I have some concern about a .300 WSM go gauge datum length.
I'm measuring with a comparator- YES, I know they are somewhat inaccurate (which is why they're called comparators)...
Normally, I don't measure the go gauges. Like reamers, I expect the geometry to be correct when buying them (most of what I have/buy is Dave Manson and don't have issues).
Just completed a build, in this case it was a lightweight hunting rifle for my son. He texted me that his fired brass datum length- with his comparator (LNL, like mine) is measuring 1.736.
I thought, crap- that's right at the edge of the SAAMI tolerance of 1.736.
I'm pretty careful about trying to get go+ .001 when chambering, especially in this case because while he handloads- he needs the ability to shoot factory in the event he travels with it and needs to buy off-the-shelf.
Measured the go gauge- and it's 1.734 to the datum on the comparator. Minimum is 1.726- waaay off. Seems our comparators must be close- as that would be .002 over "go" gauge which makes sense. What doesn't make sense to me is that this gauge appears to be ground incorrectly?
I checked several other "go" gauges- .284 Win (same .420 datum) and some smaller .400 datums (.308, 6.5 Creed) and they all measured at or below minimum SAAMI spec. So again, I know the comparator isn't precise- but the "comparative" measurements of the gauges are leading me to believe this gauge may be defective.
So, I have two questions:
First, SAAMI specs a min/max length to the datum, usually about .010 tolerance between them. I'm "assuming", minimum is what the go gauge should measure- with some tolerance to be longer- what is acceptable?
I'm only concerned in this case, because it appears we are very close to "no go" headspace. The new Norma brass is 1.728-1.730 on his comparator- so we're stretching this .006 -.008 thou. If he got a box of factory ammo on the small side, there would be a hell of a lot of stretching going on.
Obviously- can't risk a case head separation.
He can size/bump accordingly down to 1.734-1.735 so as not to overwork the brass- but is my concern about (apparently) being so close to the upper bound legit?
I'm measuring with a comparator- YES, I know they are somewhat inaccurate (which is why they're called comparators)...
Normally, I don't measure the go gauges. Like reamers, I expect the geometry to be correct when buying them (most of what I have/buy is Dave Manson and don't have issues).
Just completed a build, in this case it was a lightweight hunting rifle for my son. He texted me that his fired brass datum length- with his comparator (LNL, like mine) is measuring 1.736.
I thought, crap- that's right at the edge of the SAAMI tolerance of 1.736.
I'm pretty careful about trying to get go+ .001 when chambering, especially in this case because while he handloads- he needs the ability to shoot factory in the event he travels with it and needs to buy off-the-shelf.
Measured the go gauge- and it's 1.734 to the datum on the comparator. Minimum is 1.726- waaay off. Seems our comparators must be close- as that would be .002 over "go" gauge which makes sense. What doesn't make sense to me is that this gauge appears to be ground incorrectly?
I checked several other "go" gauges- .284 Win (same .420 datum) and some smaller .400 datums (.308, 6.5 Creed) and they all measured at or below minimum SAAMI spec. So again, I know the comparator isn't precise- but the "comparative" measurements of the gauges are leading me to believe this gauge may be defective.
So, I have two questions:
First, SAAMI specs a min/max length to the datum, usually about .010 tolerance between them. I'm "assuming", minimum is what the go gauge should measure- with some tolerance to be longer- what is acceptable?
I'm only concerned in this case, because it appears we are very close to "no go" headspace. The new Norma brass is 1.728-1.730 on his comparator- so we're stretching this .006 -.008 thou. If he got a box of factory ammo on the small side, there would be a hell of a lot of stretching going on.
Obviously- can't risk a case head separation.
He can size/bump accordingly down to 1.734-1.735 so as not to overwork the brass- but is my concern about (apparently) being so close to the upper bound legit?
