I randomly performed some quick concentricity tests on all the different brands if .308 brass I had, and at the top of the concentricity list was LC LR I observed only a .001" TIR . My special .300 Win Mag W-W millspec marksman brass was also very tight with about a .0015" TIR. R-P commercial brass also ranked high but not as good as LC LR, and the W-W. PPU , PMC , FC and standard LC brass all measured about .0025" - .0035" .
Rubber O ring decreases runout? Basic die and theory question. Gauge suggestion?
- Thread starter Danattherock
- Start date
On the concentricity gauge, here is what to make sure the tool does NOT do:
It should not support the case at the bottom of the extractor groove.
It should not support the case at the shoulder/neck junction
It should not turn on a painted surface
Some concentricity gauges do this because it is simpler to make so that the bullet will not slide down hill.
My home made rig is just four 1/4" pins that have rounded/polished tips. Two pins near the base, two pins near the shoulder, and a fifth pin at the back as a register, all drilled into a piece of scrap maple. The indicator mounts on an articulated arm stolen from a magnetic indicator base. Took me all of an hour to make, it only works for .308 sized cartridges. The thing to remember is that it only needs to measure the relative variation between the body to neck, and the body to projectile. It does not need to measure absolute variation between any part of the bullet and the base/ground/moon/etc, so it does not matter if the board changes dimensionally a bit from day to day. It does not matter if the pins have a few thousand variation in height. All that matter is that the case is well supported, and turns very smoothly. It will give the same relative variation on each use. We have other tools for measuring absolute variation.
This is possibly the simplest tool we use, and requires the least amount of precision in manufacture to get very accurate results. Even cheap Lee dies require more precision in manufacture. The cost of these things is way over the top.
-Josh
It should not support the case at the bottom of the extractor groove.
It should not support the case at the shoulder/neck junction
It should not turn on a painted surface
Some concentricity gauges do this because it is simpler to make so that the bullet will not slide down hill.
My home made rig is just four 1/4" pins that have rounded/polished tips. Two pins near the base, two pins near the shoulder, and a fifth pin at the back as a register, all drilled into a piece of scrap maple. The indicator mounts on an articulated arm stolen from a magnetic indicator base. Took me all of an hour to make, it only works for .308 sized cartridges. The thing to remember is that it only needs to measure the relative variation between the body to neck, and the body to projectile. It does not need to measure absolute variation between any part of the bullet and the base/ground/moon/etc, so it does not matter if the board changes dimensionally a bit from day to day. It does not matter if the pins have a few thousand variation in height. All that matter is that the case is well supported, and turns very smoothly. It will give the same relative variation on each use. We have other tools for measuring absolute variation.
This is possibly the simplest tool we use, and requires the least amount of precision in manufacture to get very accurate results. Even cheap Lee dies require more precision in manufacture. The cost of these things is way over the top.
-Josh
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