I am reducing the headspace in my 2012 M305 by replacing the bolt with another used Norinco bolt.
New used bolt would not close on Manson .308 nogo gauge. New used bolt does close on Manson .308 go gauge.
Very good so far.
I have an RBCS brass measuring mic. I put the Manson gauges in the mic and observed that the go mics at 1.6300, the nogo at 1.6348 and the field at 1.6382 . No problems here.
I then fired 5 rounds of Federal blue box 150 grain with the gas system turned off. All 5 empty casings measured 1.6300. I then fired 5 rounds of the same ammo with the gas system turned on. All 5 casings measured 1.6340.
Unfired Federal rounds out of the box all measured 1.626 to 1.628, average was 1.6272.
I was surprised that having the gas system on could have such a large effect on measured brass. Anyone else see this? I am inferring that the head space is about 1.632. ( measured cases with gas system off plus assumed shrinkage of .002). Appreciate your comments. Thanks.
New used bolt would not close on Manson .308 nogo gauge. New used bolt does close on Manson .308 go gauge.
Very good so far.
I have an RBCS brass measuring mic. I put the Manson gauges in the mic and observed that the go mics at 1.6300, the nogo at 1.6348 and the field at 1.6382 . No problems here.
I then fired 5 rounds of Federal blue box 150 grain with the gas system turned off. All 5 empty casings measured 1.6300. I then fired 5 rounds of the same ammo with the gas system turned on. All 5 casings measured 1.6340.
Unfired Federal rounds out of the box all measured 1.626 to 1.628, average was 1.6272.
I was surprised that having the gas system on could have such a large effect on measured brass. Anyone else see this? I am inferring that the head space is about 1.632. ( measured cases with gas system off plus assumed shrinkage of .002). Appreciate your comments. Thanks.
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