The older the gunpowder the more likely it is to have deteriorated and create burn rate instability. That is every once in a while, it goes from deflagration to detonation. Gunpowder does not burn like a candle, but people think it does. Shift the exponential curve a bit with conflicting pressure waves and high pressures occur in the case.
Shoot it over a chronograph and see if the velocities are in line with original issue ammunition.
For German ammunition standards, as a reference, from
Mauser Bolt Rifles by Ludwig Olson, 3rd edition
German 7.9 mm Model 88 cartridge
Bullet diameter: 0.318”
Bullet weight: 227 grs
Muzzle velocity 2034 fps (29.13” barrel)
German 7.9 mm Model S cartridge
Bullet diameter: 0.323”
Bullet weight: 154 fps
Muzzle velocity 2936 fps (29.13” barrel)
Max pressure: 44,082 psi
Velocity of S cartridge in 23.6 inch K98 barrel:
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German 7.9 mm Model sS cartridge
Bullet diameter: 0.323”
Bullet weight: 198 fps
Muzzle velocity 2575 fps (29.13” barrel)
Max pressure: 46,926 psi
Remarks: muzzle velocity with 23.62” barrel is 2476 fps
Old surplus ammunition is sold as "day old bread" to gullible Americans who don't know that old gunpowder will blow up your firearm. All you have to do is search for posts and videos to find those who have had high pressure problems and indications, and also, those deniers who want this to be true.
So, when you shoot the stuff, look for signs of gunpowder deterioration and high pressure indications.If it produces higher than spec velocities, the pressures are higher too.
Someone's experience with surplus ammunition.
notice at 10:44 Ian’s stock cracking
And a couple of machine guns have blown up with Turkish ammunition.
WW2 4831 in the case. Gotta be safe, right?
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powder looks good, except for the corroded brass stuck to it, Must be good, right?
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This powder was kept in a cool and dry basement by the owner, who purchased it in the 1950's. He gave me a can, and close to ten years ago I shot it in 2014. It took less powder to reach max than new IMR 4831. Only shot five shot groups over the chronograph, nothing jumped out for ES and SD, but you know something, I don't trust the stuff. And that was before I pulled these bullets in 2022.
this powder did not look too bad. Maybe a bit gummy.
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the owner gave me a handful of these cases at the range. And this is only 1969 gunpowder, young stuff compared to pre WW2 powder.
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Understand this, the risk is on you. You lose a gun, a hand, an eyeball, the seller is not going to help you at all. Buyer beware with this old stuff. Sure, it does not go kaboom each and every time, sometimes a takes a lot of rounds down range to find the extra special round. But it happens.