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Barrel-Cylinder Gap ???

Discussion in 'Handguns: Revolvers' started by Hawkmoon, Jun 22, 2005.

  1. Hawkmoon

    Hawkmoon Well-Known Member

    Can anyone give me an idea what the largest SAFE barrel-cylinder gap should be (or can be) for an inexpensive Peacemaker clone in .45 Long Colt? I have one on which the gap can be measured visually rather than with a feeler gauge. Not sure if I want to test fire it. (Well, actually I do know that I do "want" to test fire it ... I just don't know if I should.)

    How difficult is it to move a barrel deeper into the frame?
  2. Sheldon

    Sheldon Well-Known Member

  3. Father Knows Best

    Father Knows Best Well-Known Member

    The generally accepted standard for B/C gaps on single action revolvers used with smokeless ammo is .003 to .006. Larger gaps may work just fine, but you'll lose some velocity and have more gases blowing out the gap. On the other end, I have several single actions with gaps as small as .0015, and they work just fine, also. The only problem I have with the small gap is that on one of them (a Uberti/Navy Arms 1875 Remington replica chambered in 44-40) I have to be VERY careful when reloading to keep OAL of the rounds down, or the bullet nose will protrude from the front of the cylinder and hang up on the back of the barrel.

    Also, there is a debate about whether larger gaps are needed or advisable for use with black powder. I know some 'smiths who recommend a gap of .003 for smokeless and .008 for black powder. I often shoot black powder cartridges in several revolvers with gaps ranging from .0015 to .004, however, and have never had a problem with fouling at the B/C gap.

    If you think the gap is unusually large, you should measure it and have a reputable 'smith advise whether he thinks it is unsafe. If for whatever reason you want it closed up, the 'smith will set the barrel back. Generally, the barrel is set back one full turn so the front sight doesn't need to be moved. Once it is set back, however, the rear of the barrel needs to be faced (cut back) to ensure it is square to the cylinder and the gap is at whatever you want it to be. Then the forcing cone will likely need to be recut (because facing the barrel took off the rear of the forcing cone.

    It's not a difficult job. In fact, you can do it yourself with tools from Brownells. It takes a little time and patience, however. Any good 'smith can do it for you, too. I'd estimate a total cost of $75-150 depending on what's involved with your particular gun.
  4. jaybar

    jaybar Well-Known Member

    Max gap?

    Revolvers shooting lead bullets will generally start to "spit" when the gap exceeds .010". Anything greater than .013" is usually considered unacceptable and should be corrected.
  5. Hawkmoon

    Hawkmoon Well-Known Member

    If it is truly not a difficult job I am inclined to take a stab at it, but don't know how to proceed. I know how to remove the barrel from the frame, but after that is the barrel chucked in a vise and cut bak the equivalent of one thread pitch, or is the face of the frame milled off by that dimension? I have Brownells new catalog here -- what tools should I be looking at?

    TIA. The gap on this pistol exceeds .013 so I guess I should do something. It would be a shame to just use it as a wall decoration.
  6. JB in SC

    JB in SC Well-Known Member

    SAAMI maximum is .012".
  7. Hawkmoon

    Hawkmoon Well-Known Member

    Okay, this one is well beyond the recommended maximum. How do I go about setting the barrel back one turn?
  8. Old Fuff

    Old Fuff Well-Known Member

    The job can be more complicated then some seem to think. You need a barrel vise with the correct blocks to fit the barrel and frame. If the blocks on the barrel slip while you are trying to turn it the finish will likely be scared. If the frame isn't properly supported it can be bent or warped. Once the barrel is removed you must determine exactly how much metal to remove so that the shoulder will be set back the amount you want and position the barrel so that the front sight will end up at 12:00 when the barrel is tightened. You will also have to buy the tooling to re-cut the throat. If you take this to a gunsmith be sure he as both experience and the right tools. If you do the work yourself,the tooling may cost as much as the gun, or even more.

    A blotched job may leave you with a ruined gun.
  9. Father Knows Best

    Father Knows Best Well-Known Member

    I was assuming he had what he needed to remove and reinstall the barrel without damaging it, as he seemed to indicate that he knew how to do it.

