Instead of angling up into the chamber the bolt pushes it so it angles down and cannot be chambered. Is this common?
Yes, it's common. It's called a double-feed. The rim of the top cartridge is hanging up on the rim of the cartridge below it. This problem is endemic to all rifles that use a box magazine with rimmed cartridges; it happens to Lee-Enfields too.
Mosin-Nagants have a device called an interruptor built into the LH wall of the receiver. It holds down the next cartridge while the top cartridge is chambered, preventing double-feeds. If you're wondering what it looks like, it's a 2-piece sheetmetal doodad held on by a screw; it also functions as an ejector, so many sources call it the interruptor-ejector.
The problem is that when you load the last round, the magazine spring is near the bottom of its travel, so it's hard to push the 4th round down hard enough to engage the interruptor-ejector. The trick is twofold- push harder
, and push on the rear
of the top cartridge. Pushing on the middle
of the cartridges often won't compress the mag spring fully, preventing the 4th cartridge from engaging the interruptor-ejector.
Don't worry about breaking anything by pushing hard; remember, these aren't decadent bourgeois capitalist rifles we're talking about here. Mosin-Nagants are built to take the abuse.
Most modern sporting rifles are based (if only somewhat) on the Mauser 98 and use rimless cartridges, preventing double-feeds.