I took out my LR308 for the first time today. Barrel is marked 7.62x51. Shot a box of Tula .308 no problems. Then switched to the milsurp ,that came with the rifle. Headstamped with the NATO cross, F, 78, and 4B. About the 10th round a fired casing stuck in the chamber BAD. Tapped it out with a AK cleaning rod, had to tap damn hard. Anybody know what kind of ammo this is? There was no obvious damage to the casing once it was extracted.