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Thread: Clinic-3: BFC

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  1. #1
    Join Date
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    Clinic-3: BFC

    Barrel Fittically Correct.( In case anybody was wonderin'.)

    Note:

    Although I wracked my brain in the effort to remember all the details of this saga as best I could, some of the dimensions and procedures given may not be entirely accurate...but they're close. After nearly 40 years, the little things tend to get a bit fuzzy.
    ************************************************** ***

    I arrived at the shop two weeks after I started on my journey to truth and wisdom, a wiser but apprehensive lad. Having learned my lessons via the long, hard route...I was duly chastised, and today was the day that I would do this barrel thing for keeps. It was a brightening, nearly sunny Saturday morning...0500 hours. Henry figured that I'd need to get an early start. He was right.

    Uncle H opened a package that contained a match-grade barrel, still covered with the odd-smelling oil that had been there for many years. Void of proof marks, this wasn't a Schuemann or a Kart or a Storm Lake. This one would be worth mucho dinero if it hadn't been opened that Saturday.

    All critical dimensions were oversized for hand-fitting...and the chamber was semi-finished.
    Short reamed by .015 inch so that the final headspace could be chosen by the armorer. A true hard-fit barrel. I was scared.

    The first step was to gauge the slide for lug locations and record them. The measurements were done 3 times, and an average of the three taken for a final fit dimension. Likewise for the barrel, from hood to front lug faces. This barrel was to be fitted to pistol #2...since the first barrel was dead in the water. It was a 1944 production Remington Rand.

    Henry told me that the process would be a bit different this time, since the second thrust face in the slide was located a bit too far to the rear. I wouldn't start with the hood this time. I would start with the #2 barrel lug.

    Checking the final measurements determined that I would have to cut the face of the #2 barrel lug back by about .003 inch in order to bring #1 into contact. This cut must be made straight and true, and no more than .0005 inch out of square. That's a half-thousandth of an inch. If you had a sheet of steel that thin, you could probably read through it. It was to be one stroke of the file and measure...repeat, until the dimension was reached.

    Lug #1 was within reach...On to lug #3. That one was now almost .005 inch off the slide's abutment. Too far for proof equalzing. Time to cut the faces of lugs 1 and 2 by enough to
    bring #3 into play, or at least close enough to equalize it by proof-firing...which is a maximum of .002 inch. This meant that the static headspace would be increased by .008 inch by the time all lugs were equalized, leaving .007 inch at most to finish, depending on how close I could get it
    in the initial fit. A sheet of 20-bond typing paper is barely more than .004 in thickness, so I'd have to be deft with the reamer. The fact that it was spankin' new would make the job easier, but because it was so sharp, just a little too much pressure
    would cut farther than Henry wanted me to. Initial static headspace was to be set at .895 inch...or .003 inch under minimum.

    It took me 6 hours to get the lugs into contact. #2 was solid. The others were lightly kissing,
    allowing just a little for final equalizing. Now to the hood. it had to be carefully cut...by hand...to allow the sides to enter the recess with just a bit of light contact. Final adjustment to be made after the length was set. Length was to be cut so that the barrel would enter the slide with medium thumb pressure. A square was used to check the lateral misalignment, and adjustment made on one side of the hood. Final clearance was just .002 inch per side with a light interference fit at the breechface. Static headspace checked with a special short GO gauge and a strip of paper suggested an approximate dimension of .890 inch. I wanted to go home, but I had to stay with it, if I had to stay until midnight.

    On to the lower lug and the test fit into battery. There were no handy lug cutting tools...just a round file, a scrape made from a lathe bit...and my trembling hands. The round file was used in a draw-file motion, pulling it sideways on the lug to shorten and blend with the rear radius.
    The scrape was used for fine adjustment after trial fitting. The gun finally went into battery with hard pressure on the back. The slide was just barely rearward of the frame. The disconnector reset as per design, but the thumb safety notch was a little shy of perfect alignment. Vertical lockup was tight, to say the least.

    Out came a ground and hardened .196 rod and the lapping compound. The rod had a T-handle
    brazed to one end. Another identical rod with a .198 diameter was also on the bench...in case we needed it...and the lapping began. I moved the slide forward and inserted the rod through the slidestop pin hole...and let it go under recoil spring pressure...and turned the rod to walk the slide forward. Reapplying the compound on every other pass, I got the slide to battery
    about the time my hand felt like IT was locking up.

    He handed me a slidestop. The slide refused to go smoothly, and we turned to the .198 rod for the final fit. It didn't go much faster than the initial fit because after every pass, I had to take the gun apart...rinse out all the compound...and try the slidestop. When the slide finally went to battery on the slidestop...just a wee bit tight...lapping compound was again applied to the
    stop crosspin, and the slide hand-cycled about 5 times. Perfect!

