Forster Headspace Go Gauge Belted Magnum (.535" Base) Headspace standards are set by SAAMI (Sporting Arms and Ammunition Manufacturers Institute) specific Headspace is measured from the bolt face to one of four locations, depending on the cartridge used. Headspace gages are available in three different lengths, listed below, from shortest to longest: Go Gage: Go Gages match the minimum chamber dimensions allowable under SAAMI specifications. No-Go Gage: No-Go Gages are sized to the maximum recommended headspace dimensions.