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Thread: Barrel Chamber Misunderstandings

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  1. #1

    Barrel Chamber Misunderstandings

    It seems to me that there is a bit of a misunderstanding about what the chamber on a 1911 style pistol should be like. Over the past several years I have personally examined dozens of pistols with barrels that have been “professionally” installed by “competent” pistolsmiths. Without exception, all the barrels inspected had the same sort of issues. Below is a short evaluation of some of what I have seen and my opinion on the way a chamber should be done based both on personal experience and how I was taught.

    First of all it seems that none of the smiths that installed barrels that I have seen realize the chamber that is cut in the barrel when you receive it from Kart, Bar-Sto, KKM, or whomever, is not finish reamed. With very few exceptions, most barrels, whether in a semi-custom gun from any number of makers to full house custom pistols from the most famous of smiths, have not had this most basic of steps completed.

    Finish reaming the chamber is a simple action that can be accomplished by even a neophyte with a small bit of training and any number of manufacturers’ reamers. The two I recommend are Manson and Clymer. All that needs to be known is the depth of cut you desire from the back of the finished hood. On a .45acp, for example, it should be .905 to .908”, using good calibrated calipers, from the above mentioned hood area. Of course this is based on having a hood to breech face gap of just less than .001”. This will help make for good accuracy and reliability.

    Perhaps most smiths don’t realize the chambers are not cut. It is very easy to tell if one has been done or not. For example, every Kart barrel I have fit has a bump in the chamber from the factory. It is apparently part of their barrel making process that leaves a slight raised area in the chamber. The bump is not a problem unless it is not removed. If left as is, I believe it can cause broken extractors, failures to feed and eject, not to mention accuracy suffers greatly.

    Second, there has not been a single chamber I have examined that has been polished. Perhaps people actually believe that the lubricity traits of brass mean you don’t have to polish the corn cob rough chambers that come from most barrel makers. Or perhaps they think that after a couple thousand rounds the chamber will self polish. In either case they are, in my opinion, incorrect. I can totally understand a $500.00 bone stock pistol being this way, but a gun running from $1000.00 and up should be smooth and shiny in the chamber.

    Finally, regarding 1911 barrel chambers is the throat area. Perhaps the second most misunderstood area of the barrel is the tiny ramp like space that leads the bullet into the chamber. Many people apparently fancy themselves as jewelers and feel the throat should be covered with as many facets as they can cut into such a tiny area with a dremel tool. Others seem to think the rougher it is the better it will function. Still others insist on over cutting it, rendering the barrel dangerous and useless, or making it so convex in shape that you couldn’t feed a round if your life depended on it, as well it may.

    The reality of the throat area is that in my opinion and experience, for the best in reliable feeding, this area should be slightly concave, not convex, in shape. It should also have neither rough spots nor facets. This is not a diamond, it is a pistol barrel. Furthermore, along with the aforementioned chamber, it should be polished to a mirror finish. The top edge of it should be SLIGHTLY rolled over into the chamber for those reloaders who like the short bullets. And unlike some barrel makers believe, it should never be rounded under on the bottom edge where the barrel meets the frame, but rather sharp and smooth.

    Of course I could go on and on about the nuances and minutia of barrel chambers, crowning, leg fit, hood gap, etc, but I don't want to bore you with all the details that fitting a barrel correctly entails as we would be here for days. I simply wanted to point out something that I see on a regular basis that could easily be corrected with a bit of care and instruction.

    Sincerely,
    Joe Chambers

  2. #2
    Join Date
    25th September 2006
    Location
    South of Lake Superior
    Posts
    13,056
    Hi Joe:

    Thanx for sharing your observations with us. They are both welcomed and appreciated.

    I was especially interested in your comments regarding the barrel throat (ramp) leading into the chamber. The various vintages of Ordnance barrel drawings I have reveal an interesting progression over the years:

    • ~ 1940: Convex ramp with 0.310R + 0.005 inch radius.
    • ~ 1960/70: Same earlier convex ramp or a straight "Alternate Chamber Ramp".
    • ~ 1980: Only the straight chamber ramp (no provision for a convex ramp)

    Interesting because Army Ordnance seems to have phased out the convex ramp and you favor a slightly concave ramp. Interesting indeed!

    Best Regards
    When you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind. [Lord Kelvin]

  3. #3
    I use a Clymer finish reamer. The biggest advantage I see it that is that it tapers the lans in the barrel throat. Obviously, it also lets you adjust headspace. To measure headspace, I use a "GO" gauge and feeler gauges to measure to the breachface.

    I'm curious, how do you polish your chambers?

  4. #4
    Tom,

    I use a dremel with a felt wheel and polishing compounds that we get that are used in the jewelry industry for polishing metals. This compound does not have inert ingredients in it to mess up your bluing like many you purchase.

    I also use feeler gauges to measure the hood to breach face gap when the slide is not on the frame, but use calipers to measure the depth of the chamber as I'm cutting it as this seems to be more accurate than "Go" gauges.

    Sincerely,
    Joe Chambers

  5. #5
    Join Date
    1st June 2004
    Location
    Vatican City
    Posts
    15,170
    Excellent post Joe.

