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These rifles were designed for "controlled feeding." That is, the cartridges are first put into the magazine, and when the bolt is pushed closed it strips a cartridge from the magazine. When the bolt goes forward, the face of the bolt pushes the head of the cartridge forward and the rim of the cartridge slips BEHIND the extractor.
If you try to simply drop a cartridge into the breech, (which, from your posts, it seems like this is what you are attempting,) then the extractor will not pop over the rim from behind, thus it will not fully close on the cartridge.
This is a feature that is found on most older military rifles, such as the Mauser and p-14/m-17 rifles.
Although not an absolute certain way to identify the difference is that the p-14 rifles have a large "broad arrow" ownership mark on the left side wall of the action. Also, p-14 extractors have a narrow hook on the end of them while the m-17 extractor is full width at the hook. I have, however, seen a p-14 that someone had replaced the extractor with a m/17 one and then wondered why it did not work.
If all else fails, take it to a good gunsmith.
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