    Whoops! A problem with the barrel to slide clearance in full linkdown emerges...The clearance is good at .015 inch...but it occurs at .300 inch of slide travel instead of .250 inch. OMG!
    Not a biggie, sez Uncle Henry. The barrel is stopping on the vertical impact surface like it should. The problem is at the front radius of the lower lug. It's not letting the barrel drop fast enough. Reshape it to reduce the sizeof the radius...elongate the top of the link hole just a bit,
    (Seems like it required .002 inch) and you're probably good to go. Turned out that he was right. Imagine THAT!

    Lug equalizing was done under pressure with handloaded rounds with cases measured to
    insure that the gun would go to full battery. Three rounds later, we returned to the bench and
    looked things over. The short GO gauge was inserted...but this time the strip of paper slipped out from between the gauge and the slide without tearing. Headspace was estimated at
    .894 inch. The lugs had seated and increased the static headspace, and this about was as far as it would go. Time to decide. Was I building the gun for maximum accuracy...or was maximum reliability my goal? I opted for reliability. Henry was a little disappointed, but let me go with that. He said that I'd need to open up the hood clearance another thousandth or two per side. Okay then...Remember to cut a bevel on the underside of the hood. Yessir.

    He attached a stop collar onto the reamer and reminded me of the "Rule of Halves." I placed the reamer into the chamber and pushed it into contact with the shoulder... and slid the collar
    lightly against the chamber hood. The reamer had a little light interference in the forward (approximately) 32nd inch of the chamber, and he told me to turn it once slowly to remove the taper...then bring the reamer out and clean the chips off. The second pass still suggested there was still a little taper, and the process repeated. The third pass put the reamer into solid contact with the shoulder. I slipped the collar back into contact with the face of the hood...under its own weight only...and locked it down. With light forward pressure on the tap handle, I turned the reamer once...backed it out...cleaned the chamber, and checked the headspace with a standard .898 GO gauge. Almost! Cleaned the reamer again and
    reset the stop collar. NOT...quite! A tick more. DAMMIT! Too much! Henry reckoned that my final static headspace was .900 inch. Firing the gun a few hundred rounds would probably open that up by maybe another thousandth as the lugs settled in and took a final, solid seat. The barrel was now not only precisely fitted to the gun...it would likely wear completely out before the headspace would increase to the point of causing a problem. The locked breech pistol was now as strong as the design would allow. The light "seating" flange was dressed off the lugs with a stone. (Lookin' good, just like Hollywood!)

    The bushing fit was straightforward, done pretty much like any other match bushing with just the tiniest bit of interference as the barrel approached final lock without springing or producing any linkdown problems. That part I was able to do without coaching, and the gun was wicked accurate. I actually wound up fitting a second, looser bushing to the gun for reliability...but I don't think it was ever used. I'm still tryin' to buy the gun from my cousin...but he's a tough nut to crack. It'll still part your hair at 25 paces. I shot it about 3 years ago. Cuzzin refuses to sell, but will trade for my Union Switch...NOT!
    Last edited by 1911Tuner; 22nd November 2005 at 10:48.


  2. #2
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    I cannot believe you can remember those numbers.
    It is amazing. Now I need to learn how to fit a barrel.

    When are you going to give an online class?
    Because I hit what I aim at, that's why.

  3. #3
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    Numbers

    Quote Originally Posted by AnthonyRSS
    I cannot believe you can remember those numbers.
    It is amazing. Now I need to learn how to fit a barrel.

    When are you going to give an online class?

    LOL...I probably didn't remember'em exactly. Like I said...it's been a while. I wrote'em down as nearly as I could remember after a lot of rememberin'...so they'll be pretty close.

    Online class? Ain't gonna happen, mah fren. It's more a logical, common sense approach anyway. Nothin' voodoo or black magic. Practice on a junk barrel with a file until you can cut straight, and fill up on patience before ya start. You can get the hood tig-welded on the cheap. The slide gauges are the tough part to arrange. High-dollar to buy, and tricky to make. Mine are home-cobbled, and butt-ugly, but they do the trick.

    Figure out which lug will hit first, and go from there.

  4. #4
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    Hark!

    That sound! Could it be wheels turnin'? Will Brownells sell many square pillar files in the near future?

  5. #5
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    I'll go for it one day. When I have more disposable income and can buy the right tools- it always makes things easier. Right now I've got a Nork I'm finishing up...Kinda wish I'd left it alone. If this trigger job turns out swell, I'll post pictures after I park it.

    I never could leave well enough alone.
    Because I hit what I aim at, that's why.

  6. #6
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    Well then...

    No mo' qestions...I guess either everybody's clear on it...completely confused...or figgers that I'm fulla sheep dip and just don't wanna say so.

    Just a sidenote...

    Many smiths feel that horizontal engagement on the first lug is adequate, and...assuming that they get full vertical depth...it is. It won't maintain specs as long as with all three lugs sharing the load, but it'll do for a quick and easy barrel upgrade. I've used the Kart Easy-Fit system in two guns with good results, but the guns aren't destined for hard use...so it'll do.
    The question is: Are you satisfied with "adequate" or do you want it right?