    Do you have any pictures of the gun/guns you submitted to join the APG?
    "The pistol, learn it well, carry it always ..." - Jeff Cooper

  6. #6
    Join Date
    24th August 2007
    Location
    Crystal Springs, Ms
    Posts
    675
    Many thanks Joe,

    As a student of 1911's about to finish my first build, I'm very much in need of all the instruction I can get. I've read about polishing rifle chambers but now I know my 1911 chambers need to be polished. I'll add that to my list of task to do on my build.

    Also, one of these days could you give us an in depth explanation of barrel fitting? Perhaps in installments if one continuous explanation would be to long? It would be very much appreciated.

    Randy
    (alias Toolman - that reffers to carpentry, woodworking, etc. not 1911's)
    Last edited by toolman; 3rd February 2010 at 08:32.


  7. #7
    I will post some pics of the guild guns and other guns as time permits, and as I figure out how! LOL!

    As for the barrel fitting lesson(s), I will also work on doing that for those interested either on here or in some other format. I could write volumes about fitting barrels and things I've seen done to them as well as the other parts of the pistol. But I won't bore you with all the tediousness of that right now. Needless to say there are a lot of details that make a .45acp consistently put 10 shots at 50 yards into less than 1.5" groups. (My average over the past three years with the .45 has been 1.37" and with the 9mm just under 1".) But I also have to give credit where it is due.

    I have spent the last three years of my semi-short life sitting three feet away from an accuracy/reliability guru named Bob Marvel. He taught, I listened, questioned and experimented, sometimes for as many as 100+ hours a week for months and that is no exaggeration. Now, he is very humble and will tell you I have incredible drive and skill, and I will tell you yes that is true but, without proper instruction all you have with those two things is a fast smashed up race car. ;-) He taught me how to do what it is I do.

    And toolman, I'm glad you clarified that! LOL! :-)

    Sincerely,
    Joe Chambers

  8. #8
    Join Date
    26th February 2007
    Location
    Wagoner Co, USA
    Posts
    1,196
    Hi Joe, I also find your post interesting and informative. The pistols my son and I build are for our own use so we only have to please ourselves...sometimes difficult by the way. We have used Nowlin barrels till our first Kart barrel recently. Always used a Nowlin reamer because it was suggested to us that we do so. I was told Nowling barrels are different thus the need for the Nowlin reamer. Hey, I don't know the differrence but the pistols work so I guess the difference really does not matter. The Kart barrel is really nice and has been reamed with the Nowlin reamer...pistol works fine. We agree about cutting the the throat area of the barrel...not a good idea! My son thoats all of his barrels; I do not throat mine unless the rounds don't feed well. Neither of us has ever polished a chamber. May do it some day as it sounds like a neat value added option. Good luck with all your work and thanks for the info.

  9. #9
    Join Date
    25th September 2006
    Location
    South of Lake Superior
    Posts
    13,056
    Hi Joe:

    For years I've been hearing (on this forum) about handloaded ammunition feeding problems with Kimber 1911's being due to "tight chambered Kimbers". It's almost as if when a Kimber chokes on a handload the automatic fix is more crimp. I don't have a Kimber or even access to one for measurement purposes, so was wondering:

    • Any idea if chambers in Kimber barrels are really tighter than others?

    • If so, what's "tight" (knowing the SAAMI minimum ID at the stop shoulder is 0.474" for the 45 Auto/ACP)?

    • Or is the "tight chambered Kimber" just one of those urban myths that never seems to die here in cyberspace?

    Regards
    When you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind. [Lord Kelvin]
    Last edited by niemi24s; 3rd February 2010 at 17:46.


  10. #10
    Join Date
    1st June 2004
    Location
    Lexington, North Carolina...or
    Posts
    11,207
    The bump in the top of the Kart chamber is from the letters being stamped. I can't account for the other bumps I've seen in their barrels recently...but I agree that they all need to be finish reamed. If for no other reason than to cut a proper leade. Kart's is too short and too abrupt.

    Concave barrel ramp. Indeed! The barrel ramp is a clearance...not a feedway or bullet guide. That's why they were widened for SWC bullets...to provide that clearance for the bullet shoulders.

    Overcut ramps that compromise head support? Absolutely. Seen it done in some pretty expensive semi-customs from some respected shops. Even seen it in full-blown customs...just not as prevalent. I most often find it either in pistols that don't have the correct feed ramp angle and geometry, and the "smith" starts cutting on the barrel ramp in order to relieve the 3-Point Jam that results from the bullet nose being directed straight into the barrel ramp, or...Dremel Dan has decided to remove the step between the top of the feed ramp and the lower edge of the barrel ramp and blend them smoothly together so the gun'll feed better, by gawd...and in so doing destroys even a proper ramp geometry. So, he attacks the barrel ramp in order to let the bullet nose skid across the top instead of hitting the center of the ramp. It does feed...but it also very often bulges or even blows cases.

    I also like to see a little headspace and a small clearance between the hood and breechface. I like .003 inch there, but that's just me.

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