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Posted: 4/1/2017 11:25:30 PM EDT
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Got a well used Vietnam bringback Mas 36 about 8 or 9 years ago and never shot it due to hard to find ammo.
Finally picked up 2 boxes of Prvi ammo and noticed that the firing pin hole was eroded badly and ordered a replacement bolt. The bolt fit and I got it headspace checked. It closed easily on a NO-GO and just BARELY stopped before fully locked on the FIELD gauge. 
Even tried a couple other bolts, and they closed completely on the Field gauge, so the first replacement was the "best". Is it worth firing, or just leave it as-is as a wall hanger? |
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Quoted:
You should sell your rifle to someone who collects and appreciates Vietnam bringbacks. You will likely receive more than enough to purchase a much nicer shooter grade MAS 36. I never planned to shoot this one until I saw the local gun shop had a few boxes of 7.5 French on the shelf. I would honestly like to find a pre-war Mas 36 though. |
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If you look at a SAAMI cartridge and chamber drawing headspace is listed as min and max with .010 in between the two. A GO and NO-GO are used for setting headspace on a new rifle and has .003 in between the two. And a Field Gauge is .010 longer than the GO gauge.
A British .303 Enfield rifle at maximum military headspace of .074 with a case with a rim thickness of .058 will have .016 head clearance. Meaning .016 "air space" between the rear of the case and the bolt face. 
The amount of head clearance is the distance the base of the case will stretch and thin when fired to contact the bolt face. Your shoulder bump on a resized case is the head clearance when the cartridge is chambered. This is why it is recommended to have .001 to .002 shoulder bump for a bolt action rifle. The .001 to .002 is within the brass elastic limits and for the brass to stretch and spring back without stretching and thinning. I have old British .303 Enfield rifles that are well over maximum military headspace that have matching numbers. I do not replace the bolt or change bolt heads, I simply fire form the cases for that chamber and let these cases headspace off the shoulder and not the rim. 
When shooting rifles with excess headspace you simply measure expansion above the rim or extractor groove. Normally this is the unsupported part of the case "outside" of the chamber and you measuring how much the case expands. If the case expands .0005 to .001 in this area your chamber pressure is too high, meaning your loads might be at the recommended start load to be safe. You can also load cast bullets with reduced loads for these old tired well used rifles. Below I'm fire forming .303 cases with reduced loads and .312 pistol bullets. This also makes the brass butt plate "softer" when forming 100 to .200 cases. 
Below a rubber o-ring is slipped over the case to hold it against the bolt face. When the o-ring is compressed it centers the case in the rear of the chamber and makes more concentric ammo. 
Bottom line excess headspace is not the end of the world if you want to keep shooting these old war horses. And all you need to do is keep an eye on your cases and use common sense about your chamber pressure. I have fired Enfield rifles that were .010 over maximum headspace with factory ammunition without any problems. You wouldn't want to reload a case like this because of stretching and thinning in the base of the case. "BUT" if the o-ring method is used the case does not stretch and thin and can be reloaded many times. |
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