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Barrel Crowning and Front Sight Installation
MikeG on 2013-11-08

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Front Sight Installation and Barrel Crowning



This tech note will cover two closely related gunsmithing projects, front sight installation and barrel crowning.  Although the sight installation project uses sophisticated tools that the average shooter may not have, barrel crowning can be done at home with very basic tools.

The subject of the note is an old surplus Turk mauser, cheap but functional.  After safety considerations, the most important part of working on guns at home is using something that would not be a great financial loss if it was ruined!  This old military surplus rifle fits the bill.

A new front sight was desired for two reasons.  First, the old front sight was tiny, pointed, and devoid of bluing - basically impossible to see in all but perfect conditions.  Second, the as-issued barrel length of over 29 inches makes the rifle cumbersome to handle in the field, as well as a pain to fit into the gun safe.  So, the plan is to reduce barrel length to about 26 inches, and cut a new front sight dovetail.

A standard sight dovetail is 60 degrees on a side, 3/8" of an inch wide at the bottom, and 0.100" deep.  There are special cutters for this, not surprisingly known as 60 degree 3/8" dovetail cutters!  This operation is best performed in a milling machine.  First, align the barrel horizontally and vertically in the vise.  Note the strips of leather padding the vise jaws, the replacement front sight perched on the barrel to the right of the cutter, and the angle finder with a magnetic base to the left of the mill.  The angle finder can first be put on the bottom of the action (where it's flat), and then on top of the barrel, for alignment.  This level of precision should be sufficient.

Rather than just trying to cut the dovetail with one pass of the special cutter, it is a good idea to 'hog out' the majority of the metal with a sturdy, inexpensive end mill.  A quarter-inch end mill is correct for this job.  The picture shows a technique of locating the cutter relative to the top of the barrel.  A piece of paper is put on the barrel, and the cutter lowered until it just shaves away the paper, which is about 0.003" thick.

Now, several passes are made with the cutter, about 0.020" at a time, until the depth of the notch is 0.095."  Recall that the front sight requires a 0.100" deep dovetail; the dovetail cutter will 'clean up' the bottom of the slot when it cuts the rest.  The toothbrush is used to apply some cutting oil between each pass, making a smoother cut and extending the life of the cutter.  It should also be noted that we'd certainly want to ensure that the barrel is thick enough for this cut, before starting!  The diameter of this barrel is about 0.700" here, and with a groove diameter of 0.323," this leaves a wall thickness of just under 0.190," plenty of metal remaining for this part of the barrel.

The dovetail cutter is now installed, and the cutter located with the same technique as used with the end mill, a piece of paper on top of the barrel.  After establishing the starting point, table is moved back from the cutter, then the cutter is lowered a full 0.100" and the cut is made in a slow, careful pass by bringing the table forward.

That's it!  Clean up the chips; the sight should barely start by hand; finish tapping it in with a brass punch.  Should it be too tight to start, the table could be moved 0.001" either left or right and the slot widened; if it was too loose, then the bottom of the slot will have to be dimpled with a punch to roughen it.  The Ashley Outdoors (now XS Sight Systems) front sight can be clearly seen compared to the tiny original front sight.

A word about front sight height.... a taller-than-necessary front sight, which can be filed down as needed, is probably the best way to go.  The gun has been fired with the original sights, which were found to regulate acceptably with the rear sight in the lowest setting.  So, the 'next' taller front sight was selected.  Note that replacement sights may be measured from the bottom of the dovetail, if you forget this, then you'll order a sight that's 0.100" too short (ask me how I know this).  If a fiber-optic or other not-easily-modified sight is desired, some careful measuring of the original sight, and analysis of point of impact downrange with the desired ammunition, should be performed first.  Remember also that if the sight is moved farther back on the barrel, the diameter of the barrel normally increases and this would raise the sight over the bore.

Now... as unique as 'dual front sights' on a rifle might be (ultimate in backup systems?), the original front sight needs to go!  This is the part of the tech note were we move from 'high-tech' to decidedly 'low tech!'  First tool is a hacksaw, with the barrel held in a sturdy bench vise.  As the end of the barrel is scrap, the vise jaws aren't even padded.  The vise jaws make a handy guide; leave a bit of extra metal on the end of the barrel, for later cleanup.

Done!  Cut is perhaps a bit rough as compared to a factory-new rifle crown, though.  Red paint is from the hacksaw blade.  Note... these barrels are hard!

Some quick cleanup with a file, or in this case, a bench grinder, improves things quite a bit, and squares up the end of the barrel for the next step.

Run a patch through the barrel (from the breech of course) to push out the grit, shavings, burrs, and other assorted filth out before the next step.  Now, what we need is a tool to square up the end of the barrel.  There is a cheap and remarkably effective tool available for this, which can be turned by hand, or in a drill.... the Lee case trimming tool!  Use the largest size possible that will just fit into the bore; in this case, a .30-30 is perfect. If the tool is a loose fit, wrap it with aluminum muffler tape to bring it up to size.  Chuck in a half-inch drill,or turn by hand if necessary.  A squirt of WD-40 down the bore, and some cutting oil on the face of the crown, and this operation is over in just a few seconds.

The crown will be recessed if the barrel diameter is larger than the diameter of the tool.... you've just created a fancy protected 'target' crown!  It will be necessary to clean up the burr that forms right at the edge of the crown and the rifling.  Many different techniques have been suggested, perhaps the classic approach is a brass lap and some valve-grinding compound.  By chance, it occurrred to me to try the following trick: a couple of twists with an RCBS case deburring tool.

Cold-blue if desired, clean the bore thoroughly, and head to the range to see how it shoots!

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