Remington 760 sticking when fired????

M

msinc

New member
This is a strange one...I have a Pennsylvania machine gun that sticks closed. But...it will open and eject the first round just fine. Then, you pump it and fire the second and you all but have to pogo stick the rifle to get it to open. It will open but it is not easy. Removing the magazine BEFORE trying to open it does not help. The magazine works and it loads fine. I even got Brush Research chamber hones {400 and 800} and polished the chamber. Saw no reason to, but did it anyways...couldn't find anything else. Headspace is fine and the ammo is factory with no pressure signs at all.
When I google this problem it comes up on several other forums. Several other shooters with the exact same complaint, but not a single instance where any one of them posted a remedy or positive conclusion. I don't know if this is something stupid or complicated but this rifle has not been fired much for it's age. I know that the design doesn't have much camming action leverage at all so a sticky chamber could possibly be an easy to have thing, but the fired brass is just not showing it. Because of the lack of much cam leverage I am down to thinking this thing needs to be shot "wet" {oiled} like a 1911. What happens when a 760 is fired relatively "dry"??? One person suggested that one of the cam pins fell out and the bolt is getting yanked to one side more but that don't explain the first shot working. Any suggestions or ideas are greatly appreciated and thanks in advance for replies.
 
Of all the 760's I've seen around here (Model 6's/76/7600's too), I can't say I've heard of that before.

Check out this link - you may have seen it before - some ideas here - http://forums.outdoorsdirectory.com/showthread.php/64744-Opinions-on-Remington-7600

The barrel/shims being awry catches my eye there. Never played with that myself.

I'm wondering if it's something other than the chamber/extraction end of things? Bolt stop/release sticking? Try another mag anyway just to see? The forearm slide tube binding from recoil? Just guessing out loud.

Disassembly vid -

AGI offers an armorer's course on it for $40.

Would like to know what it ends up being when you find out.
 
Thanks for the link and reply Mike B...I am about stumped...I have been doing this for a long time and can usually figure things out in a reasonable amount of time. Also, I have noticed that typically when there is something strange not making sense it's usually something out there and stupid. This rifle does not use any shims, in fact I have never seen them in any of the ones I worked on. I am not sure if that was a factory thing or not. They are used to adjust {add} headspace which is better done with the chambering reamer.
I have to agree with you on the "other than the chamber/extraction end of things"...I have looked at the brass under a pretty powerful magnifying glass and cannot see anything that would suggest sticky brass. I would hope to at least see some small spots trying to smear if that were the case. The real kick in the tail about this particular rifle is that it shoots one ragged hole. Zero issues with accuracy here. I am thinking though that when I had the bolt out of the carrier I don't remember taking out two cam pins. I will check that for certain. I will definitely keep posted on what I check and/or find. Thanks again.

Edit: I have bought a few of the AGI DVD's in the past. They are pretty good, but usually just the guy doing a complete disassemble and cleaning. They don't seem to get in to too much repair and troubleshooting, but he does talk about some of the more well known problems with different guns. I might have to get this one.
 
Sounds like rust in the chamber, grit, etc.

Auto's and pumps are hard to clean, so no one ever does it. They make a flex shaft tool that can get in there and clean. I put a new brush on the flex rod and use a drill to get the chamber clean. You can also use a product like flitz or Jb on the brush as a aid in getting some surface rust off.

Good luck
 
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I agree that rough chamber can cause this. That is why if you read my first post, one of the first things I did was buy a set of 308 chamber polishing hones from Brush Research. I also borescoped the chamber and didn't see any thing jump out at me but got the hones and polished it anyway, 400 and 800 grit. It looks like it is chrome plated now. The reflection almost blinds you in the borescope. I really wish that was the problem.
I also wish I could say that one of the cam pins out of the bolt carrier was missing but that is not the case either...I just checked it and both of them are in place. Several other guys posted on other forums about the ejection port side pin falling out during assembly. Sounded good like a possible culprit but not happening.
It just about has to be something causing the brass case to stick though...it only does it with a fresh fired empty in the chamber...this rifle, while a little strange in design, is still pretty simple. It absolutely does not bind at all empty. Maybe for some reason I got a bad batch of extra soft brass??? If I close it on an empty it opens right up. It's got me.
 
