02-16-2020, 02:17 PM
One thing I failed to mention is how accurate are our calipers. I suspect my calipers are good to within .002 maybe a little less accurate (or how repeatable). You throw in all the variables and you see how tolerances can stack and create issues. It just bugs me a manufacturer would continue to manufacture a 2.800 inch long 6.5 Grendel bolt.
Odin Works was the first to experience pierced primers which was traced to excessive FP penetration and 2.800 length bolts. The first Toolcraft 6.5 Grendel bolts were 2.800 but they quickly changed to 2.8100 length. There were one or two other companies that had an initial run of 2.800 length 6.5 Grendel bolts but switched to 2.810 length bolts.
Like I mentioned in my previous post. Your Brownell’s BCG is very close and the only way I’d know for sure is to check the protrusion with a gauge. When I figured your BCG might be .002 long I was using the figure of 3.279 for firing pin length. The specification for FP length is vague but lets say spec is 3.279 +or- .001. A FP length of 3.280 like one of mine might pass. To many variables in the thousandths of an inch to know for sure.
In all my research most sources indicate AR-15 firing pin length is 3.279. One source listed FP length of 3.279 with a tolerance of -.009. Other sources listed different FP lengths + or - .001. Most sources refer to bolt length, bolt face depth and FP protrusion more than FP length. There doesn’t appear to be an accepted manufacturing tolerance for bolt FP as long as protrusion is in spec. With mass produced products it kind of makes sense to use the FP protrusion to account for variations in the manufacturing process.
Odin Works was the first to experience pierced primers which was traced to excessive FP penetration and 2.800 length bolts. The first Toolcraft 6.5 Grendel bolts were 2.800 but they quickly changed to 2.8100 length. There were one or two other companies that had an initial run of 2.800 length 6.5 Grendel bolts but switched to 2.810 length bolts.
Like I mentioned in my previous post. Your Brownell’s BCG is very close and the only way I’d know for sure is to check the protrusion with a gauge. When I figured your BCG might be .002 long I was using the figure of 3.279 for firing pin length. The specification for FP length is vague but lets say spec is 3.279 +or- .001. A FP length of 3.280 like one of mine might pass. To many variables in the thousandths of an inch to know for sure.
In all my research most sources indicate AR-15 firing pin length is 3.279. One source listed FP length of 3.279 with a tolerance of -.009. Other sources listed different FP lengths + or - .001. Most sources refer to bolt length, bolt face depth and FP protrusion more than FP length. There doesn’t appear to be an accepted manufacturing tolerance for bolt FP as long as protrusion is in spec. With mass produced products it kind of makes sense to use the FP protrusion to account for variations in the manufacturing process.