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Some info on Headspace of Navy Garands that CMP is selling

This is a discussion on Some info on Headspace of Navy Garands that CMP is selling within the Gus Fisher forums, part of the Gun Professionals category; First, allow me to say there were TWO distinctly different Headspace Chamberings for Navy M1 Garands. The ones they did the LEAST AMOUNT OF were ...


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Old November 14th, 2012, 07:55 AM   #1
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Some info on Headspace of Navy Garands that CMP is selling

First, allow me to say there were TWO distinctly different Headspace Chamberings for Navy M1 Garands. The ones they did the LEAST AMOUNT OF were for the Navy Rifle Teams and only SOME of their Marksmanship Award Rifles, these were chambered to shoot .308 win as well as 7.62mm. The OVERWHELMING MAJORITY of Navy Garands were chambered for the 7.62mm cartridge and even some of the "lower grade" Award Rifles they gave out for winning some marksmanship competition.

Cmdr. Jim Adell,USN retired, and THE recognized authority on Navy Garands separated and pulled the rifles by serial number that had belonged to or made for the Navy Marksmanship Programs. The intention was that former and current Navy shooters will be able to get "one of their rifles." I think that's great, BTW. SO........... what that means is that MOST of the Navy Garands CMP is selling are those Standard ones that were chambered for 7.62mm.

We had 3,000 7.62mm Navy Garands at Quantico that we got from the Navy for issue to Marines as Award Rifles. I headspace checked well over 1,000, if not 2,000 or more of them over the years. These were all STANDARD Navy 7.62mm Garands and NOT the ones built by the Navy Teams or Navy programs for their NM Rifles.

STANDARD Navy Garands were chambered for 7.62mm and NOT .308 Win. as I mentioned. You will often find the Headspace in these rifles to be long to too long for any but the best .308 cartridge brass and should stick to quality 7.62mm military brass if your headspace is too long for .308 win.

What I and others who have inspected MANY of these rifles have found can be upsetting for some folks, so let me go over that first. I RARELY ever found a STANDARD 7.62mm Navy Garand that would not close on a 1.634" .308 Win. NO GO gage AS IT CAME FROM THE NAVY MODIFICATION PROGRAM and Arsenals. (I am NOT referring to the guns built for the Navy Marksmanship programs as they were normally built with tighter headspace.) The NO GO gage is NOT the maximum safe headspace, though. If the bolt closes on this gage, it still MAY be good to shoot both .308 win and 7.62mm DEPENDING on what the longer Headspace Gages show. The REASON for this is the 7.62mm GO gage is less than Half a Ten Thousandth of an Inch shorter than the 1.634" .308 Win NO GO gage. So, if the bolt closes on a 1.634" .308 Win NO GO gage, don't freak out yet!!

The next HS Gage you MUST HAVE is the 1.638" .308 Win. FIELD REJECT Gage. This gage DOES give you the maximum length of safe headspace for .308 Win by SAAMI standards. Please carefully read Items 1. through 3. that follow.

1. If the bolt does NOT close on a 1.638" .308 Win. FIELD REJECT Gage, then you CAN shoot both .308 Win and 7.52mm out of it.

2. IF the bare bolt closes on a 1.638" .308 Win. FIELD REJECT Gage, with no more friction than without the gage, you have gone BEYOND Safe Headspace Maximum for the .308 Win. as SAAMI has specified. ALSO, you need to check with a THIRD HS gage to ensure the rifle is safe to shoot.

3. To ensure the rifle is safe to shoot when it closes on the 1.638" .308 Win. FIELD REJECT Gage, you MUST check it with the GI Spec Field Reject Gage that is 1.6445" long. If the bolt does NOT CLOSE on this gage, it is still safe to shoot with SOME kinds of ammo. Unfortunately, it is not easy to find GI Field Reject Gages. If you can find a commercial Field Reject gage that is 1.640" in length and the bolt does not close on it, you are good to go with SOME kinds of ammo.

HOWEVER, DO NOT SHOOT JUST ANY OLD .308 Win ammo in it. You MUST have ammo with cartridge cases thar are as tough as 7.62mm cases. TRUE GI 7.62mm NATO ammo with the "cross n the circle" on the headstamp and in good condition is good as are many foreign makers of QUALITY 7.62mm Nato ammo (with the Cross in the circle stamped on it that means it is NATO spec.) NOT all commercial .308 Win ammo is made that way, though. Federal Gold Medal Match .308 Win ammo is known for having tough enough brass and Federal American Eagle most likely is as well. Winchester "White Box" 7.62mm ammo is also good to use and some other of their ammo will work, but you should contact them if you have a question. This is the WRA ammo I'm talking about in the link below:

http://www.midwayusa.com/product/290...l-metal-jacket

For the actual Headspace Gage dimensions for each caliber, please see Post Number 3. For more information on Headspace Gages, please see Post Number 7 in this thread:

A little bit of everything to do with headspace.

