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Measuring cylinder/barrel gap?

Discussion in 'Blackpowder' started by ClemBert, Apr 17, 2011.

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  1. ClemBert

    ClemBert Member

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    What's the consensus here for the procedure to measure cylinder-to-barrel gap on BP revolvers? Do you measure with the hammer down then push back on the cylinder with all your might while using the feeler gauge? Or, do you measure with the hammer cocked?

    Also, what is the ideal cylinder-to-barrel gap for efficient shooting with minimal binding due to fouling?
     
  2. junkman_01

    junkman_01 member

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    Cock the hammer and hold the cylinder back against the recoil shield. I've always considered .005-.010 inches as perfect in a C&B revolver.
     
  3. ClemBert

    ClemBert Member

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    I measured a few of mine...too lazy to measure the boxed ones. This is what I got using that method:

    (I got crap...so I deleted it and am going to start over....)

    Is it typical that the revolvers with tops straps are a bit tighter?
     
    Last edited: Apr 17, 2011
  4. junkman_01

    junkman_01 member

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    Are you sure you are getting the decimal point in the right place? All your listed gaps are very tight, except the last one.
     
  5. ClemBert

    ClemBert Member

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    Deleted due to breathing too many sulpher fumes. :)
     
    Last edited: Apr 17, 2011
  6. SleazyRider

    SleazyRider Member

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    Your post sent me out to the garage for a feeler gauge, and my relatively new 1858 Pieta Remington measures .011" with the hammer fully cocked and cylinder pushed to the rear. My cylinder gets tight after about a dozen rounds of FFF black powder, but I wipe it down with a wet rag and I'm good to go again. What puzzles me is how dirty the cylinder pin (axle?) gets---how does all that powder residue get in there?
     
  7. ClemBert

    ClemBert Member

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    Wait a minute! LMAO....my feeler gauges have been out in the garage in the heat and humidy and they are stuck all together. Lemme unstick them and get back to you....LOL!!!!

    p.s. I'm gonna erase the previous numbers in a lame attempt to cover up my stupidity.....:eek:
     
  8. ClemBert

    ClemBert Member

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    Okay, here are the "real" numbers. :banghead:

    0.0040 Ruger Old Army
    0.0065 Pietta 1851
    0.0035 Uberti 1858
    0.0050 Pietta 1858
    0.0080 Uberti Walker w/ cap-n-ball cylinder
    0.0120 Uberti Walker w/ Kirst cylinder
     
  9. junkman_01

    junkman_01 member

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    That's more like it. The Ruger is a bushed cylinder, so it is in a different category than the others. All the others seem good, but the Uberti 1858 is a bit on the tight side. ;)
     
  10. SAA

    SAA Member

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    Side pressure from the bolt can affect measurements, so I prefer to measure at half cock.
     
  11. TheRodDoc

    TheRodDoc Member

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    I would say the .008 and .012 for the walkers is to big of gaps. You are losing a lot of pressure through those gaps.
    I set mine at .003" for my walker and it works fine.
    I probably would choose .004" for your Kirst version due to the fact it might get hotter then the other.
    It seems everyone here thinks the gap can foul shut and cause binding. That Can't happen no matter what the gap is. The chamber pressure will always blow through the gap keeping it open. The fouling will always be thinner then the gap.

    What causes the binding is the hand spring.
    All the repo guns seem to have way to stiff of hand springs which push the cylinder ahead against the fouling that does stick to the cyl. face. That fouling makes a very good brake lining and that spring is putting the brakes on. Enough that you have trouble cocking the gun. You need to thin the original spring or make a new one. It should only be strong enough to move the weight of the hand itself to the cyl. and not push the cylinder ahead.

    Even the ruger spring some are putting in is to stiff.

    You can prove this to yourself by shooting your gun till you think the cyl. face bound it up. then put the hammer at half cock. hold the cyl. back with one hand then hold the gun up toward the sunlight and site through the gap. You will see that no matter where you turn the cyl. the gap will still be there.

