WE'VE BEEN BUILDING CUSTOM AR' UPPERS FOR QUITE SOME TIME. WE'VE USED THE FOLLOWING BARRELS IN THESE BUILDS:
COLT
LMT
KRIEGER, BY COMPASS LAKE ENGINEERING
DOUGLAS, BY COMPASS LAKE ENGINEERING
LILJA, BY COMPASS LAKE ENGINEERING
NOVESKE S/S
NOVESKE N4
OUR PREFERRED BOLTS ARE THE PROOF-ROUND TESTED, MP-INSPECTED VARIETY FROM LMT. WE TRY TO KEEP QUITE A FEW ON HAND. THEIR TOLERANCES ARE QUITE GOOD, SPANNING A MAX RANGE OF 0.004", WITH 90+% OF THEM WITHIN 0.003" AND 70% WITHIN 0.002".
WE HAVE TWO COMPLETE SET OF PACIFIC TOOL AND GUAGE HEADSPACE GAUGES FROM 1.4626" TO 1.4716" IN INCREMENTS OF 0.001". THIS MAKES PRECISE FITTING OF A BOLT TO A BARREL FOR A GIVEN APPLICATION POSSIBLE. (BUT TEDIOUS!)
WE TYPICALLY SET UP A GENERAL USE GUN WITH A HEADSPACE OF 1.4666". I MIGHT GO LOOSER ON A GUN I KNOW IS GOING TO BE RUN HARD ON GENERIC BALL AMMO, SAY LIKE A 10.5" N4 GOING TO A SWAT TEAM MEMBER OR CIVILIAN HEADED FOR A 5-DAY TRAINING CLASS. PRECISION RIGS I LIKE TO RUN A TAD ON THE TIGHT SIDE IF I KNOW MATCH GRADE AMMO WILL ONLY BE USED.
COMPASS LAKE MATCH CHAMBERS RUN TIGHT. I HAVE RUN INTO SOME THAT WOULD BE COMPATIBLE WITH EACH AND EVERY BOLT I HAD. SO, THESE GOT LMT BOLTS FROM ONE END OF THE SPECTRUM IN ORDER TO MEET MINIMUM CHAMBER DIMENSIONS.
NOVESKE SPEARS ALL OF HIS CHAMBERS AT 1.4666" BY DESIGN. FOR A PRECISION BUILD FOR USE WITH MATCH GRADE AMMO AND ONE OF HIS S/S BARRELS, I'LL LOOK FOR A BOLT THAT WILL CLOSE AT 1.4646" - 1.4656".
DOES THESE THEORIES WORK? BASED ON RESULTS, I LIKE TO THINK SO. CAN I PROVE IT SCIENTIFICALLY? OF COURSE NOT.
GOOD SHOOTING,
WES