Went out to the range today... Think my 7.62x51 ammo is questionable.

I got some loose 7.62x51 nato ammo that is of unknown (probably eastern european?) origin. Went down to the range today hoping to burn some of it up in my bolt action rifle, but after 10 rounds I noticed that the primers were really starting to look "popped" after being fired... From too high of pressure, I can only assume? Some pictures of the spent casings below:





The primers seemed seated well in the rest of the ammo, so I put her away. Am trying to get a hold of some other "factory" ammo to try in the gun to see how it works, as I assume it is the ammo that is questionable. I think these cartridges are stamped "FNP" or something like that, and the one scrap of paper on the box they came in said 7,62 instead of 7.62 so I figure it is european make.

Thoughts?

Historically, European ammo gives optimum performance at -40° F . Shooting it at warmer temperatures can be invigorating but not dangerous.

What rifle are you shooting.??

I would say it's a head space problem.

Primers backing out are usually less pressure. If it was high pressure the case head would slam back and smash the primer and head stamp.

Fire a round in a revolver with no bullet and the primer pops out and you can not open the cylinder.

FMP is Portuguese ammo. I have several battle packs and it is pretty high pressure also bullets attract a magnet. I think they made it to function in LMG's. Joe

The bolt action rifle is one of those Chilean surplus mausers in 7.62x51 NATO. Probably need to go get the headspace checked on her.

Interesting ammo. You can see where it was annealed up by the neck (the pictures don't show it well but you can see it with the proper light).

If it has the NATO cir-cross , it is NOT loaded to higher pressure. NATO M59 and M80 7.62 ammo is 50,000psi MAX , which is under SAAMI .308 Win pressure limits.

I've shot thousands of FNM , (Fábrica Nacional de Munições de Armas Ligeiras, Chelas, Portugal) aka Port/Portugese , in my Springfield Armory M1A and DPMS LR-308.

It's some of the best surplus ammo out there.

HOWEVER!

There is another FNM headstamped ammo out there. Fábrica Nacional de Municiones, Santa Fe, México.

Never use any ammo from a country where ya wouldn't drink the water!

I just went and checked. It DOES have the NATO cir-cross stamped on it. Other than that it just says "FNM 78-7"

FNP is Spanish mfg I think (Palentia (sp) national arsenal). But what ever the ammo is,,something is amiss there.

It does look like excessive headspace. The case gripping the wall of the chamber and the primer sets back.
Excessive pressure can sometimes reveal itself in a situation of excessive headspace where the case head sets back and reseats the primer,,but the forward portion of the case remains firmly gripped to the chamber walls.

That stretches the brass at the thinning point just above the case head. You start to see a faint ring there and can usually feel one inside with a wire pick.
Sometimes they separate on the first firing,,sometimes after a loading or two.
Head separation of the case is not a happy situation for the rifle or the shooter.

A very weak load can make for the condition as well.

Both conditions can warn of excessive headspace with the amount of primer setback the picture shows.

Since you don't know what the load is (milsurp ammo) or how it may have been affected by storage over the years,,I'd start by getting the headspace checked on the rifle and at least either eliminate that as a cause or bring it to the surface.
IIRC, headspace gauge dimensions for 7.62Nato is very slightly different from 308Win.

Fixing it can be expensive. Proper reloading techniques for the individual rifle can over come it.
..and it could be just that particular ammo that is the problem.

Vegetaman said:

I just went and checked. It DOES have the NATO cir-cross stamped on it. Other than that it just says "FNM 78-7"

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Made in July 1978.

I'd suspect excessive headspace too.

Is it a '95 (small ring) or '98 (large ring) Mauser you have?

Chile converted a ton of '95s , but they really shouldn't be used with 7.62 ammo.

I went and checked the gun further. It is stamped "Waffenfabrik Steyr Austria" on the side, along with "Modelo 1912-1961 NATO" on the top. Straight bolt. Don't mind the hand, just had to hold it at a weird angle to get the light right so you can read the stampings.