Thanks from Rifleman, liftrat22, honer and 8 others

Last edited by Gus Fisher; November 15th, 2012 at 06:55 AM.
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Old December 3rd, 2012, 03:45 PM   #2
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Gus,

Awesome information. Thanks for taking the time to post this, as well as your other thread on headspacing. I've bookmarked them both for future reference.

I just bought one of those CMP Navy Garand B/R's. This thing is in beautiful shape. Looks hardly used. I got a 12 series SA bolt for it, new-old stock.

Anyways, I got a Forster 7.62 Max 1.6455 gauge (I know how you feel about Forsters...but I had already ordered the damn thing before I read your other thread) and it would NOT close on the max gauge.

Should I still go ahead and get a set of Clymer's and run the headspace again or do you think it'll fire okay?

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Old December 3rd, 2012, 04:12 PM   #3
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Gus,

Thanks for the info! I'm using a NOS SA bolt, which used with this USN barreled receiver from the CMP closes on a 7.62 MIN gauge, and will not close on a 7.62 MAX or a .308 Field gauge.

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Old December 3rd, 2012, 06:02 PM   #4
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Quote:
Originally Posted by Cavtanker View Post
Gus,

Awesome information. Thanks for taking the time to post this, as well as your other thread on headspacing. I've bookmarked them both for future reference.

I just bought one of those CMP Navy Garand B/R's. This thing is in beautiful shape. Looks hardly used. I got a 12 series SA bolt for it, new-old stock.

Anyways, I got a Forster 7.62 Max 1.6455 gauge (I know how you feel about Forsters...but I had already ordered the damn thing before I read your other thread) and it would NOT close on the max gauge.

Should I still go ahead and get a set of Clymer's and run the headspace again or do you think it'll fire okay?
If the bolt closes on a 1.638" .308 Win. Field Reject Gage, BUT won't close on the Forster 1.6445" gage, I'm pretty sure you will be fine. Just MAKE SURE you use GOOD brass as mentioned in the OP or NATO spec brass.

Thanks from budster
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Old December 3rd, 2012, 06:03 PM   #5
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Quote:
Originally Posted by 25pilot View Post
Gus,

Thanks for the info! I'm using a NOS SA bolt, which used with this USN barreled receiver from the CMP closes on a 7.62 MIN gauge, and will not close on a 7.62 MAX or a .308 Field gauge.
Then you are good to go with .308 and probably 7.62mm ammo, but fire a few rounds of 7.62mm individually and inspect the brass just to be sure, if the ammo is not US made.

Thanks from budster
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Old December 3rd, 2012, 06:36 PM   #6
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Quote:
Originally Posted by Gus Fisher View Post
If the bolt closes on a 1.638" .308 Win. Field Reject Gage, BUT won't close on the Forster 1.6445" gage, I'm pretty sure you will be fine. Just MAKE SURE you use GOOD brass as mentioned in the OP or NATO spec brass.
Sounds good. Thanks! So is that good to shoot both .308 and 7.62 if it'll close on the .308 field reject gauge and not on the 7.62 max gauge?

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Old December 3rd, 2012, 09:31 PM   #7
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Quote:
Originally Posted by Cavtanker View Post
Sounds good. Thanks! So is that good to shoot both .308 and 7.62 if it'll close on the .308 field reject gauge and not on the 7.62 max gauge?
Normally, yes. However, there is some foreign surplus ammo like South African I would not shoot in a rifle of mine even if it did headspace like that.

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Old December 4th, 2012, 08:51 AM   #8
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Quote:
Originally Posted by Gus Fisher View Post
Normally, yes. However, there is some foreign surplus ammo like South African I would not shoot in a rifle of mine even if it did headspace like that.
Why? My Poly is at 1.640"+ and I have shot tons of SA ammo in it.

What's wrong with SA ammo?

JWB


Last edited by jbrooks; December 4th, 2012 at 10:55 AM.
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Old December 4th, 2012, 09:37 AM   #9
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On a side note concerning these 7.62 Garands.

SOME of them are unsafe to fire I found out some years ago, due to using a chamber insert instead of being re-barreled.

http://www.thecmp.org/Sales/762Garand.pdf

There were some that were changed to 7.62 by using a chamber insert in the stock 30.06 chamber.
These are the "Mk 2 Mod 0" ones.

These had problems, because it was learned that the chamber inserts can come out while firing.
This was discontinued, and these can be unsafe to fire..

I ran across some of these "in the wild" a few years back.

The ones I ran across had the same 30.06 part number on the barrel but were made into 7.62 by the chamber insert.

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Old December 4th, 2012, 06:15 PM   #10
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Quote:
Originally Posted by jbrooks View Post
Why? My Poly is at 1.640"+ and I have shot tons of SA ammo in it.