    Equal engagement is how the gun was designed to work because it provides
    full strength and rigidity in the lockup. The 1911's radial lugs are fairly small,
    and don't provide a lot of surface area to bear the shock and stress of
    hard use in the long term before deformation sets in...with the resulting increase in live headspace...and the higher the pressure from the ammo, the faster this happens. Correctly fitted, the rifling will be worn nearly smooth well before headspace opens up enough to cause a problem...so long-term durability is the main advantage of equalized lugs. Accuracy can be had with just one, provided everything else is well-fitted.

    The drawback with the one lug system is in knowing WHICH lug is bearing the brunt. Since you can't actually see which one it is, you have to use the gauges to find out. Even on the first lug, it's impossible to tell because even though it's where you can see it, the slide abutment face is under a short projection on the slide...and if another one is actually taking the thrust, and #1 is only 2-3 thousandths off...it may LOOK like it's engaged, when it's not.

    A wise pistol wrench (Metalsmith) said it best:

    "I only know what I can measure."

    Words to remember when approaching a barrel fit, regardless of which method you choose.

    Luck! ...and happy Turkey Day to all!

  7. #7
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    No mo' qestions...I guess either everybody's clear on it...completely confused...or figgers that I'm fulla sheep dip and just don't wanna say so.
    I'm sure I'll have plenty of questions once I get time to fully digest it. I'm working my tail off today so that I can have the long weekend off.
    "The 1911 was the design, given by God to us through John M. Browning, that represents the epitome of what a killing tool needs to be. It was true in 1911 and it's true now." - Col. Robert Coates commanding, U.S. Marine Corp Special Operations Command Detachment 1 (DET 1)

  8. #8
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    First post on this forum and great job.

    1911Tuner has helped me with bbl problems on another forum, so his advice(teaching) is always good, as you already knew.

    IMHO, with shooting a fair amount of rounds through 2 Colts, I would say 80% of my "problems"/breakage is caused by improper bbl fit.
    None of it surfaced prior to 8,000 rounds I believe, but frustrating and expensive repairs.

    After re-reading this post, I wonder how, "in the good old days", how much time it took the craftmans/gunsmiths that worked for Colt to fit the bbl. Could they do it that fast, so that it would last...or is it possible that most shooters in that day, didn't shoot enough rounds to really test the long term fitting of a bbl?

    Regardless, it does pay to have it fit right in todys world.

    I thought with all this fancy, high tech CNC machines, etc, etc they could do a better job with bbl fit. Maybe, I had two "Monday" guns or the wrong brand...don't know.

    Thanks and Happy Thanksgiving.

  9. #9
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    Days of Yore

    T'was asked:

    >>After re-reading this post, I wonder how, "in the good old days", how much time it took the craftmans/gunsmiths that worked for Colt to fit the bbl.<<
    ********************

    In the old days, barrel steel wasn't as hard as the newer stuff they make'em out of today. The higher degree of malleability gave a little more leeway in proof equalizing, so the initial fit didn't have to be quite as precise. Since the headspace tolerance is so wide on the 1911, all the armorer had to do was make sure that the slide would go to battery on a GO gauge, and fail to close on a NO-GO after equalizing. (and dress the light flanging on the lugs that resulted from the process.) As long as it passed that test, the gun was good to go, and it was out the door.

    The above outline describes precise fitting of a barrel, and the tolerances are held much closer than an ordnance-spec gun. Unless your goal is wringing all the accuracy out of the gun that you can, you don't need to get quite that
    picky. If the lugs equalize, and the headspace is within the .022 inch window, the fit is good. Even if you're only able to get two lugs bearing
    equally, you're ahead of most factory-installed barrels..which are essentially drop-ins, and only occasionally have more than one lug in the fight...and only rarely is it the strongest one. If you can bring lugs 2 and 3 to bear and leave #1 kissin' air, it's still at least as strong as #1 alone..and probably stronger, assuming good vertical fit. If you can get 90% depth, along with #1 and one of the others...and maintain mid-spec headspace...you've got a barrel that'll likely go in excess of 50,000 rounds before needing attention.

  10. #10
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    I have a question, that I die to ask:

    I can understand the load bearing nature of the lugs. But what about the barrel's hood? Let's say that we have a pistol where the lugs are fitted properly, i.e. making contact as they should. Also, since this is the ... perfect pistol, when the barrel is locked in the slide (fully forward position), the barrel's hood is also touching the breechface.

    So, now as the slide/barrel combo starts to recoil, ins't the barrel hood participating in sharing the load of the thrust? Until the barrel starts unlocking, I think it is.

    Come on Johnny, enlighten me.
    John Caradimas SV1CEC
    The M1911 Pistols Organization
    http://www.m1911.org

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