    A chart I made to show the area of some different gaps and a equal circle or hole with the same area to give you an idea of the pressure that you might be loosing at 6 to 12 thousandths gaps.
    [​IMG]
     
    Last edited: Apr 18, 2011
  12. SleazyRider

    SleazyRider Member

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    How does one adjust the gap on, say, an 1858 Remington?
     
  13. madcratebuilder

    madcratebuilder Member

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    The old Colt specs called for .006-.008 for the cap and ball revolvers. You can run a closer gap but risk binding if you have any powder residue build up. Colt had this problem with the Walker and changed the forcing cone shape with the Dragoon model for less surface area contact.

    I've shoot these with as much as .018 gap and see little or no difference with the same model at .008.

    To close the gap you have to set the barrel back, fairly easy on a open top, requires machining on a top strap model.
     
  14. SleazyRider

    SleazyRider Member

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    Thank you, Madcratebuilder.
     
  15. ClemBert

    ClemBert Member

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    On an open top what is the process to set the barrel back? Likewise, what is the process to increase the gap?

    I suppose one way is the screw the barrel in or out? But, for the open tops I suppose you'd remove the barrel pins then take a little off the mating portion of the frame?
     
    Last edited: Apr 18, 2011
  16. arcticap

    arcticap Member

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    Adjustability

    There's another way to close the gap without permanently
    altering the frame as recently described by Smokin'Joe in
    Post #99 on page 4 of the following thread:

    http://www.thehighroad.org/showthread.php?t=575472&page=4&highlight=cutting

    Will this method work with the conversion unit? :rolleyes:


     
    Last edited: Apr 18, 2011
  17. ClemBert

    ClemBert Member

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    A round cylinder shim is an interesting idea and not a bad one at that.
     
  18. ClemBert

    ClemBert Member

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    If this is the process then I'd have more questions:

    1. How hard is it to remove the barrel pins and do they get ruined when you remove them?
    2. Wouldn't you need a wider wedge as the distance between the barrel slot and the arbor slot contact points would increase?

    Y'all have really peaked my interest now as to your gunsmithing skills and how you increase or decrease the barrel/cylinder gap.
     
  19. junkman_01

    junkman_01 member

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    I did this once to my ASM 1860. I took some metal off the barrel lug to close the barrel/ cylinder gap a little and then added a set screw in the end of the arbor to adjust the wedge slot. You can not use a wider wedge because a wider wedge will not fit into the barrel window.;)
     
  20. ClemBert

    ClemBert Member

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    All tips on all the wedges on mine are narrower than the barrel slots. Assuming a wider wedge still has a tip narrower than the barrel and arbor slot then it should pop right in.

    I unboxed a new unfired Pietta 1860 I have and measured the gap to be 0.0125". Kind of wide for an unfired steel open top. Maybe it'll be my first experiment on shrinking the gap.
     
  21. junkman_01

    junkman_01 member

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    It will go in but.....the slot is now longer to the front and the wedge will have nothing to bear against to draw the barrel tight to the frame. The arbor slot has to be adjusted to the rear.
     
  22. junkman_01

    junkman_01 member

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    Fire it a few times first.
     
  23. ClemBert

    ClemBert Member

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    That doesn't seem to be the case for my revolvers. On my revolvers the front facing end of the arbor slot is not even with the front facing end of the barrel slot. The front facing end of the arbor slot sits rearward from the front facing end of the barrel slot. From mine it appears to be around 0.055 - 0.065 from a couple of revolvers I looked at. This means that as long as you don't adjust the barrel rearward by more than 0.055 - 0.065 you will still have the front part of the arbor slot to bear against.
     
  24. ClemBert

    ClemBert Member

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    I'm going to borrow makos_goods' awesome CAD illustration to show that delta. It's the measurement from the front of the wedge to the front of the barrel slot in his illustration.

    [​IMG]
     
  25. junkman_01

    junkman_01 member

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    That may be the case on your revolver, but it sure wasn't the case on my ASM !
     
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