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Thread: Sticky bolt on marlin 39

  1. #61
    Boolit Grand Master uscra112's Avatar
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    I'm back to what I hypothesized at Post #43, that the cartridge head was swelling, enabled by the hammer not backing up the bolt. After all pressure is released, the swollen head is wedging the bolt against the cam. Not wishing to be thought a nag, but I still want to see rim thickness measurement before and after firing.

    For that matter, what happens if you return one of the swollen cases to the chamber (I know it's a pain) and close the bolt. Do you meet resistance before the lever is all the way home?
    Cognitive Dissident

  2. #62
    Boolit Grand Master Bazoo's Avatar
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    I measured some of the cases and they were normal in size, though I don’t recall the size. They are swollen some though and show the firing pin indent as well the square portion or the pin below the protrusion.

    I have closed the bolt on a fired case and don’t recall anything out of the ordinary, but I will try a few more next time I fire her.

    One point, part of the spare parts I want is a firing pin, so when I get one, testing of these hypotheses will continue.

  3. #63
    Boolit Grand Master uscra112's Avatar
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    Diameter will of course be that of the chamber, less maybe a thou. If the rim thickness gage shows even a thou or two over headspace, I think that's the answer.
    Cognitive Dissident

  4. #64
    Boolit Grand Master Bazoo's Avatar
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    What do you mean rim thickness gauge? You mean, if I measure a fired rim and it was any over headspace?

    I wish I’d had sense to save some of the cases, they are all in the weeds and mixed with others though. But the drive to fix it precluded sense to fully document the issue.

  5. #65
    Boolit Grand Master uscra112's Avatar
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    Something like this:

    https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

    For generations it's been known that the thickness of the rim, which is a function of the accuracy of the machine operation that forms it, has a significant effect on the accuracy of the shooting. Competition shooters use a tool like this to sort through their ammo and cull out any rim thickness outliers. In these days of ammo dearth, sorting commodity ammo like your Remington would yield positive results.

    The other thing they sort for is overall weight of the cartridges. Remington is well known for loading bullets that weight a full grain above or below the nominal weight.

    I'm in no way a competition shooter, but accurizing commodity ammo has intrigued me for years. I've used various kludges to measure rim thickness in that tikme, but I finally broke down and ordered the one I linked to. I like that it can be used with a dial indicator as well as a digital caliper.
    Cognitive Dissident

  6. #66
    Boolit Grand Master Bazoo's Avatar
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    I mostly do plonking of tin cans and such, so I don’t need the increase of performance offered by sorting of ammo. If I want consistency for longer range I generally use better ammo. I haven’t tested the gun for accuracy for the latter yet.

    I spose I could sort via rim, and just plink with the outliers. I may give it a shot and see if it’s worth it. I have heard that measuring bullet diameter offers as much or more advantage as weighing.

  7. #67
    Boolit Grand Master uscra112's Avatar
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    With a tool to precisely measure rim thickness, you could detect any axial bulging of the case head. If you found some that were bigger than your known headspace, they would be acting as a spring to put pressure on the cam surface, making it hard to open. The bulging would result from the bolt being forced back with sufficient force to deform the action elastically, letting the brass distort along with it. The brass having a much lower yield strength than the steel, would want to stay in the bulged shape, while the steel springs back to trap it. That's been my hypothesis for several posts now.

    As I posted earlier, this is a known problem with centerfire actions that lock the bolt at the rear. The steel between the case head and the locking surface is a spring. Actions like the Mauser that lock at the front have an extremely short spring that is extremely stiff, where rear-locking action like the Savage 99 are less so. Thus they do not handle hot loads nearly as well.

    I'm now curious to know about axial bulging of cases fired in blowback semi-auto actions like the 10/22 Ruger. Unfortunately I sold mine, since it shot patterns and not groups, no matter what I did. So now I have nothing to experiment with.
    Cognitive Dissident

  8. #68
    Boolit Grand Master uscra112's Avatar
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    Bullet diameter is crucial. Most consumer grade .22s like the Marlin have fairly loose chambers, so as to handle any sort of ammo they may be fed. One thing that yields results with commodity ammo is to swage the cartridge in a die to make the bullet O.D. a consistent .2250", so it fits the "sporting" chambers better. This is commonly called "bumping". Many shooters do it to just create a different nose shape. There are tools on the market to do this. If you have a small lathe, or access to one, you can make a tool yourself for a lot less money. I drew up a design which I have been sharing around. It's just two parts that fit into a Lee "Universal Expander" (which it isn't) die body that retails for fifteen bucks. P/M your regular email addy and I'll send you a copy of the drawing.

    A problem of late is finding a shellholder for .22 rimfire. They do exist, but nobody has any these days. A lathe can make one most of the way, but you need a mill to finish it. If I had CNC, I'd go into production, but my machine tools are manual and ancient. I made one for myself, but it took the better part of an hour.
    Cognitive Dissident

  9. #69
    Boolit Grand Master Bazoo's Avatar
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    Uscra, I think you had mentioned wedging of the bolt. After studying it a bit, I bet what was happening was, the firing pin, being hit at an angle was driving into the firing pin keeper, and then moving the bolt forward. Depending on the ammo, it gave bolt thrust sufficient to lock the action.

    I’m considering ways to test this hypothesis.

  10. #70
    Boolit Grand Master Bazoo's Avatar
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    Had one lock the bolt today. After about 200 rounds. I disassembled the bolt and there was some machine marks on the firing pin and true keeper rivet. I polished that area of both. Testing will continue.

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Abbreviations used in Reloading

BP Bronze Point IMR Improved Military Rifle PTD Pointed
BR Bench Rest M Magnum RN Round Nose
BT Boat Tail PL Power-Lokt SP Soft Point
C Compressed Charge PR Primer SPCL Soft Point "Core-Lokt"
HP Hollow Point PSPCL Pointed Soft Point "Core Lokt" C.O.L. Cartridge Overall Length
PSP Pointed Soft Point Spz Spitzer Point SBT Spitzer Boat Tail
LRN Lead Round Nose LWC Lead Wad Cutter LSWC Lead Semi Wad Cutter
GC Gas Check