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Thread: Barrel Drop Clearance

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  1. #1
    Join Date
    1st June 2004
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    Lexington, North Carolina...or
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    Barrel Drop Clearance

    Because we're likely getting close to a small flame war on the Barrel Fitting
    thread here, I wanted to address this in a new thread. Although every smith has his or her own methods, sometimes there are better ways to get where we're goin'.

    Let's look at the practice of modifying the slide in the noted area for the purpose of obtaining barrel drop clearance.

    Although the Army Ordnance Department gave it the go-ahead, it was usually done on slides that needed more material removed from that area to start with. Simply put...those slides were not to spec. Also keep in mind that
    weapons were subject to regular inspections...including gauge checks and
    parts replacements...whether or not there was an actual problem with the part, especially if the weapon was slated for duty in harm's way. The old adage: "When in doubt...Throw it out." applies.

    The point is that, the US military had vast inventories of spare parts to work with. If the work resulted in an unserviceable slide, it was a matter of grabbing another one and rebuilding the weapon. If you follow the advice of the manuals...which give a general overview of the modification...and you wind up with a broken slide, neither Kuhnhausen nor any of the other authors of instructional texts are going to write the check to replace it.

    The second thing to consider...and carefully...is that material removal there in a slide that IS cut to spec, or very close, is that it thins the cross-section in an area that not only absorbs a lot of stress when the gun fires, it's adjacent to a sharp corner. Anyone who understands that sharp corners make a chunk of steel more prone to cracking will see the problem here. The area just under the radius is essentially a strengthening rib. If you'll look closely at it, you can see that, rather than increasing the entire radius, the corner that is formed by the radius and the rail can be lightly flattened, and a shallow flat filed on the mating surface along the side of the barrel can produce a lot of extra drop clearance.

    I've seen a good many slides that were broken in the area noted. I asked a salty old armorer why that seemed to happen, and he pointed out the work and said simply: "Because some ****** idiot cut this away"...and pointed to it. Then he showed me a better way. It stuck.

    So...a note to all you aspiring pistolsmiths and general armorers.

    Always cut on the cheaper part, whenever possible. Study the problem to see if there's a better way. If you can get what you need by taking half off one part and half off another, that's better than taking it all from one. Leave the structural integrity of a part alone if possible, if you can get to where you need to go by another route, and...this is the one that took the longest to get through my skull...Before you cut, file, grind, or polish ANY-thing, determine if you're altering the correct area or changing the necessary dimension. Measure thrice...Cut once...Repeat.

    In this case...and Art may have done this, since he seems to have a good knowledge base...See if the barrel will drop father with the slide off the frame than it will with the slide and barrel are ON the frame. The frame bridge may be at the root of the problem instead of the radius in the slide. It's usually caused by the vertical installed height of the slide on the frame...and taking a bit out of the bridge...on radius...is part of the cure. .003 from the bridge, and .003 from the barrel's lower radius...and smoothing the lugs with an iron will provide another thousandth or so...All this stacks up for a total of .007 inch of additional clearance between the top of the barrel and the slide, and unless something's badly wrong...it's usually enough. .I consider .010 inch the minimum here, and prefer to see .012 to .015 inch...but I can live with .010 as long as the timing is right and the barrel drops fast enough.

    The lower lug may also be a player. Look to see if the feet are contacting their recess in the frame and holding the barrel off the frame. You'd be surprised at how often this happens, and how often it's overlooked.
    And remember that the barrel isn't actually supposed to contact the bridge...though most do without causing problems. It should stand off a thousandth or two...but no more. Tough to get this ideal, and it requires much skill and patience. Another thing to look at is whether the width of the lug is contacting at the sides and holding the barrel up. Seen that one a lot when using aftermarket barrels. Might want to look at the link pin too...If it's not dead flush on some lugs, it can interfere with the drop.

    Luck!
    Last edited by 1911Tuner; 15th November 2005 at 13:28.


  2. #2
    Join Date
    9th August 2005
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    >>>
    Let's look at the practice of modifying the slide in the noted area for the purpose of obtaining barrel drop clearance.
    >>>

    Huh? As a sticky, this intro doesn't give enough information to figure out what portion of the slide you are talking about. Or what original thread you were referring to.

  3. #3
    Join Date
    1st June 2004
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    Lexington, North Carolina...or
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    Area Fire

    >Let's look at the practice of modifying the slide in the noted area for the purpose of obtaining barrel drop clearance.<

    Sorry...I guess you got here late.

    At the rear in the part of the lside bore that stops the barrel's downward drop
    with the slide off the gun and the slide and barrel oriented in the full rearward
    position...as if it were at the end of the recoil part of the cycle. Some guns have the barrel drop limited by this part of the slide, but most aren't. The frame bridge/barrel bed is the limiting factor.

    All better now?

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