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longhair51
February 21, 2009, 17:54
I contacted Forster about these gages and received this message,

Dear sir,

Thank you for the inquiry. We do make these gages...we make a 7.62 NATO gage (minimum chamber) and the 7.62 NATO (maximum chamber).

The gages are $27.40 each plus shipping and handling.

If you are interested in placing a phone order on Visa or MasterCard, please give us a call at 815-493-6360 from 8-4 Central time, Monday thru Friday. We will be glad to assist you.

Regards,
Dee

Forster Products


Would I be better off with these gages , or .308 win gages? I only shoot millitary surplus, and load milsurp brass.

Don

W.E.G.
February 21, 2009, 18:01
I think the nominal dimension for the Forster 7.62 "go" gage is 1.632"

By contrast, I think the nominal dimension for the Forster .308 "go" gage is 1.630"

So, which one is best for you depends on which number you want to work from.

1811GNR
February 22, 2009, 15:24
Got this info from Forster back in June:
"7.62 NATO (Minimum chamber) – length is 1.6355” plus .0003” minus zero P/N HG762NATOMin

7.62 NATO (Maximum chamber) – length is 1.6455” plus Zero minus .0003” P/N HG762NATOMax

The gages are available directly from Forster for $26.00 each plus shipping and handling.

If you would like to place a phone order on Visa or MasterCard, please give us a call at 815-493-6360 from 8-4 Central time."

WEG put the smackdown on me when I posted this before because the max is way big. The max dimension Forster is using is the gauge used with a test bolt in a M14 to determine if the receiver is unserviceable. From what I can find in the M14 TM and "The FAL Rifle" 7.62 NATO max should be 1.6405".

.308 gauges from Forster are 1.630" Go, 1.634" No Go, 1.638" Field.

W.E.G.
February 22, 2009, 15:43
I'm thinking 1.6455" would give a LOT of misfires, and certainly head separations with new COMMERCIAL brass.

sturmgrenadiere
February 22, 2009, 15:46
I ordered a set of the 7.62 NATO gauges from Nurmrich/e-gunparts the other day. Was a buck or two more each than Forster, and I received Forster gauges (didn't see them on Forster's web page prior to ordering, I guess it pays to ask).

Got them just to have them. I have otherwise always had Forster .308 gauges.

Question 1…

What does it mean whey they say they are "plus .0003” minus zero" or "plus Zero minus .0003", respectively?

Question 2…

A search did not reveal what I was looking for, so I ask, what is the danger of too tight headspace aside from maybe a high primer causing a negligent discharge when chambering, or the prevention of chambering/locking?

I ask because I shoot 7.62 NATO surplus, like many of us. I stocked up back in the day when it was WAY cheaper than any .308 out there. I have many thousands of 7.62 NATO cases for reloading.

Every arsenal manual (the Canadian tech pubs, the Brit method of head spacing, etc) are all based on 7.62 NATO specs. They didn't headspace with .308 limits as concerns. If the headspace was too tight for 7.62 NATO, then the rifle was rejected until corrected.

So I ask, what is the danger of too tight a headspace with 7.62 NATO, or is there any?

Now, I write this having shot many hundreds of rounds of 7.62 NATO out of rifles I have build using .308 WIN min headspace with no ill effect. But I always wondered if it ever contributed to some slow to break in rifles that had chambering and extraction issues early on?

Bottom line, if one is to never shoot .308 out of their rifle, why bother with the .308 specs? From a safety “what-if” standpoint, having a rifle safely fire both rounds is a good idea, but beyond that, what’s the benefit?

Regards

Ben

W.E.G.
February 22, 2009, 16:03
Comes down to this:

The tighter the fit of the case in the chamber, the more likely you are to optimize accuracy.

Looser fit usually delivers better reliability when the mechanism is dirty.

Its always a trade-off.
Your gun. You decide the application and objectives.

Don't get hung up on .308 vs. 7.62.
Nomenclature means little to an educated shooter.

In the context of the FAL, one should know the nominal measurement of his rifle's chamber, and he should know the nominal measurement of his ammo.

There are tools for this.
Headspace gages are just part of the tool set required to be fully knowledgeable. At a minimum, you have headspace gages to measure the chamber, and you have to have a tool for measuring the base-to-shoulder on your ammo. Also advisable to have a tool to measure base to rifling for the different bullets you may fire.

From there, you decide whether the relative fit is acceptable.

sturmgrenadiere
February 22, 2009, 16:10
I know all that, but thanks anyway. I was looking to see if there was a more "technical" reason. I know this periodically gets beaten to death.

In the mean time, can anyone chime in on the ZERO minus .0003 stuff?

shortround
February 22, 2009, 16:14
Originally posted by sturmgrenadiere
I know all that, but thanks anyway. I was looking to see if there was a more "technical" reason. I know this periodically gets beaten to death.

In the mean time, can anyone chime in on the ZERO minus .0003 stuff?

That is the manufacturing tolerance for the gage. Plus zero minus .0003 means that it won't be any bigger than the stated dimension but might be up to .0003" smaller. Minus zero plus .0003 means that it won't be any smaller than the stated dimension but might be up to .0003" bigger. You have to have a tolerance for even a gage or it would be prohibitive to manufacture.

sturmgrenadiere
February 22, 2009, 20:19
Ah, that makes sense. Thank you very much.

1811GNR
February 22, 2009, 21:14
Originally posted by shortround


That is the manufacturing tolerance for the gage. Plus zero minus .0003 means that it won't be any bigger than the stated dimension but might be up to .0003" smaller. Minus zero plus .0003 means that it won't be any smaller than the stated dimension but might be up to .0003" bigger. You have to have a tolerance for even a gage or it would be prohibitive to manufacture.

This is the same explanation I got from the nice folks at Forster.

Say you have a rifle with the HS set at .308 minimum and you get some max length 7.62 ammo, could the ammo chamber and decrease the size of the case and cause some pressure problems?

yovinny
February 25, 2009, 05:16
FWIW;


USGI "field reject" FSN# 4933-647-3698 (sized 1.6455")
USGI "no go" FSN# 4933-916-9275 (sized 1.6375")
USGI "go" FSN#4933-916-9271 (sized 1.6355")
*referenced from USGI manual #TM 9-1005-223-34

"field reject" is made to use with a special test bolt only and is used to determine recievers that are stretched beyond being servicable.

Cheers, YV

1811GNR
February 25, 2009, 12:55
What about this one? Pretty sure it is the GI "Field" length. Picture lifted from AR15.com, can't recall posters name.