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March 21, 2011
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Okay guys I gave the Model 77 as good of a cleaning job as one can of blaster cleaner could do. Blew a lot of black stuff out of it and cleaned the bore and chamber with solvent and brush. I also disassembled the magazine tube and cleaned it thoroughly inside as well as the inside of the outer magazine tube. Today when test firing I had an issue where the empty case would extract halfway and the bolt would stick. I was able to push the bolt back shut and then it would manually operate after I dumped the remaining 14 rounds from the magazine tube. I started over again with five rounds in the magazine tube and it worked perfectly, as it did with six, seven, and eight rounds. When I loaded 10 Rounds the same thing happened with the empty case extracting only halfway and the bolt sticking open. When I tried it with nine rounds the empty case was extracted and ejected but the next round was stuck halfway under the bolt. After clearing the magazine and getting the crushed round out from under the bolt I tried loading eight rounds and it worked perfectly five times in a row.
I suspect the magazine spring is putting excess pressure on the incoming rounds causing this feeding issue since I’ve noticed the magazine tube gets sort of snug when sliding it in with 10 or more rounds loaded. No excess friction noticeable with only 8 rounds.
Does anyone know what length the magazine spring should be? When i installed it after cleaning it was about 5 inches or so longer than the tube.
I’m considering trying again with a full magazine, 15rds, but installing the tube all but 3 inches or so. Maybe that will help me decide if the spring length/tension is the problem and how much I might cut it.
Darrin
April 30, 2023
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I’m assuming there’s no dent or ding in the magazine tube around that 9-10 round point, like even a small one?
March 21, 2011
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Jeremy P said
I’m assuming there’s no dent or ding in the magazine tube around that 9-10 round point, like even a small one?
Nothing at all that I’ve noticed. It really wasn’t too dirty either. The inside is shiny and the spring appeared perfectly uniform it’s full length.
Darrin
April 30, 2023
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This will sound stupid but flip that spring 180 degrees and see if anything changes…
If you decide to replace the spring, a replacement spring for a model 72 should be really close fit if you can’t find a listing for the spring…most sites only show the clip fed 77 if I remember correctly. (Full disclosure, I’ve not done a 72 spring in a 77 before personally…just a thought.)
March 21, 2011
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I like your line of thinking Jeremy. I have a 72 also I may just try it, if its the same length not sure if it is, to see if it behaves similarly. Thanks.
Darrin
April 30, 2023
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Yes, that’s an easy experiment then at least. Let us know!
January 20, 2023
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Might Wolfe Springs not have a replacement spring? Then you could have something to cut down and try before working on the original. They are the go to outfit for gun springs and I would consult them and Brownell’s by phone.
- Bill
WACA # 65205; life member, NRA; member, TGCA; member, TSRA; amateur preservationist
"I have seen wicked men and fools, a great many of both, and I believe they both get paid in the end, but the fools first." -- David Balfour, narrator and protagonist of the novel, Kidnapped, by Robert Louis Stevenson.
March 21, 2011
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Ok Bill, i scanned their web page but saw nothing related to this spring. I looked hoping to find a dimension or length. I will call them today. Last eve I loaded a full tube of 15 rds and left the inner mag tube out by 2 3/4″, just enough to clear the muzzle. It functioned ok, not ideal but different than before. I was left with the impression that less spring pressure was better. I didn’t push the tube in after firing the first 7 or 8 rds and then the last 2 rds hung up under the bolt when firing. I’m of the opinion I may have a couple different things going on there that may facilitate removing the bolt to ensure there’s not something else causing issues, ie grime or improper re-assembly after a previous workover.
Seems like a tremendous effort for a notoriously problematic firearm.
Darrin
January 20, 2023
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Darrin, I applaud your diagnostic efforts. The reason I suggested Brownells is that for many years they offered technical advice from one of their in-house gunsmiths just for the asking. I used them once years ago and they were extremely helpful. That was their chief advantage over Midway.
There is something niggling at me about the business of the magazine spring. I know it’s frustrating to have some idiot who isn’t there telling you what to do and that’s not my intent. But bear with me while I explain what confounds me.
My very limited understanding of spring dynamics is that a captured magazine spring exerts maximum force when it is at full compression. When the magazine is full, the force the spring exerts on the entire cartridge stack presses hardest on the nose of the 15th cartridge. The force exerted on the nose of the 14th cartridge is marginally less as soon as the 15th cartridge escapes past the stop. The force exerted on the nose of each remaining cartridge in the stack is progressively less by some decrement as soon as the cartridge ahead of it is fed to the carrier.
I don’t know whether the decrease of force is linear, quadratic, sinoidal or what — but we can say it is less on cartridge 1 than cartridge 15.
If the magazine spring were overstrong and pushing cartridges hard enough to jam the mechanism, would the issue not first arise on the feeding of cartridge 15, which receives more force than cartridge 7 ??
Magazine springs can weaken over time, particularly if kept under compression. I don’t think they can grow stronger. I don’t discount that this one may be an incorrect replacement but, if it is the original spring, I don’t see how it could be a cause of jamming by exerting too much force.
Going at it from the other direction, whatever the cause, the bolt is not able to move fully back but stops in place, presumably blocked by something. Can you set up a jam, leave the jam in place and shine a light up past or around the carrier to see whether something is physically bearing on the bottom of the bolt? The action is a blowback so there’s no breech locking mechanism that could foul it.
If anything, I would continue to investigate whether the fault lies partially in the spring not moving the 7th and earlier cartridges past the stop snappily enough.
Thanks for hearing me out patiently.
Best,
Bill
- Bill
WACA # 65205; life member, NRA; member, TGCA; member, TSRA; amateur preservationist
"I have seen wicked men and fools, a great many of both, and I believe they both get paid in the end, but the fools first." -- David Balfour, narrator and protagonist of the novel, Kidnapped, by Robert Louis Stevenson.
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