I think I got it!!!!! The rifle functions properly. Here is what I found and just as I said...it is something stupid. The 760 {at least this one} uses a ejector retaining pin that, unlike most standard spring pins or roll pins, has a split on one end and the cut section is slightly splayed to retain it. Kind of like the old first gen firing pin retainers in the M-16. The reason I was initially missing this is because the pin is held by the ejector plunger itself with the ejector spring when the gun is unloaded or for example you have the bolt out of the rifle and in your hand. But it gets released from that tension when the rifle has a cartridge chambered. Whether or not it is a loaded round or fired empty has the same effect, the pin is no longer being held in place by the ejector plunger and spring. If, in the case of this rifle, the ejector retaining pin looses its own tension then the pin is free to drift out of place and interfere with the locking lugs in the barrel extension when a round or case is in the chamber. That explains why it was intermittent, the first round I fired would always open no problem. The pin finally drifted far enough to cause trouble by the second round and once the action was forced open it would slam partially back into place when the action was closed. It remained out of the way and the action would seem fine because apparently it took recoil to cause it to drift far enough.
I'm not saying this is what is wrong with all of the others with this problem the guys on other forums posted about, but it is what was wrong with this one. Key word "was"!!!!!
I learned a couple other things regarding the 760...in February of 77 they changed the barrel thread to a left hand thread. This don't make a lot of difference to the average Joe but if you're a gunsmith and get one to rebarrel you will need to make sure you are cutting the threads the correct way. It's 7/8"X20 by the way and only about 4 or 5 threads hold the barrel on!!!
The next thing I learned was that the barrel extension and lug must be indexed perfectly to the bolt or you not only alter headspace but also if it's off enough the bolt might close and not want to open. The lugs can be too far one way and either not let the bolt close enough to the barrel {more headspace} or not allow the bolt to cam around far enough to get released. This is a real pain to check for because the rifle has to be reassembled to see if it is correct or off.
Thanks again fellas for your replies.
 
Wow nice troubleshooting. Glad you got it figured out! That rifle sounds like quite the contraption. Some of those old designs sure make ar15's look simple don't they.
 
Interesting msc. On those barrel threads, you're talking the threads that hold the bbl. extension on the barrel at the chamber end, correct? Not the ones at the pump tube/lug holding the whole assembly onto the receiver? I'd need to see a diagram (will dig one up later) to envision completely what is going on there inside the bolt body that you're talking about.

Thanx for the update.
 
Thanks for the nice comments fellas!!! The rifle is for sure a strange design. I guess like anything else it is not really made to be taken apart that far and or have custom barrel blanks fitted. I cant for the life of me figure out why they went with that method to attach the barrel. Seems like they could have just threaded the receiver and screwed the barrel on like normal people. But yeah, you are right an AR is a walk in the park compared to this thing.
Yes I was referencing the actual barrel to the extension when I was talking about the ones being left hand after Feb.77. That thread is also "timed" which means it starts in a certain spot so that the open sights are on top dead center of the barrel when the extension and lug is torqued into place. You know the old saying, "god looks out for dummies" well that is the case with the last one of these I rebarreled for myself in 260. I was unaware of all these problems and the thing went right together, headspaced dead on and shoots great.
This rifle uses the same style ejector as a 700. Its just a spring loaded plunger straight down into the bolt face. The bolt body is cross drilled just like a 700 but for some strange reason {again, Unless it's not factory} they didn't just use a conventional roll pin. That would be about right though...they didn't do much of anything "normal" on this model. Thanks again fellas!!!
 
Thanx for sharing again, man! We're gonna talk about that 260 you built again sometime! I still think a lite wt. stainless bbl., aluminum (or even polymer like a Glock or Benelli Nova) receiver, and synthetic-stocked pump carbine would be the ultimate PA mountain gun.
 
Originally Posted By: pyscodogDang, I don't even own a 760 but learned a bunch from this thread. Got job!!

Thanks!!!This one sure taught me a lot too!!! Thanks to the link from Mike B. One thing I never realized is that the so called "dust cover" is really not a dust cover per se... even the factory calls it that, but it is used to keep the right side bolt cam pin from falling out of the bolt carrier. In that link one of the posters talks about his cam pins being "staked In" but the factory didn't do that because how would you ever get them out to remove the bolt from the carrier??? A lot of people talk down on the fact that this little dust cover is "plastic junk" but it turns out that they originally were metal on the early rifles but changed to plastic to make the gun silent...apparently the metal cover made a rattle noise that people thought might spook game. I guess it's hard to call a rifle the "Gamemaster" if it chases all the deer away!!!
 
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