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Bits & Reamers

 Long Bit, Short Bit, and Breaching Bits


   These bits are used to bore, ream barrels and finish the breech area on barrels.  These are easily made by hand and all work admirably.  First off, we’ll start with the LONG BIT.  This is the reamer and is also called the armory bit.  Wallace Gussler, formerly in charge of Colonial Williamsburg, kindly provided instruction for this task many years ago, and I guess it’s only fair that I share this knowledge.  There certainly are other ways and means to make a reamer, but this is one method that most modern hobbyists can use, even if they don’t have access to a forge. Just click your mouse on the photographs to enlarge them.

The LONG BIT,   a.k.a. the ARMORY BIT

     The heart of the matter is a square file.  They come in several sizes and you’ll need to select one that is quite a bit smaller than your intended bore.  Example:  a 5/16″ square file will easily ream out a barrel to .50 caliber or a tad more.  The job will proceed much faster if the barrel is first bored out to within a few thousandths of an inch under the desired bore size. 

A typical square or “four square” file.

     After selecting the file, heat the file to a bright fire house or cherry red color.  Do not quench.  Allow it to cool in wood ashes or sand slowly so that it is as soft as you can get it.  The teeth are then ground off and the sides watched closely so they stay square and flat.  Waviness is not wanted!  If waves do occur, simply stone the sides until the surface is as you desire it to be.  Leave the tapered tip on the file as it provides some lead which helps prevent the finished reamer from getting stuck inside the bore.  Grind or file a notch near the tip of the file.  This is where the wooden spacer or “shoe” gets tied in place.

The teeth have been ground off, sides squared up flat, corners sharp, and the notch ground in place.

The wooden shoe is now shaped and tied onto the long bit with common string.

     The file’s tang is then scarf welded to an 8″- 10″ length of hot rolled round rod.  This rod is scarfed at both ends.  Forge welded or arc welded, no matter.  The file needs to be straight and in line with the rod when finished.  Any excess weld is removed from the file/rod and none is allowed to protrude past the edges or corners of the file.  If one side of the file sticks out from the center of the rod because the file was not welded on center line, no problem.  This side automatically gets to be the bottom flat of the reamer that the shoe rests against.  After you have ascertained that the file and rod are as straight as you can make it, go back and stone the sides of the reamer until the edges are sharp and square.  “Sharp” is essential at this point.  If your edges are sharp, they will cut regardless of the direction of rotation of the bit!

     Now, reheat the file to that cherry red and quench in old, used motor oil.  Keep it moving while it’s cooling off.  If your quench tank is deep, hold the file straight up and down in the oil.  If it is a shallow tank, hold the file horizontally in the oil. Many of the old timers, and myself included, would align their shallow quench tanks with magnetic North.  This was to prevent warping during the quench.  I have quenched aligned North and at some other direction and I have to say the reamers have always come out straighter when the tank points to mag North.  Some of you will say b-ll sh-t!  No matter.  Just get your tool straight as can be.  If it warps, reheat, tweak, and then reharden until you get it correct.  Next,  stick the reamer into the wife’s oven, AFTER, I repeat, AFTER you clean it up.  Run the oven up to around 450-460 degrees for about an hour to draw the temper.  If you temper at the forge, draw her up to a yellow straw color.

     After you’ve cleaned up the bit, weld the shaft to another hot rolled steel round rod of the same diameter.  This second rod needs to be so long that when it’s welded to the bit, the entire bit is then long enough to allow 95% of the reamer portion to protrude out the barrel at the end of the stroke.

     To make the shoe, take a piece of ramrod that is as wide as, and as long as the reamer bit itself, and saw it down the center.  Lay the flat portion against the bit and trace the outline of the bit onto the wood.  Remove the wood outside of the lines and file a notch in the wood that corresponds with the groove in the reamer bit.  Taper the rear end of the shoe to give some needed lead for the leather keeper.  The shoe needs to be thin enough that when it is mounted to the file, the entire long bit just slides into the barrel.  Remove excess thickness from the flat side of the shoe.  Leave the rounded side round!

     The leather keeper is just a washer made out of some belt thickness leather.  The hole is drilled large enough that the reamer and attached shoe just slide through.  The spacing shims are made from brown grocery sacks or shipping/mailing paper.  Make a couple of dozen before you start to ream your barrel.  Peanut oil as lubricant works great, as does used motor oil, hog lard, sweet or olive oil, but avoid old bacon grease or used cooking fat.  It has salt in it.  You can use it if that’s all you have, but remember to clean the barrel well when you’re finished or rust will start quickly.

