Excess headspace is the wiggle room from head against the breech face to as far forward as the cartridge case it can go in the chamber, whatever is stopping it. Rim for the rimmed round, shoulder for rimless bottleneck, case mouth for rimless straight wall, belt for belted magnum case, or extractor hook for when the others fail to stop forward movement in time. I like seating bullets out to headspace the bullet against the throat of the bore in the 1911.
When you get no shoulder change with TB, then gas has bled out around the case mouth before pressurizing the case enough to stretch. Increasing charge should help. Seating the bullets out to jam into the lands to raise the start pressure should help.
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Last edited by Unclenick; June 20, 2011 at 09:12 PM.