    Cutting back the shoulder is the hardest part. I would leave that to a professional. Refacing the barrel and recutting the forcing cone, however, are easy jobs. Brownells has barrel facing and forcing cone kits that will cost abotu twice what you'd pay a 'smith to do the job for you. I bought the tools because I seem to acquire another single action revolver every other month or so, and I find that almost all of them (generally Italian imports) could use this work. I generally open the gaps to .006, cut 11 degree cones, and polish the cones, but of course I'm setting mine up for black powder cartridges and soft lead bullets. I have never attempted to set a barrel back by myself (haven't needed to, as all the gaps I've come across have either been o.k. or too small, but not too big), and don't think I would.

    Incidentally, I also end up recutting a lot of chambers and throats. My revolvers are mostly 44-40, and I've found that the SAAMI spec 44-40 chamber is often too small in the neck for .429 or .430 bullets in modern brass. That's because the original barrel groove diameter for 44-40 was .4265 +/- .0005, and standard bullet size was .427. Most 44-40 guns these days, however, have .429 barrels (same as .44 Special/Mag), which require .429-.430 bullets for best accuracy and minimization of leading. My solution was to have a custom 44-40 cylinder chamber reamer made up that is .002 oversize in the neck. I can now load .430 lead bullets in thick brass (like Starline) and have no trouble chambering them.

    Throats are another issue. About 1 in 3 single action revolvers I measure have inconsistent or undersized throats, so I will often open those up, too (they should be barrel major/groove diameter +.001/-.000. Rugers are particularly notorious for having undersized throats, which destroy accuracy.
  10. Hawkmoon

    Hawkmoon Well-Known Member

    Thanks for the replies so far. I'm still trying to decide if this is something I dare tackle myself.

    If I want to take off enough material to set the barrel back exactly one turn -- how much is that? I assume the clones use the same thread pitch as the real Colt SAA, since they mostly claim to be parts-compatible. How many threads per inch would that be? In other words, to set the barrel back one turn, how much would I have to cut off the shoulder?

    And since the intent is to set the barrel back to close the gap, why would I then want to reface the end of the barrel after setting it back? wouldn't that undoing what I just did?
  11. brickeyee

    brickeyee Well-Known Member

    "And since the intent is to set the barrel back to close the gap, why would I then want to reface the end of the barrel after setting it back? wouldn't that undoing what I just did?"

    You need some gap to allow for cylinder rotation. The odds of having the correct gap after setting back one thread are pretty much zero. The barrel will interfere with the cylinder closing.
  12. thatguy

    thatguy Well-Known Member

    You haven't even tried it yet? Has anyone else shot this gun? Did it work OK? How big is the B/C gap, you didn't mention. Barrel swapping can be tricky and setting one back to tighten the gap involves some serious machining. I have swapped barrels but I wouldn't care to attempt setting one back.

    I have a S&W M&P that runs .011 and works just fine. I have been told that up to .012 is within factory specs although they shoot for .003-.006.

    I sure wouldn't be rushing into extensive repairs without at least shooting the gun first.
  13. Hawkmoon

    Hawkmoon Well-Known Member

    thatguy --

    The gun is a clone, but has a replacement cylinder that doesn't match up right to the frame. The gap as it sits is .075" -- which leaves me a trifle reluctant to test fire it. If it were over SAAMI minimums by .001 or .002 I'd fire it, because it's not going to see heavy use (by me) anyway, but that large a gap seems a but farther out of spec than I feel comfortable playing with.
  14. thatguy

    thatguy Well-Known Member

    That (.075) is excessive. It may cost more than the gun is worth to fix it. Why was the cylinder swapped? Might be cheaper to try a different cylinder for fit. Sometimes you get lucky. A local gunsmith may have a box of parts with a cylinder to try. You might contact the manufacturer and explain the problem and see what they say. In our litigious society sometimes they will just send a new part to make the gun safe rather than risk a lawsuit.
  15. Old Fuff

    Old Fuff Well-Known Member


    Take my hint and spend a little money ... :cool:

    On a book .... :eek:

    "The Colt Single Action Revolvers - A Shop Manual. Vol. 1 & 2." by Jerry Kuhnhausen.

    It can be obatined from: www.gunbooks.com or www.brownells.com or maybe Amazon.

    It contains text and illustrations on, "complete S.A.A. revolver repair, rebuilding, and mechanical restoration," including the popular clones (except Ruger).

    Thereafter you will know everything you need to know too do anything, including fitting a new barrel. Thread specifications are included. :)

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