Case headspace gauges--WHOA!

[Old Dog]

Mine SA M1A is old.  Compared to most of 'em, real old.  1979.  Which doesn't say a thing about the headspace or chambering, it also has a commercial NM barrel on it (original to the rifle) rather than a used military barrel so many folks seem fond of.

Anyway, for the question that I'm wondering about now - why in the world does SA chamber their rifles for .308 Winchester dimensions and then tell you to only shoot GI 7.62 NATO?  Evidently 7.62 Nato ammo fits the shorter .308 chambers fine.

Something else just hit me.  Does anyone make 7.62 Nato reloading dies?  Or is it a be careful and adjust your .308 Winchester dies "just so" to insure your brass is correctly (and minimally) resized for your 7.62 Nato chambered M1A clone?

I'll be honest.  I've never measured my brass before I shot and the only measuring I've done after resizing is when setting up a case trimmer. 

I've "heard" alot of new info over the last few months that talk about things I've never heard of before.  Right now all I've done is resize and trim and primer pocket swage a bunch of brass.  When I start loading it and shooting these new reloads I'm going to pay attention to some things I never looked at before and see what's going on.  Thanks for the info.

[ken grant]

 All the 7.62 Nato ammo I have ever tried fit into a .308 chamber O.K. but Nato spec chambers are much larger than .308.
I have all the Specs. in my loading room somewhere. I will try to find them tomorrow.
Another thing you will find is the fact that .308 ammo is loaded to higher pressures than 7.62 ammo.
This info is on the Web but offhand I can't tell you where.
I don't know of any 7.62 Nato dies being made by anyone.
I do remember that a .308 Field gauge is about the same as a 7.62 Go gauge.

If you have a case guage, measure a few rds. fired with the gas OFF and a few with the gas ON and see the difference.

Fulton Armory has a good page on their site about loading for M14/M1A's. It is worthwhile to look up.

[ken grant]

 Found the specs for .308 and 7.62 chambers

       .308                            7.62                               7.62 Match
Go   1.630 +.002            1.6355 +.0005               1.6355 +.002

N/go  1.634                    1.6405 + .0005              1.6385

Field   1.638                    1.6455

Best I can remember( don't hold me to it) Nearly all Springfield's have 1.632 headspace tags on them when new.

[ken grant]

 I still have a couple of thousand rds. of 7.62 ammo of different types.(sold all the rest)
I will measure a sample of each tomorrow with a Precision Mic and see what the measurements read.

[wcmartin1]

Found the specs for .308 and 7.62 chambers

       .308                            7.62                               7.62 Match
Go   1.630 +.002            1.6355 +.0005               1.6355 +.002

N/go  1.634                    1.6405 + .0005              1.6385

Field   1.638                    1.6455

Best I can remember( don't hold me to it) Nearly all Springfield's have 1.632 headspace tags on them when new.

You're right, Ken, I found the headspace tag that came with my rifle and it states:

"This rifle has been headspaced to 1.631 according to current GI specs.  This headspace requires the use of GI mil spec ammunition or good commercially manufactured ammunition that meets GI specs."

Perhaps that's why I am fortunate enough to get four to five reloads with my brass when resizing to .308 dimensions.   In addition, here is an interesting excerpt from the FAQ at Fulton Armory's website:

"Clint, What's the difference between .308 Winchester & 7.62x51mm NATO?

Jerry Kuhnhausen, in his classic Shop Manual (available from Fulton Armory; see the M1 Rifle Parts & Accessories or M14 Rifle Parts and Accessories Pages under Books) has published a somewhat controversial recommendation concerning .308 Winchester and 7.62x51mm NATO ammo, headspace & chambers. I broached the subject with him some months ago. He had his plate full, so we decided to chat on this in the future. When we do I'll report the results of our conversation.

I completely agree with Jerry that if you have a chamber with headspace much in excess of 1.636 (say, 1.638, SAAMI field reject), you must use only U.S. or NATO Mil Spec Ammo (always marked 7.62mm & with a cross enclosed by a circle) since the NATO mil spec calls for a far more "robust" brass case than often found in commercial (read .308 Winchester) cartridges. It is precisely why Lake City brass is so highly sought. Lake City brass is Nato spec and reloadable (most NATO is not reloadable, rather it is Berdan primed). Indeed, cheaper commercial ammo can fail at the 1.638 headspace (e.g., UMC) in an M14/M1 Garand. Many military gas guns (e.g., M14 Rifles & M60 Machine guns) run wildly long headspace by commercial (SAAMI) standards (U.S. Military field reject limit for the M60 & M14 is 1.6455, nearly 16 thousandths beyond commercial (SAAMI) GO, & nearly 8 thousandths beyond commercial (SAAMI) field reject limit!).

I also agree that 1.631-1.632 is a near perfect headspace for an M14/M1A or M1 Garand chambered in .308 Winchester. But I think that it also near perfect for 7.62mm NATO!

