Just coming back from range. Trouble cause identified!
The jamming was caused by the broken magazine. There was a "bubble" on the mouth of the magazine, which causes feeding and ejecting issues. After careful checking, I found there was a crack on the magazine wall. With this crack, the magazine mouth by itself was not strong enough to hold its shape and was damaged by the rim of the cartridge.
After identified this issue, I tried a good 1934 magazine in this M1914, fired 150 rounds (including 50 Serbian made JHP) -- everything worked without any trouble.
Early 1914's magazine with this type of bottom must be hard to find
