FN Mauser Headspace Check

[FAL]

I just got an FN Mauser in .308. I checked the headspace with my Forster GO and NO-GO gauges and both fit. Should I try a field gauge?

What if it fits? Gunsmith time?
What if it doesn't fit? Is everything OK then?

Is there anything unique to these rifles when it comes to headspace?

Thanks,

Dave

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[dobeman]

nope. If you passed the no-go gauge, ie., you couldn't close the bolt on the no-go gauge. No need to try a field gauge (worse case). Now, if you mean fit as in the bolt closed completely on the no-go gauge, then you need to try a field gauge. It should not close on the field gauge.

 

[FAL]

nope. If you passed the no-go gauge, ie., you couldn't close the bolt on the no-go gauge. No need to try a field gauge (worse case). Now, if you mean fit as in the bolt closed completely on the no-go gauge, then you need to try a field gauge. It should not close on the field gauge.

Yes, it closed completely on the no-go gauge.

So I have ordered a field gage.

My questions are (1) if it does not close on the field gauge, is the gun OK to fire despite the fact it closed on the no-go gauge? (2) If it closes on the field gauge, it must go to the gunsmith, correct? Is there anything a non-gunsmith can do to correct it?

 

[dobeman]

FAL, correct. That is my understanding on the use of the gauges. If it closes on the Field gauge, there is too much headspace. If it does not close on the field gauge, then should be safe to shoot. As to what is done if fails field gauge, i do not know. I'd like to know the answer myself just in general as I dabble more and more into milsurp rifles.

 

[bumpkin]

I have heard that there are differences between .308 and 7.62 chambers. There is some info in this .PDF file from Forster:

<broken link removed>

 

[MountainBear]

Sorry, its gunsmith time. If it closes on a no-go gage, then you have excessive headspace. The barrel needs to be removed and the barrel needs to be set back.

You might be able to get away with it if it doesn't close on a field gauge, but that's worse case already. It needs to be fixed...

 

[Blitzkrieg]

Mountain bear is right

BTW some Mausers were re barreled with Israeli heavy stepped military barrels that are 7.62 NATO chambered .. so be sure what barrel/chambering you have. From Bumpkin's link:

Although all other case dimensions of the two cartridge cases remain the same, one important difference
exists: the 7.62 NATO chambering has a longer headspace dimension than the commercial
.308 chambering. Hence, the need for rifle chamber Headspace Gages specifically designed and
manufactured to check the slightly longer 7.62 NATO chambers.

This could explain the no go closing in the action, if you have the 7.62 chambering. If you have a commercial FN .308 then do not fire the gun

 

[FAL]

Mountain bear is right

BTW some Mausers were re barreled with Israeli heavy stepped military barrels that are 7.62 NATO chambered .. so be sure what barrel/chambering you have.

OK I'm impressed, this is exactly what I have, an Israeli heavy stepped military barrel. The barrel is machine marked "7.62" but it is also hand stamped ".308 Win". My GO gauge is a Forster HG0243G and the NO-GO is a Forster HG0243N, both are for 243 Winchester, 260 Remington, 7mm-08 Remington, 308 Winchester, 338 Federal, 358 Winchester.

So are we saying that 7.62 is a little longer and that I should get a 7.62 headspace gauge set? And if the GO goes and the NO-GO doesn't to just use 7.62 ammo in it?

 

[FAL]

OK, .308 Field and 7.62 NATO NO-GO gauges ordered....
We'll see what they report....

 

[FAL]

Here's some good reading on the topic:

http://www.303british.com/id36.html

 

[FAL]

Here are the barrel stamps:

View attachment 208935

 

[Blitzkrieg]

OK I'm impressed, this is exactly what I have, an Israeli heavy stepped military barrel. The barrel is machine marked "7.62" but it is also hand stamped ".308 Win". My GO gauge is a Forster HG0243G and the NO-GO is a Forster HG0243N, both are for 243 Winchester, 260 Remington, 7mm-08 Remington, 308 Winchester, 338 Federal, 358 Winchester.

So are we saying that 7.62 is a little longer and that I should get a 7.62 headspace gauge set? And if the GO goes and the NO-GO doesn't to just use 7.62 ammo in it?

Yes

 

[MountainBear]

There are certain times when kitchen table gunsmithing is a good idea. Things like headspace are not one of those times. It might be a time when having the chamber cast would be a good idea to make sure someone didn't blow out the chamber to a wildcat.

 

[Blitzkrieg]

There are certain times when kitchen table gunsmithing is a good idea. Things like headspace are not one of those times. It might be a time when having the chamber cast would be a good idea to make sure someone didn't blow out the chamber to a wildcat.

It's cheap and a good idea

 

[FAL]

It's cheap and a good idea

Already the gun is technically disqualified for .308 - but MIGHT be OK if the field gauge doesn't fit. And if the 7.62 NATO NO-GO doesn't fit, I'm seriously considering removing the ".308 Win" from the barrel and making it obvious that its a 7.62 NATO only rifle.

But casting is a great idea!!

 

[Blitzkrieg]

Already the gun is technically disqualified for .308 - but MIGHT be OK if the field gauge doesn't fit. And if the 7.62 NATO NO-GO doesn't fit, I'm seriously considering removing the ".308 Win" from the barrel and making it obvious that its a 7.62 NATO only rifle.

But casting is a great idea!!

Seems to me someone with very limited understanding of the calibers stamped that ".308" on your barrel. The izzy stepped barrel does not have that stamping

 

[FAL]

Seems to me someone with very limited understanding of the calibers stamped that ".308" on your barrel. The izzy stepped barrel does not have that stamping

The stamping is definitely an afterthought..

But I got my .308 field gauge. The bolt closes about 3/4 of the way on it but does NOT close all of the way. Can we draw any conclusions yet or shall we wait for the 7.62 NATO NO-GO gauge?

 

[Blitzkrieg]

The stamping is definitely an afterthought..

But I got my .308 field gauge. The bolt closes about 3/4 of the way on it but does NOT close all of the way. Can we draw any conclusions yet or shall we wait for the 7.62 NATO NO-GO gauge?

Since it's 7.62 I would wait for the gauge..

 

[vern357]

Honestly, if it is checking out ok with the field guage, you should be OK. Wait for the other one if you like, but keep in mind that the go and no-go guages are for a new gun right out of the factory, but the field guage is for a used gun.

 

[MountainBear]

Honestly, if it is checking out ok with the field guage, you should be OK. Wait for the other one if you like, but keep in mind that the go and no-go guages are for a new gun right out of the factory, but the field guage is for a used gun.

Umm, no. The field guage was used as a MAXIMUM safe headspace for military rifles (I know this is a mil-surp, but still). Use a go and no go, especially if you are a reloader. Since it did not close on a field gauge, its probably not going to blow up on you, but it will be spiking pressure a bit (I take no responsibility for this, notice the PROBABLY). It will also be stretching the brass quite a bit in the web and will shorten the brass life for reloading. The rifle will probably not be living up to its accuracy potential as there is more than likely a large jump from case mouth to the start of the rifling.

Wait for the 7.62 gauges. Check the go and no-go. If it passes, then I might have the chamber cast to make sure, but it should be good to go with 7.62 ammo. If it fails, then the gun's barrel needs to be set back. If it were my gun, that would be the way I'd go. Headspace is not a game of okay or good enough. It needs to be right.