I have measured many, many types/manufacturers of commercial and NATO ammo via cartridge "headspace" gauges as well as "in rifle" checks. If anything, I have found various Nato ammo to be in much tighter headspace/chamber compliance than commercial ammo. Indeed, sometimes commercial ammo can not be chambered "by hand" in an M14/M1A with, say, 1.631 headspace (bolt will not close completely by gentle hand manipulation on a stripped bolt, although it will close & function when chambered by the force of the rifle's loading inertia), though I have never seen this with NATO spec ammo. I.e., if anything, NATO ammo seems to hold at the minimum SAAMI cartridge headspace of 1.629-1.630, better than some commercial ammo!

So, why set a very long 1.636 headspace in an M14/M1A or M1 Garand? It probably is the conflict mentioned above. Military headspace gauges say one thing, SAAMI headspace gauges say something else, as do the spec's/compliance covering ammo. In a court of law, who will prevail? I think Kuhnhausen gave all those who do this work a safe way out. However, I believe it not in your, or your rifle's, best interest. Whether you have a NATO chambered barrel (M14/M1 Garand G.I. ".308 Win."/7.62mm NATO barrels all have NATO chambers), or a .308 Winchester chamber, keep the headspace within SAAMI limits (1.630 GO, 1.634 NO GO, 1.638 FIELD REJECT). This subject is a bit confusing, and for me difficult to explain in a one way conversation!

Clint McKee"


I like the part that says -

"I also agree that 1.631-1.632 is a near perfect headspace for an M14/M1A or M1 Garand chambered in .308 Winchester. But I think that it also near perfect for 7.62mm NATO!"

- since mine is set to 1.631

Edited to add -

I'm still going to use surplus (mil spec) or Federal brass exclusively due to it's stronger construction, though.

Regards.

[Son of Martha]

OK, more info.

I tried some FACTORY ammo in the case gauges.  Interestingly enough, most of it checks bad.

So, in order to fix my problem, I have decided to just throw the damn gauges away--I was much happier without them...
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(Just kidding)

Instead, I am at this point using them in an "advisory" capacity...they do pretty well telling me which cases I will likely have problems on.  When even factory ammo (which gauges about .003" long in the .223 gauge) fails, yet works fine in every .223 I have tried, it's time to apply some fuzzy logic.

Got an RCBS small base X-die, even it doesn't resize enough for these torture devices.

YMMV

SoM

[Nickle]

Regular RCBS dies do size enough to fit the ammo in the gage.

Now, you've got to remember that ammo tolerances are less than chamber tolerances, to the point that Max tolerance ammo must fit in a Min spec chamber.

And, the bottom line is simple. If it fits in your rifle (or rifles), then it's close enough.

[wcmartin1]

OK, more info.

I tried some FACTORY ammo in the case gauges.  Interestingly enough, most of it checks bad.

Make sure that it is not the cartridge rim that is causing them to hang up in the gauge instead of headspace problems.  I have had this happen with a burr on the rim or one that was slightly enlarged (even on new brass) or warped.

[Old Dog]

It's a wonder I survived.

I used play with one piece of brass (lubing as required) till I got to the point where it had a small little line of dark lube at the point where the neck meets the shoulder.  Then I'd wipe the case off and see how well it chambered.  If it chambered alright I set it aside and marked it at my "set up case for use the next time I reloaded that cartridge. 

I did the same with an empty case with a seated bullet.  Seat the bullet till it fits in the magazine and then gradually adjust the bullet seating die to get the bullet down to the point where it just kisses the riflling.  Then that one got set aside as the "set up guide" for that cartridge and that bullet.

May not be real scientific and it didn't cost much but it worked for my M1A with NM barrel and my 03A4.

[Nickle]

Pretty much what we do when we custom make ammo to fit a customer's rifle.

We clean the shoulder with steel wool, start with the sizer die backed well off, then start tightening until we just start to mark the shoulder.

Then when we seat the bullets, we start by cleaning the bullet area that touches the throat with steel wool, then seat and try and tighten and repeat until we just quit marking the bullet.

[LabRat]

What wcmartin1 said. I've recently had some 5.56 brass that wouldn't even get the case rim into the gauge. Freaked me out a little until I noticed that they had a burr on the OD of the rim, which prevented them from going all the way into the gauge. When I took a fine file out and removed the burr on a couple, they dropped right in and were in spec. I threw them away anyway, as it wasn't worth the time to hand-file these cases and it's a potential weak point on the rim that could lead to a failure to extract, but it was instructive that it wasn't necessarily the dies or brass at fault.

I have had some problems with certain makes of brass not functioning well on the first reloads. I had some PMC .308 that I was reloading for a 700. I resized them along with some other commercial headstamps, mostly R-P and Winchester. In the gauge, they were probably 1 or 2 thou longer than the other headstamps but still within spec, so I went ahead and loaded them. At the range, more than half of them would not chamber. Well, you could, but you would've had to really crank the bolt. Needless to say, I didn't fire them and just tossed the brass and salvaged the components. Near as I can figure, the PMC brass had a thicker case near the head and wasn't resized the same with the die at the setting that worked for the other brass. Or, it could've been the opposite, with the thinner case near the head being bulged slightly and not being resized by the die and therefore not chambering if the 700 had a slightly tight chamber (.308 not 7.62 NATO). Don't know as the brass is long gone and I didn't really think of checking these possibilities until after, but it does show the importance of sorting and checking the brass, because outside they might all look the same, but inside, not so!