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I have a question for the M14/M1A builders on here. I recently built a rifle for a friend of mine, Kreiger heavy, McMillan stock single lug Springfield receiver. The barrel was short chambered from Kreiger, I headspaced on a lathe until it was close, within a couple of thousandths. I installed the barrel on the receiver and checked headspace. The bolt would close almost all the way on a "go" gauge, bolt was within .025 of all the way closed(fully engaged on receiver lug surface). The reason I did this is I have noticed that most bolts do not bottom out in the corresponding receiver surface( correct me if I am wrong but that receiver lug surface is somewhat tapered?) On test firing with the gas system turned off I checked the fired case and the case gauge read 1.632. Am I missing something , I don't believe the receiver can stretch that much, shouldn't the fired case read 1.630. I realize it's only .002 and I have checked my case gauge with my headspace gauges and the match. Neither I nor my friend are concerned about the .002 I just like to be precise.

John
 

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Cases expand after extraction, so that is why you are seeing “growth”. Personally I headspace chambers to 1.631-1.633. Based on the description of your process I’m guessing yours is around 1.629 or so.
 

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I have a question for the M14/M1A builders on here. I recently built a rifle for a friend of mine, Kreiger heavy, McMillan stock single lug Springfield receiver. The barrel was short chambered from Kreiger, I headspaced on a lathe until it was close, within a couple of thousandths. I installed the barrel on the receiver and checked headspace. The bolt would close almost all the way on a "go" gauge, bolt was within .025 of all the way closed(fully engaged on receiver lug surface). The reason I did this is I have noticed that most bolts do not bottom out in the corresponding receiver surface( correct me if I am wrong but that receiver lug surface is somewhat tapered?) On test firing with the gas system turned off I checked the fired case and the case gauge read 1.632. Am I missing something , I don't believe the receiver can stretch that much, shouldn't the fired case read 1.630. I realize it's only .002 and I have checked my case gauge with my headspace gauges and the match. Neither I nor my friend are concerned about the .002 I just like to be precise.

John
The locking lug surfaces in the receiver are not tapered - they are helical.

Sometimes the bolt does not bottom out in the lug recess is because the bolt roller relief in the receiver is too shallow.
 

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You can get away with 1.630 and sometimes slightly less in a bolt action rifle, but not in a gas operated rifle. I've found that the best range for head space in the M14 is 1.631 to 1.634 although longer HS is generally OK. My main concern is accuracy which seems best with SAAMI specs. NATO specs run longer and HS to 1.638 is acceptable. Even chambers out to 1.640 will work OK, but barrel life will be shortened.
 

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I try to maintain 1.632 to 1.633 on all M14 rifles in my herd. Has worked out very nicely for accuracy. Agree with Ted. 1.630 might be fine for a bolt rifle but certainly not optimal for a semi auto.
 
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