Almost certainly corrosive. Brush it out with hot soapy water, then clean normally. Anything that touches powder residue (bore, bolt, and inside the receiver). Make sure to oil when done, and check back for the next few days.
The ammo is corrosive and it kicks like a mule. None of my mausers liked it much. As I recall this ammo will let you know if your firing pin spring is in good shape. The primer cup seems to be real hard
As others have said, 1950s vintage Yugo M49 7.92mm Heavy Ball ammunition. Brass cased, berdan corrosive primers. Some hang fires and some will require a second firing pin strike to fire. I still have several cases left from when they were giving this stuff away years ago... shoots decently out of my Yugo 24/47 out to 500m.
Not much 8mm surplus around anymore...or any other contemporary calibers. It is better than not shooting at all.
Clean with a water/Ballistol mixture to remove the salt created by the chlorate primers and you will be GTG
FWIW, the powder is EXTREMELY dirty. I bought a bunch thinking I would shoot it up... I don't mind cleaning after
corrosive primers, but with this, firing just 20-40 rounds required *extensive* scrubbing with brush/solvent/patches
to get past the carbon and down to where the corrosive salts are on the steel. After a couple of experiences with that,
I pulled the bullets, dumped the powder, and kept the brass/bullets for reloading. At the price it was selling for back
in the day, just the bullets were more than worth it... Hope this helps,