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For a 243 Winchester my understanding is that the SAAMI cartridge size spec is 1.627"-1.634", and the chamber size spec is 1.630"-1.640".
My Forster headspace go gauge is marked 1.630", yet measures 1.622" to the 0.400" datum
A new factory Federal cartridge measures 1.622" to the datum
Why the disparity? How would a max spec cartridge fit into a min spec chamber? Why does the go gauge measure less than what it is stamped, and it is less than the min chamber spec?
The short answer, use more muscle to close the bolt. ;D
Can the gauge and take a casting of your chamber. It will be more accurate.
I would think the Forster headspace gauge is the correct length of 1.630 and what you are using to measure the gauge is off or giving false readings. A Forister GO headspace gauge .008 undersize is not a very high possibility.
http://i122.photobucket.com/albums/o...1/IMGP7211.jpg
http://i122.photobucket.com/albums/o...1/IMGP7212.jpg
The .243 case below is .006 under or 1.624
http://i122.photobucket.com/albums/o...1/IMGP7214.jpg
The Forister .308 Match Rifle Headspace Gauge Kit below are in .001 increments starting at 1.630
[img width=450 height=450]http://i122.photobucket.com/albums/o254/bigedp51/308-762gaugesjpg.jpg[/img]
[img width=347 height=450]http://i122.photobucket.com/albums/o254/bigedp51/243jpg.jpg[/img]