Custom Chambering a Barrel by High Speed Shooting Solutions

As a “gunsmith” I find it entirely amusing how often customers believe that there is some real secret to what we do. Most of the time it’s simply knowledge, and more importantly, a confidence to work on a specific firearm. In fact, it’s amazing how often I get a firearm in that I do not know much about (especially old revolvers).

One of those common tasks is chambering a barrel, which actually is a relatively simple (yet time consuming) task of running a chamber reamer into the barrel. Re-chambering or chambering is a simple operation, mechanically speaking. One sets up a barrel in a low-speed lathe and using a piloted reamer (which is NEEDED, if one is not using a pilot, the chances for error are huge), slowly pushes the reamer into the barrel, making sure to clean out the “chips” or metal shavings.

Production barrel manufacturers will typically use a different process using a “roughing” reamer to get the general shape before using a final “finish” reamer to provide the final shape of the chamber. Further, they will use CNC machines to set depth accurate within a few tenths.

High Speed Shooting Solutions breaks this down visually on a custom bolt-action barrel.

Nathan S

One of TFB’s resident Jarheads, Nathan now works within the firearms industry. A consecutive Marine rifle and pistol expert, he enjoys local 3-gun, NFA, gunsmithing, MSR’s, & high-speed gear. Nathan has traveled to over 30 countries working with US DoD & foreign MoDs.

The above post is my opinion and does not reflect the views of any company or organization.


  • aguywhoknows

    A CNC machine will cut your chamber correctly in a few hundrets, not tenths.

    • Eng

      A good CNC should be able to hold plus or minus eight thousandths on a depth easily (+/-0.008″). Thats +/-0.2mm for the rest of you.

      • M.M.D.C.

        I’ll see your eight thousandths and raise you ten thousandths.

      • Michael Lubrecht

        Are they really that sloppy? I figured the tolerances would be in hundredths, not tenths. I try to hold +/- 0.002″ on my modest-quality Jet lathe.

        • MR

          Tenths…of thousandths (0.0001″). As mentioned above. Someone working with those tolerances can get used to their unit of measurement, and forget that the rest of the world think a tenth equals 0.1″.

      • Paladin

        A good CNC machine should be able to do a fair sight better than that. Hell, a half decent machinist on a manual lathe should be able to do better than that.

  • NCJohn

    Anyone with basic machining skills and the appropriate tooling can chamber a barrel, as pointed out it’s not hard. The difference between a skilled machinist or a “parts changer” and a gunsmith is the knowledge of how and why the parts work together and what to do to make them work better.

  • M.M.D.C.

    Not sure where I got it, but I have had then idea for a long time that the case swells and forms a seal in the chamber under pressure. Is there disagreement about this among gunsmiths?

  • mike

    Seems like having the steady rest set up on the threads would be very hard on the brass inserts and it would be better to have it set on the not threaded portion of the barrel.

    • Tom

      Assuming that non threaded part has been checked for concentricity with the bore

    • Paladin

      And I’m just sitting here wondering, “Why the hell wouldn’t you just set it up in a four jaw chuck and run the barrel through the spindle with a spider on the muzzle end to hold it steady?”. There’s no reason to work that far away from the chuck when all you’re doing is reaming.

  • Mark

    Tenths is machinist speak for 1/10000(0.0001). Or other words, a tenth of a thousand.

  • Anon

    Don’t know if its been done here yet, but I think a series of articles on starting gun smithing as a career could be nice. Give some reasons why or why you shouldn’t want to be one, talk about starting and or education, what being a smith actually is, etc etc. If anyone at tfb is equipped to do that.

  • Komrad

    that bit about the case adhesion holding the action together more than the lugs sounds very wrong to me, otherwise, why would they ever sell steel cased?

    • Michael Lubrecht

      Steel cased ammo does have less flexible side walls than brass, with less adhesion. It’s less likely to get a good seal on the chamber wall, and it actually does transmit more impulse back into the bolt face, but not catastrophically so. They also sell Teflon coated ammo (the cases that is) which seems entirely counterproductive to me.

      • Ben

        Teflon coated anything in the gun world is generally a gimmick.


    • SidViscous

      Is very wrong.

      Cut the back of case apart, calculate the cross sectional area of brass at the back of the case, compare that to the cross sectional area, and the thickness of the steel lugs. Which do you think has more strength. Remember, if those steel lugs were not holding that thing together (he says it has very little to do with it) if the case walls are holding the case in, the back of the case will see all of the pressure of the charge, minus what the bolt holds. If the bolt holds little, you really think the back of the case will hold the rest?

      And this guy should know that.

      Steel case is an issue because it allows for gasses to blow past. If you then shoot brass, there is more friction the case walls due to the rough surface and carbon schmutz, and when you go for extraction, the relatively small (compared to the bolt lugs) extractor rips the back of the case off, leaving the rest of the case in the chamber.

      So think about, the small amount of steel in your extractor can rip a case apart, yet that same exact part of the case is holding the gun together under firing, while the steel bolt lugs are doing “very little” in his words.

      From my research after about 35Kpsi the brass is in it’s plastic phase and is not holding anything together structurally. In Rifles the brass stiction has no effect, but the expansion and sealing does. To be fair his texturing doesn’t hurt anything really. But could lead to earlier case head separation if you let the chamber get dirty enough.

  • Cymond

    I have a barrel that I would like rechambered, but it cannot be put in a lathe. No joke, I have a Uberti reproduction of the Sharps Pepperbox.
    Any suggestions how that can be done, or what/who to look for as a gunsmith to do it?

    I’d like to have it rechambered to 22LR. Yes, I know that firing 22LR will damage the frame eventually, but I mainly want to so I can fire Aguila Colibri, and also “just because”.

    • Norman Kowalczyk

      Put the reamer in a mill, clamp the barrel down.

      It can be put in a lathe with a 4 jaw chuck, but that would be a PITA.