Thread: Keyholing and stiff bolt lift

My son has a new toy, 1900 Spanish Mauser rebarrelled by their military to 7.62-51 in 1950.
Bore and crown look ok. So he bought some Greek surplus ammo for it and off we went to the range yesterday
First 3 shots went ok, but the bolt got progressively harder to lift. Last 2 the projectiles went sideways and really
Hard to eject. Ejection marks on cases. Too hot obviously
My question is - Why did it get progressively worse ?
Why didn’t the first projectiles tumble ?
I’ve loaded up some nice soft loads with Sierra 150 gr spitzers to try next range day.