What's wrong with SA ammo?

JWB
Some of it has had bad primers and bad powder. The problem with surplus ammo is you never know WHY it was surplused for each lot that was surplused.

The only surplus 7.62mm that I have found very consistant over the years was the Portugese stuff in the plastic battle packs.

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Old December 4th, 2012, 06:20 PM   #11
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Quote:
Originally Posted by edporch View Post
On a side note concerning these 7.62 Garands.

SOME of them are unsafe to fire I found out some years ago, due to using a chamber insert instead of being re-barreled.

http://www.thecmp.org/Sales/762Garand.pdf

There were some that were changed to 7.62 by using a chamber insert in the stock 30.06 chamber.
These are the "Mk 2 Mod 0" ones.

These had problems, because it was learned that the chamber inserts can come out while firing.
This was discontinued, and these can be unsafe to fire..

I ran across some of these "in the wild" a few years back.

The ones I ran across had the same 30.06 part number on the barrel but were made into 7.62 by the chamber insert.
I saw one of the sets of engineers' prints for those chamber inserts back in the 80's. To make an extremely long story short, if there was any way that insert would have worked, they had done everything they could to ensure it would work. However, it did not work.

CMP has some Garands with the barrels that were modified by chamber insert. They are OK if you want to "complete a full collection" of Garands, but I would never shoot them much, if at all. No good reason to buy a rifle you can't shoot a lot and not be concerned about the chamber insert backing out.

Thanks from budster
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Old December 14th, 2012, 11:50 AM   #12
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Report on a CMP Navy Barrelled Receiver

Hello all. Mine arrived today and I am very pleased. It is SA21209XX.
The muzzle measures a 1 on the gage, as does the TE. The bore is bright and shiney. The park appears original with the greeny/gray hue. The barrel is SA 5-65 with the H&R stamp plus 7.62 NATO. This will make a nice shooter!

Now to the bolt. I measured hedspace with an -12SA bolt. It closes on my clymer and forster go gages but also closes on my forster 1.6340 nogo. It does not close on my 1.6380. Whew. Using a feeler gage the lug is slightly over .040" from closing.

I also have an HRA bolt that passes go, not nogo, but is better on the field than the SA.

Gus, per your discussion above, I appear to be ok with either bolt but will use the HRA. Do you have any concerns?

I'd like to get a longer bolt. What would be the SA bolt to look for, a -2?

Perhaps I should stay with the HRA since it easily passes the field reject gage.

Any inputs are welcome.

Regards, Rich

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Old December 14th, 2012, 04:44 PM   #13
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Timing issue with Navy M1

Good info big. Thanks.

Now that I have assembled a complete M1 around the Navy barrelled receiver using my accumulation of spare parts I find that the timing is way off. My timing block bottoms out without releasing the bolt. Of my other dozen or so M1s I have not seen anything so far out of whack. It appears that I have managed to use parts with a huge out of tolerance stack up. I do not even know where to start on this.

Any ideas on which part may be the leading culprit?

Rich

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Old December 14th, 2012, 06:31 PM   #14
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The real warning is to watch what ammunition you use.
As bigedp51 posted and Gus mentioned, Military grade brass should be used with the longer chambers.
While you can shoot some military grade commercial .308 cartridges in a 30-06 and walk away to talk about it. A different result may take place with a lesser cartridge.
Below are two picture of a Federal commercial .308 that was shot in some ones 30-06 next to a Federal NATO 7.62x51 case.






The commercial Federal case was on average 0.2 grains heavier than the NATO case.

The question is would the case below be able to take the same abuse.



The case to the left is from a UMC Remington green box 150gr FMJ commercial cartridge.(new)
Please note that it was compared to a once fired LC case.(what I had when the picture was taken)
The big difference is in the webbing . Notice how thin it is to a NATO case.
The weight was 10gr's lighter than the LC case.
And lastly, the neck, shoulder and most of the body was .001" thinner to a once fired case. So you get the gist of it.

Would the results of first pictures be the same with the Remington case.
I would not take that chance. So it would not be recommended to shoot it in the Navy M1 GARAND chamber Gus brought to light.

Remember Safety first, and have these rifles headspace checked.

Glenn


Last edited by geepee3; December 14th, 2012 at 07:48 PM.
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Old December 14th, 2012, 07:22 PM   #15
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More good info. Thanks.

I'm comfortable with the headspace using the HRA bolt as even though it closes on the nogo as it is no where close to closing on the field reject gage.

The ammo I have been using for for more than 10 years in my 7.62 rifles is the Portuguese NATO that comes in the battlepacks. I had the foresight to buy a case of it years ago and it is very good ammo. Also, I still have a few hundred rounds of Talon/LC 7.62 NATO so no commercial ammo will be used in this rifle.

That said I will look for a longer SA bolt to put in the rifle.

Rich

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