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Old November 26, 2012, 03:05 PM   #32
Bart B.
Senior Member
Join Date: February 15, 2009
Posts: 6,318
JRLSH, your original:
OK guys, then I have a question concerning headspace. I am reloading for a .50BMG and recently purchased a Lyman headspace gauge. Some of my cases are spot on between the minimum and maximum on the gauge but some of my cases are up to .010 shorter than the minimum on the gauge. When loading for a caliber this large I would think this is a large problem but in doing research some say that this measurement is within acceptable ranges, but is that a measurement that will lead to case head separation upon firing in my bolt gun? I have not shot any cases yet and have only reloaded the cases that were completely spot on. AND some of the cases that are short on headspace dimentions are all spot on for OAL after trimming. Any help on this?
Are you using the distance from the BMG round's case head to the mouth as headspace?

If so, that's not what headspace gauges for 50 BMG chambers are set up to measure. They measure the distance between the bolt face and some reference on the chamber shoulder that's at a 15 degree 44 minute angle. I've not found anyplace that states what headspace should be relative to that. It's somewhere between 3.0056" and 3.2790". For a reference diameter of .6600" on the shoulder, it's about 3.1000" as I calculate from available dimensions on this drawing:

Contact Manson Reamers at:

then ask them what the GO and NO-GO headspace dimensions are for the 50 BMG round. They make those gauges so they have to know.
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