Also appears the top of the barrel has "M12 308 GERMANY" and some sort of other import mark on it?

Large ring Mauser '98. That's fine for the round.
I'd just start by checking the headspace.

These rifles were converted from 7x57 IIRC.
Nothing wrong with that, thousands of them probably done. They just made use of existing rifles to upgrade in the early post War years to NATO caliber.

2152hq said:

Large ring Mauser '98. That's fine for the round.
I'd just start by checking the headspace.

These rifles were converted from 7x57 IIRC.
Nothing wrong with that, thousands of them probably done. They just made use of existing rifles to upgrade in the early post War years to NATO caliber.

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Will a standard go/no-go gauge for 7.62x51 NATO work on this? Or do I need to check somehow else to figure out my headspace?

If there is something wrong with it, what could it be? Internal wear? Was wrong to begin with?

Your help is much appreciated, sir.

Probably will have to take this one to my gunsmith of choice soon if I can't figure it out myself.

Comparing water to bullets is kinda wrong. Would you drink the water in any former Yuglav countries? They make some of the best most accurate AK ammo!!

To the OP, eastern european countries dont make 7.62 nato. PPU makes 308 and its actually quality made ammo

Sent from my DROIDX using Tapatalk 2

Vegetaman said:

Will a standard go/no-go gauge for 7.62x51 NATO work on this? Or do I need to check somehow else to figure out my headspace?

If there is something wrong with it, what could it be? Internal wear? Was wrong to begin with?

Your help is much appreciated, sir.

Probably will have to take this one to my gunsmith of choice soon if I can't figure it out myself.

Click to expand...

Sir, I don't know about now, but 7.62 (as opposed to .308) gauges used to be hard to find. Assuming you can find them, they should be fine in your rifle. One trick, though: You'll want to hook the rim of the gauge under the extractor claw before easing it into the chamber.

If you have a .308 case gauge, check some unfired rounds from that batch of surplus in it. Though 7.62 headspace is longer (by about 4 thousandths, IIRC) than .308, some 7.62 ammo is made to .308 external case dimensions. That could explain what you're seeing.

Hope this helps, and Semper Fi.

Ron H.

If it passes a .308 No-go or Field then the rifle is fine.

The Steyr 1912-61 is a Steyr 1912 fitted with a rechambered 03A3 barrel, usually a 2-groove.

If you have a .308 case gauge, check some unfired rounds from that batch of surplus in it. Though 7.62 headspace is longer (by about 4 thousandths, IIRC) than .308, some 7.62 ammo is made to .308 external case dimensions. That could explain what you're seeing.

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The chambers are different between .308 and 7.62, but all the ammo I have seen is made to the same external dimensions. The reason for the generous size of the 7.62NATO chamber is to ensure reliable operation of semi and full-auto weapons in extreme conditions. 7.62 NATO ammo is specced to have thicker brass at the head to reduce the chances of a head separation when the extractor in a semi or full-auto gun yanks it out when the gun is dirty.

I know someone with a .308 case gauge at least, so I may at least check the ammo. I'll have to see if I can find a .308 no-go or field gauge.

Thank you all; much appreciated!

A Standard 7.62 Nato guage set is what to use. Many 'smiths will substitute a 308Winchester commercial cartridge guage.
There are a couple .000" difference in a couple of the dimensions as I recall. Some say it's fine to do so, others cringe at the thought!

Excess headspace could be the bolt locking lugs have set-back into their locking surface/seats in the receiver. That can come about from excessive pressure loads or even normal use.
Mausers seem to suffer from bolt set back more than other bolt actions as they are case hardenend (surfaced hardened) and not through hardened steel.
If the surfaces in there aren't deeply hardened, they quickly indent. Some models were notorious for the fault,,the Peruvian Mauser rifles were one. Even the Argentine 1909 model rifles seem to be prone to it. Both of these are Model 98 types and highly desirerable in original form and as actions on which to build sporters.

