Remington 760 Jam

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Remington 760 Jam

Post by Macd »

During my load testing of IMR4227 and pistol bullets I experienced a jam like I have never had before in this rifle. I believe it was caused by a combination of factors but the shorter OAL of the cartridge with the pistol bullets was the primary cause. I was racking the slide to eject a fired case when the bolt simply just stopped any further rearward movement with the fired case just barely clearing the ejection port. A visual inspection of the area in front of the bolt showed nothing so I removed the mag and racked the bolt forward and slowly racked it back and it stopped again. I then noticed my mag was down one round that I hadn't fired. I pointed the rifle down and the round fell out from inside the receiver. Here is what it looked like.
35 Damaged Rnd.jpg
It apparently came out of the mag when I had racked the slide forward on the previous round and then got pushed into the receiver when I racked the slide back. Sure glad the primer never hit anything back there. :o
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Re: Remington 760 Jam

Post by Ranch Dog »

Oh, my! Sometimes being lucky is better than being good!
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Re: Remington 760 Jam

Post by GasGuzzler »

Might be over-pressure it were to light off.
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Re: Remington 760 Jam

Post by Ranch Dog »

GasGuzzler wrote:Might be over-pressure it were to light off.
Not sure the effect of not being chambered, other than the brass not containing it. I did a quick check of his load with QL with a 158 TC Rainier seated flush with the case mouth and the calculation indicated about 26K PSI. Not sure what happens when the cartridge is unsupported inside the receiver.
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Re: Remington 760 Jam

Post by mr surveyor »

just my somewhat uneducated guess but it looks like an obvious case of poor neck/bullet tension. Either the brass neck sizing has an issue, the bullet itself (possibly with no cannelure) is either undersized diameter, or the bullet (being lightweight) has insufficient length/bearing surface to allow for necessary neck tension ....

just what I would consider ...


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Re: Remington 760 Jam

Post by GasGuzzler »

Ranch Dog wrote:
GasGuzzler wrote:Might be over-pressure it were to light off.
Not sure the effect of not being chambered, other than the brass not containing it. I did a quick check of his load with QL with a 158 TC Rainier seated flush with the case mouth and the calculation indicated about 26K PSI. Not sure what happens when the cartridge is unsupported inside the receiver.
Good point. Kinda like an unwrapped firecracker.
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Re: Remington 760 Jam

Post by Macd »

mr surveyor wrote:just my somewhat uneducated guess but it looks like an obvious case of poor neck/bullet tension. Either the brass neck sizing has an issue, the bullet itself (possibly with no cannelure) is either undersized diameter, or the bullet (being lightweight) has insufficient length/bearing surface to allow for necessary neck tension ....

just what I would consider ...


jd
I will give more thorough report on the bullets in the thread on using pistol bullets in the 35 Remington. The bullets are seated to the crimp cannelure which puts the flat base just above the bottom of the case neck. They are crimped in place with a heavy crimp as they are .357 rather than .358. I tested every round and all were held tightly.

The 760 has a rotating breech bolt which is attached to a carrier with a much smaller diameter shank. When fully closed there is a lot of space in the receiver to the rear of the carrier. A case loaded with a normal rifle bullet is too long to get in behind the closed bolt but apparently the shorter pistol bullet tipped case can. The jammed round popped out of the magazine when I chambered the previous round. This may indicate a weak magazine spring allowing the short round to move too far forward in the magazine due to recoil or the racking action. Because I was shooting a pistol powder that only took up 70% or less of the case I was pointing the rifle up to position the powder better against the primer. I believe this caused the loose round to fall into the space behind the breach bolt carrier. When I racked the slide to eject the spent case of the previous round I drove the breech bolt edge against the bullet of the errant round driving it back into the case. The above picture is not clear but there was a lot of damage to the case mouth. Here is a picture of the damage to the bullet. This bullet was never chambered so the only danger was the primer being set off by a protrusion in the back of the receiver. The result would be interesting to say the least.
760 Jam Bullet.jpg
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Re: Remington 760 Jam

Post by mr surveyor »

That was a very good explanation and makes good sense to me now.

Thanks for helping me understand the issue.


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