My first guess would be residue from firing built up on the barrel, preventing the round from being in contact with the barrel steel. (fully chambered).
The action was still able to close enough to allow firing, but with the case not fully flush against the barrel it blew out the small gap.
This could easiiy result in the ruptured case looking like the gap was larger than it was due to the gas pressure opening the action a little during the blowout.
OR it might have been a couple of bad rounds. Unlikely to get more than one at a time, though.
I once had a Remington round blow out of the rim, in my 10/22. Not just ahead but acutally out of the rim itself. Case body (with no rim at all) was left in the chamber, found a disc of brass in the action (the rear face of the rim) and the extractor went bye-bye into the weeds.
Bad round, obviously. Only happened the one time, of of the tens of thousands of rounds I've fired from that gun.
Clean the breechface and the rear face of the barrel specifically and everything else in general and try again.
If it happens again, you've got a gun problem that needs to be investigated and repaired.