "in spec" but I have a value almost always run up to after meticulous prep work within +/- 3 ft/lbs which get very consistent results. When run into an upper that barrels extensions are loose sit to side and use for give away builds and used/bargain barrels. Keep shim stock to snug the fit and on most uppers bed the barrel extension in the upper before final torque of barrel nut.

I only plan on assembling an upper once except for my hotrod 22 Noslers and wildcats that know will be rebarreling inside of 2,000 rounds. When going to do it once and want it to shoot as true as possible do all I can to uniform every part possible while being as consistent as possible in the assembly process. While accurate rifles can just fall together a well organized and methodical build process helps ensure utmost accuracy from all builds. This really shows on AR 10's like my pair in 6XC that in the hands of an experienced 1,000 yard shooter surprise any who let them sit in the drivers seat.

Guy who owns the private 1,000 yard range I use on occasion can shoot them into a group about four to six inches smaller than I can on average. He was stunned as did not ever consider a home built autoloader could hold a decent group at 1,000 yards but there was a stunning amount of small trueing operations to make them shoot as consistent as possible. I can shoot 16" to 18" groups with them and he was shooting groups that were averaging 14" to 16" vertically and 12" in horizontal plane. With average man being 20" shoulder to shoulder and 18" from belly button to base of neck my 18" average groups are minute of man at 1,000 yards which is good enough for me as little time as I get practicing at that distance.

AR 10's in many of the more popular benchrest cartridges are the hot ticket for fun these days and gives people who are not full bore professional machinists the opportunity to build long distance repeaters. Whether try 6XC, 6mm Credmore, 6.5 Creedmore, 260 Rem, 6.547 Lapua and others if buy a good receiver set plus a nice heavy 26" to 30" tube from reputable company then it's going to bring a lot more shooters into the long range game who don't have $7,000 to $12,000 for a well built bench rest or long range tactical rifle from a quality smith.
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