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Discussion Starter #1 (Edited)
In a prior topic, it was posted that building an AR without checking head-space was inviting disaster. I have heard the other side of the coin many times that it wasn't necessary because components are built to specifications with tight tolerances. I share the later view and have shot rifles (not ARs) with significant headspace issues which only resulted in split brass. Regardless of your view point, I thought of a way to check my new-build AR's headspace with no tools. When my BCG came in today, I took the BCG apart. I placed a new piece of brass with a flush primer installed into the chamber, and inserted the bolt (don't use a case loaded with powder and a bullet to do this - only a primer). That told me I had enough headspace especially since I could do it by hand. Then I used the firing pin to measure the freeplay/headspace tolerance of the chamber by sliding the firing pin into the back of the bolt and letting it touch the brass. The plunger forces the brass forward into the shoulder leaving any freeplay at the bolt's face. The difference between the firing pin flush with the bolt face and with the brass in the chamber is your freeplay. You can actually see the difference in the gap between the flat on the ring stop of the firing pin and the back of the bolt. If there is no gap, you have too much headspace.
 

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I suppose that will work. The issue with AR's (and most semi-auto firearms) is they tend to have large (long) chambers to ensure reliable feeding. You can take a no-go gauge and stick it in most any 5.56 chamber and with just a little force push the bolt closed. Same with an M1A or a M1. I've sat in Gene Barnett's shop in Tennessee and watched him finish ream M1A and M16 Designated Marksman Rifle barrels he was building for the 101st Airborne and the Navy and the bolts on all those guns would close on a no-go gauge. The military standard on these guns is a "Field gauge" which is larger than a no-go gauge.

In terms of building a rifle and checking headspace. I have the gauges for 5.56 but I've built a dozen 5.56 guns for myself and a few other people. But with the two 6.8's I built I simply put it together, took it to the range and fired a few factory rounds holding the gun at arms distance making sure to wear safety glasses and gloves. I then took the fired casings and measured them in my Wilson Case Gauge. The fired cases should fit in the gauge and not stick out of the back (within reason).

FWIW, I check all my serious hunting and competition reloaded ammo with a case gauge. Its too easy and simple NOT to do it and can save you a deer/elk or points in a match. Dillon makes case gauges for the more common calibers that are less than $20 and Wilson makes them for calibers like the 6.8 SPC

YMMV
 

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Good post; however, since I also agree that the best cure for worrying about headspace, using new, quality components is Paxil, I'll continue to just put 'em together and keep on shootin'!
 

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Discussion Starter #4
the bolts on ... those guns would close on a no-go gauge. The military standard on these guns is a "Field gauge" which is larger than a no-go gauge.
KJ, I read in Shooting Times a couple of months ago about headspace. It too stated that you bolt can close on a no-go gauge and still have a good chamber. The important parts of this check would be that you can close the bolt by hand and that there is enough space between the back of the bolt and the flat stop on the firing pin to initiate the primer. Mine was around 0.025 which should be good. Again, don't use a case loaded with powder and a bullet to do this.

UsingBolttoCheckHeadspace.jpg
 

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One thing... Few primers actually seat flush with the back of the case. Most sit a few thou below. So you have to take into account the fact that your aren't measuring true headspace by just measuring the firing pin.
 
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