My M91/30 Mosin seems to not be cooperating with headspace gauges


I finally acquired headspace gauges (Firewerks), all three, but strangely none of the three let the bolt close–including the “Go” gauge. I test chambered a live round and everything is perfect and butter smooth.



Take a picture of them and the package they came in. Could the extractor be getting in the way of the gauge seating flush agents the face of the bolt? If memory serves the head space gauge for that cartridge should be short compared to a cartridge style head space gauge.


The Firewerks gauges are in the below link. You don’t need to remove the extractor like you do with the other gauges. These are like the Okie gauges, in fact are copies of them. Hah.

You’ll see the headspace gauge in this picture below.


Yeah James, everything looks good in the pictures, I’m guessing that there is no grease, debris, or abstraction on the face of the bolt or the breach of the chamber? The gauges are cheap, but look like they should work.
Is the bolt a match to the action? Do they have the same serial number?

P.S. check your gauges.
Field gauge 0.076"
NoGo gauge 0.073"
Go gauge 0.064"
Gauge diameter 0.562"
Firing pin clearance 11/64"
Extractor notch 1/4" x 0.180"
Hold all tolerance to 0.0005”


I haven’t done a good clean on it yet but it does at least look clean enough for this purpose. It is all numbers matching as well. I don’t have a measuring tool, so what tool do I need to get to measure these that’s inexpensive? I’m going to clean this rifle up and try again. Since it chambered a live round that’s what had me puzzled.


A simple dial caliper should do fine. The rifle is most likely fine, but it’s always safer to double check

I would be far more concerned if the action closed on all 3 gauges.


Perfect, thanks. I’ll get one of those off of Amazon. I absolutely want to double check since this is my wife’s Mosin. Had a gunsmith check mine but now I’m curious to see if these gauges work properly on mine.

I wonder if the arsenal refurbishing has something to do with this issue? Because I’ve got an arsenal refurb mark on the stock.


That is entirely possible. Does the rifling go all the way to the end of the muzzle? If it stops short by an inch or two it has definitely been done.


The good news is all rifling is crisp and through the length of the barrel. Surprisingly the barrel is near mint. It has not been counterbored. The bad news is I think it’s got some cosmoline in the chamber so that likely might be the culprit. I’m going to clean it and try again at a later time.

FYI the headspace gauges work flawlessly with my former PU sniper so it appears to definitely be an issue with either a dirty chamber and or VERY tight tolerances on my wife’s Mosin?


That’s all good news! Hit the wife’s action area with a hair dryer “ out doors for your sake ” on the chamber and that will aid in the removal of the cosmoline.


Good idea! I was going to use the trash bag + newspaper trick out in the car’s trunk in the hot Texas sun. :slight_smile: