How does a double feed happen in a bolt rifle?

Just a few I have seen...

1. Extractor failure - fails to remove the spent case properly before the operator tries to load the next.
2. Bad magazine - bent lips or overly strong floorplate spring allow two cartiridges to move forward together under friction.
3. Rimmed/Belted Magnum cartridges - the rounds are not loaded with the upper cartridge rim forward of the lower cartridge rim. Upper rim catches the lower rim and drags it forward.
4. Dumb Luck (or lack thereof).
 
Just a few I have seen...

1. Extractor failure - fails to remove the spent case properly before the operator tries to load the next.
2. Bad magazine - bent lips or overly strong floorplate spring allow two cartiridges to move forward together under friction.
3. Rimmed/Belted Magnum cartridges - the rounds are not loaded with the upper cartridge rim forward of the lower cartridge rim. Upper rim catches the lower rim and drags it forward.
4. Dumb Luck (or lack thereof).

The .303 british cartridge fools a lot of young guys. I have seen personally a moose run out and stop, the guy with me trying to close the bolt on his Lee Enfield while the moose is staring at us. After the moose ran away I pulled his mag and gave him a lesson on how to load the Lee Enfield magazine. It can happen with the Mosin too if your not careful.
 
3. Rimmed/Belted Magnum cartridges - the rounds are not loaded with the upper cartridge rim forward of the lower cartridge rim. Upper rim catches the lower rim and drags it forward.

I honestly had no idea about this, and I've been shooting belted magnums and 303's for twenty years...Definitely makes sense though. I've never had problems with the belted magnums, but the 303's, occaisionally.

I'll have to learn some new habits I guess.
 
The worst I saw was a Rem 700. Push the non belted case forward and it would 'pop' up and the next shell would have its nose in the action also. I figure it looks like a log jam. That was the first hunt with that gun. According to Remington warranty it could not be fixed and I was SOL. Will not buy another. Ever. Also if you take a mauser action and make a custom like a 404 then you may see this as the action is small for the cartridge.
 
Double feed due to mechanical problem.

-You push the bolt forwards to chamber a round out of the mag and the round below it moves forwards and up into the feed ramp. You then get two cartridges jammed up in the front reciver ring. This is worst with belted cartridges and rimmed cartridges. The protruding belts/rims get caught up on the round below. A fix is to load your cartage's longer if and if possible almost touching the mag box. This stops the second round from moving forwards as it hits the end of the mag box after a very short distance.

-You pull the bolt back and the extractor does not catch the round and pull it out of the chamber. The bolt is pushed forward pushing a second round out of the mag and it rams in to the base of the round in the chamber jamming the rifle.




Double feed due to operator error

-You feed a round into the chamber and do not close the bolt. Not closing the bolt leaves the round in the chamber as the bolt needs to be cammed closed to get the extractor to grab the rim (remington). Then you pull the bolt back and try to feed another round which rams into the base of the first jambing the rifle.

-You open the bolt and pull it back, but not far enough to eject the shell before pushing it closed again. The original shell remains on the blot face and jambs up itself OR (especially on rimed and belted) the original shell strips a second round out of the mag and the two jamb up on the feed ramp as the bolt is closed.
 
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