Cartridge size vs. SAAMI chambers

[Smokey262]

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?

[Captain Finlander]

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.

[bigedp51]

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/o254/bigedp51/IMGP7211.jpg

http://i122.photobucket.com/albums/o254/bigedp51/IMGP7212.jpg

The .243 case below is .006 under or 1.624

http://i122.photobucket.com/albums/o254/bigedp51/IMGP7214.jpg

The Forister .308 Match Rifle Headspace Gauge Kit below are in .001 increments starting at 1.630

http://i122.photobucket.com/albums/o254/bigedp51/308-762gaugesjpg.jpg

http://i122.photobucket.com/albums/o254/bigedp51/243jpg.jpg