Shotgun barrel porting home machinist.

[icebones]

Have an old 20 dollar single shot (with broken trigger) I want to expiriment on. How exactly would someone port a shotgun barrel and then deburr the holes from the inside of the barrel? I was planning on making about 5 ports on each side angled at 25 degrees from the sight bead. Planning on using a regular manual mill and drill bits/reamers for this. Any one know how firearm mfg's port a shotgun barrel? I have used wigglers and other tools to deburr drilled holes on flat pieces of stock, do they make any tools for deburring holes in the inside of pipes or anything simmilar or would running a reamer through the hole take care of the burrs?

 

[icebones]

PS, worked 3 years in a machine shop, but only worked on engines, so please dont be afraid of using "machinist jargon" i know my way around a shop. thanks

 

[Jim Watson]

I had a couple done locally as follows.

Clamp the barrel in the mill vise and center it under the chuck or collet.
Roll it to one side until the rib or bead contacts the vise jaw. I don't know how many degrees that is but it is close to what the gunsmith jobs come out at.
Make holes with a ball-end mill, it will leave less burr than a drill.
Index down the row, then roll the barrel the other way and do the other side, measuring to get the same starting point. Start point should be behind the choke constriction of a fixed choke barrel, and darned sure behind any screw choke threads.

I have 16 holes per side 1/8" diameter, 1/8" apart, starting 2 1/2" from the muzzle. That gives port area about equal to the bore cross sectional area. Since it is on a Remington 1100 trap gun the combination of ports and gas operation make for a soft shooting gun. One O/U shooter said "You could shoot that gun of Jim Watson's off your nose!"


A split rod with flap of fine emery was enough to clean up inside. Don't polish so hard as to affect the choke constriction.

 

[amlevin]

30 years ago I saw a lot of these self ported barrels. We all laughed at the guys that hadn't deburred the inside of the "ports". Funny though, after a round of trap they seem to have disappeared.

If you do have any burrs after drilling or milling, a round stone can reach most. Also, take a 3/8" wood dowel, cut a slit in the end with a razor saw, thread a piece of crocus (NOT emery) cloth through it, and run the "flap" into the barrel using a drill to turn it. The Crocus will polish and knock off most of the burrs.

To finish the outside, a little careful work with a countersink can make the holes look real nice. Mounting the countersink in a hand vise can let you chamfer the holes evenly around their circumference. If you do it with a press the chamfers will be deeper on the highest part of the radius. Hit the white metal with some blueing and your done.

Suggest you start with a minimal amount of holes and then pattern the gun. You can add more but it's real difficult to plug the extra holes later.

 

[rcmodel]

I might consider greasing the bore and then pouring a melted lead plug in the section you want to drill.

The solid lead will back up the drill bit and prevent burs from forming when it breaks through the barrel wall.

After you finish, knock the lead plug out with a rod.

If you don't want to mess with that, just polish the burs out with a slotted 1/2" dowel rod and 320 emery cloth spinning in a drill when you get done drilling.

rc

 

[icebones]

I had though of the dowel rod/emery cloth idea but I didnt think it would work. Good to see some fellow shooters know their way around a mill thanks my friends

just noticed my horrible grammar too. I was pretty tired last night.

 

[Howard Roark]

A dowel and emory cloth will work fine. The best method would be to use a flexible hone brush.

The "correct" way to drill ports would be to put the barrel in a vertical rotary table vise or indexing jig and index on top dead center (TDC). Rotate 45deg. and bore the ports. Rotate back 90deg and bore the opposite side holes.

There are many ways to skin this cat and they all work.

 

[Clipper]

I use a carbide deburring pencil. the ball will fit through a small hole and if you're careful, it'll deburr and chamfer both sides at once...