I could be nothing more than a mis-matched bolt. Not uncommon for the bolts to thrown in a pile so to speak during cleaning & field maint situations and when reassembled,,they didn't always get the matching bolt back in the rifle.
When the original rifle was made, or the conversion done,,the bolt is matched to the rest of the parts to ensure correct headspace.
It's a matter of a couple .000" one way or the other being a GO or a NO-GO,,so a mis matched bolt can easily cause the problem.

You can check of sorts for bolt lug set back yourself.
You must strip the bolt of it;s firing mech first. You just want the bolt body itself,,no firing pin, spring, cocking piece, ect.

Cock the rifle and put the safety in the middle, straight up position.
Remove the bolt from the rifle.
Push the bolt lock plunger on the left side of the bolt shroud in, and unscrew the bolt shroud. It'll come out the back of the bolt body with the firing pin, spring with it.

Now you have just the bolt body w/extractor. You can take the extractor off too, but it's not really necessary and can sometimes be tough to get back onto the bolt body.

Place the stripped bolt body back into the rev'r and close the bolt.
Now with your fingers of your left hand put some rearward pressure on the bolt body.
You want the locking lugs of the bolt pressed against their locking surfaces in the receiver.

You can't get much of a grip and you really don't want much.
You are just seeing if the locking lugs of the bolt are imbedded into the receiver in any amount.

You will feel that when you gently and slowly lift the bolt handle. Watch the bolt body very carefully as you lift the handle.
See if it moves FORWARD just a touch as the bolt handle is lifted.
By the same measure as you close the bolt do it slowly and watch to see if the bolt at the last closing rotation moves BACKWARD and sets in any amount.
If it does these things,,there is bolt lug set back in the receiver.
In some situations you can feel the bolt snap into and out of the set-back recesses in the receiver as you more quickly manipulate the bolt up and down.

With that said,,nearly all Mausers display some,,even faintly when you look at those surfaces with the bbl pulled out of the recevr.
Upon proofing, they may set back a tiny amount and stay there. The amount not noticable during operation and not enough to effect headspace specs.

But some receivers are damaged beyond that, and some are so deeply set back that even normal rounds will actually lock the bolt shut as the brass expands and holds the bolt in those recesses. Trying to lift the handle to overcome that is near impossible sometimes as it demands pushing the brass case forward in the process.

Worth taking a look for. A simple matter to field strip the bolt and take a look at the insides of that too while you're at it.

Sorry for the long post.

It could be nothing more than a mis-matched bolt. Not uncommon for the bolts to thrown in a pile so to speak during cleaning & field maint situations and when reassembled,,they didn't always get the matching bolt back in the rifle.

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Mismatched bolts on South American Mausers are a result of those countries trying to keep the number of coups down. The bolts were often stored separate from the guns and when the guns were to be taken out, matching of the bolts and guns simply did not happen.

Okay, I did just as 2152hq described in his post, and unscrewed the firing mechanism from the bolt (with the safety "UP"). It was a bit dirty inside, so I cleaned that (it was a pain to take it further apart to clean it, I daresay). However, in playing with the now plain vanilla bolt in the action, I did not notice any truly noticeable front or back motion when working the bolt up and down (at least for that first partial turn). There was a bit of play if you pushed the bolt back and forth from the locked position (all the way down) in the action, but once I put the firing mechanism back in the bolt, that mostly seemed to go away.

Everything about it seems mostly smooth and tight, to my totally untrained eye... As I said, with the firing mechanism removed from the bolt, there is some front to back play if you wiggle the bolt forward and backwards, but when going from locked to up a bit and then back down, I don't see any forward/backward movement when pressure is kept by my left hand against the bolt mechanism.

Welp... I still feel confused.

I also had some WWII reenactment blanks I ran through this gun about... 6 months ago. Checked 'em, and I see no signs of primer popping (which I guess doesn't surprise me?).

To avoid possible personal injury, take the rifle to a reputable gun smith and have the head space properly checked.