M1 No Go vs Field Gauge

I was about to order a Forester 30 Carbine Field Gauge when I read a CMP article recommending the No Go instead of the field. They also said Clymer has the proper USGI spec vs the Forester. Since I’m a M1 newbie am I misunderstanding this? Thx

Edited by kwesi1 - Oct 18 2018 at 9:19pm

We have touched on this, but I know it takes time to grasp it all. If your carbine does not close on a no-go, that’s great and indicates it has a lot of life left in it. However, the gun is safe to fire past that. If you condemned a gun based solely on the no-go measurement, you are throwing away a lot more gun. The difference between a no-go and a field is .005+-. That may not sound like much, but it’s a lot of shooting. A no-go fail indicates the gun may require service soon, but if it passed the field-gauge test, it is completely safe to fire until it fails on a field-gauge.

These gauges reflect a broad safety range. That is why I prefer to measure exactly what the head-space is. My shooting GI carbines usually measure 1.296-1.297. A no-go is 1.295 (depends on who's gauge you purchase). I am not going to start thinking about service until I see a measurement of 1.300-1.301, which is a field gauge.

floydthecat: I ordered the bolt tool you recommended. I was going to order the field gauge you also recommended instead of making the dummy round you suggested. Seemed like the easier path at the time. I sized an inverted bullet and will grab the scotch tape...thanks! Did you read my last posts on the mixed parts on my Inland 1?

Edited by kwesi1 - Oct 18 2018 at 11:55pm

Are there any reports or examples of carbine damage from firing with out of spec head space ? 

The internet is your friend for searching out such things. Most of what you’ll find are broken bolt lugs and extractors. I’m sure here in the forum, or other forums, you can find examples of such. Yours truly has cracked a bolt lug playing around with excessive head-space. Hopefully, the first thing to go would be a beat-up extractor. They will shoot loser than a 1.301 field gauge, but you’re playing with fire. Look for misfires as the firing-pin will no longer reach the primer.

I prefer the Forster Field gauge because you don't have to disassemble the bolt to use it and it's probably more accurate than making one from a carbine case. If you want to check headspace at a gun show, you can't really expect to be able to disassemble the bolt. I carry a Field gauge and a ME gauge. Usually sellers appreciate knowing that their carbine passes these checks. If the Field gauge passes then you can use the cartridge case method later to determine the actual measurement, if it really matters

In response to zenfly's question of 10/19:  "Are there any reports or examples of carbine damage from firing with out of spec headspace?”

A few years ago, my best friend had an incident with a carbine where a cartridge case separated when fired.  The results were as follows:  1. Stock split.  2.  Magazine blown apart -- the follower, spring and baseplate were blown out the bottom of the magazine.  3.  Brass from the ruptured case struck my friend in the forehead -- a small piece of brass, about the size of a BB, actually lodged just under the skin of his forehead.   

As best I remember there was no discernable damage to the receiver itself, but there may have been some damage to the lugs on the bolt.    I believe we were shooting either USGI or commercial carbine ammo (not reloads) when this incident happened. 

We had been having quite a bit of trouble with misfires (i.e., click but no bang) before the incident happened, and were observing light firing pin strikes on the primers with the misfires.  In our post incident investigation, we determined that this particular carbine was badly out of headspace – several thousandths’ beyond what is allowed by a field gauge.  We also considered slam fire as a cause, but rejected after running a few other tests and determining how badly out of headspace the carbine was.  

We now check all carbines for headspace before firing the first time, as well as check the primers on the first few rounds fired.  It doesn't take long and both are good safety measures.   Also a good reminder of why safety glasses are so important when shooting.

 

Jim B.