Really a precision made keeper, eh?  It’s real mule hide and’ll wear like iron.

All the components assembled.  She’s ready to mount an’ git to work!

     In use, the reamer is first passed through the barrel to make sure it will fit easy.  Then shims are daubed with oil and placed between the shoe and the bit.  This expands the reamer so that it just contacts the bore’s walls.  This oil holds the shims in place better. Don’t shim too heavily or thick as you want the bit to cut, but still pass through the bore, easily. The keeper is then slid over the end of the shoe to hold the shimmed shoe against the bit.  The tapered end of the bit is just started into the bore and the bit is then lubricated.  The bit is spun and passed through the bore, barring complications, non-stop.  The leather keeper slides off the reamer head in a rearwards direction as the bit moves farther into the bore. 

     Only the two corners of the top flat should do the cutting.  At the end of the stroke, the swarf or grind dust on the bit is brushed off and the bit, still spinning, returned through the bore.  As the long bit backs out the bore, the keeper is then slid back onto the shoe and reamer head to prevent the shims from becoming dislodged and falling out.  You’ll only forget a couple of times and it’ll become second nature.  The bit is then cleaned again and another shim is added.  This continues until you reach the desired bore diameter.  Now, if I forgot something, I apologize.  Hopefully, the photos will help get you through the process.  There’s a lot running through my mind trying to keep this a KISS page.  For those of you who do not know what KISS means, it just says: Keep It Simple, Stupid!

The long bit entering ol’ Don’s barrel. 

Adding brown paper shims to the long bit.  Note the shim has had oil applied on both sides.

SWARF!  This is what was removed on the return stroke, so you can see that the bit works in both directions and why both top corners must be sharp.


Swarf again.  Looks like the blazes, but it’s your guarantee that all your hard work is paying off.

Dead nuts on the money!! 

23 “papers” added!  (Papers is a smithy term meaning shims for a reamer or rifling head.)

VIOLA!!  Slick, shiny, and lookin’ like a million dollars!  The finished bore is now ready to be rifled.  FYI: it took about 2 and one quarter hours to ream the bore from .485 to a flat .500.  We even had time to stand around and shoot th’ breeze, too.


This is the work horse called the Short Bit.  It drills or bores out a barrel.  It is much shorter and stubby than the Long Bit.  These can be made from square files, a length of tool steel, or a piece of tine from a farmer’s hay rake. Using a piece of tool steel or rake tine, scarf the metal to a piece of hot rolled steel rod.  Draw the bit out square and with a taper towards the forward end of the bit.  File it smooth and sharpen the corners well.  Heat the bit to red hot and twist.  The twist can be any direction, but remember that the bit will only cut well in one direction and remove the chips.  The opposite direction will cause the bit to jam up.  Make certain the bit is straight.  Now harden and temper to a brownish straw color, or if the bit and rod are short enough, put it in the Wife’s oven for an hour at about 375 to 400 degrees for about an hour.  It normally takes several different size short bits to bore out a barrel and do expect to have them break on you.  That is just a fact of life.  Here is a photo that shows an unformed piece of tool steel on a rod and the finished bit.

Specialty bits to enlarge the bore of barrels that have already been rifled

     The top bit is generally used to make a smooth bore whilst the bottom bit has a pilot to fit the bore to help it run true.  You will notice that the bits are held in place with set screws that have been filed very short for good clearance.  The rod is sectional and held together the same way .  The following photo is a close up of the pilot that was ground onto the end of a common machinist bit.

Breeching Bit

    NOTE!  This bit is NOT used to drill the breech plug hole in a barrel.  It is used to properly complete that hole.  This bit performs the same function that an end mill would do if the barrel were mounted in a lathe.  It is made from tool steel that has been hardened and tempered after completion as described above. 

     The completed drill bit.   A pilot was formed on the end to keep the bit centered.  It has two cutting surfaces on the sides which were made with a mill. These cutting surfaces flatten or square up the bottom of the hole as left by the machinist bit used to drill the initial hole.  This allows the breech plug to butt up against the bottom of the hole and provide a good seal.. The sides were angled back for chip clearance.  The wide portion is the stop collar that controls the overall depth of the hole.  The lower portion is the shaft that fits into your E-lectric drill.

The next photo shows the top of the pilot and the cutting edges of the bit.

Concerning my methods:  You got questions, I got answers.