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Cutting a barrel
- Thread starter Chaz
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If you have a descent bench vice with hardened jaws you can mount it vertical or horizontally to the jaws and then cut a off the barrel using the jaws as a straight edge.
Leave it in as you file it smooth and square.
When perfectly flat and perpendicular to the bore it is time to chamfer the interior of the crown and round off the end of each flat with a diamond file or piece of sand paper glued to a block or wood.
The chamfer can be made with an electric hand or breast drill and a brass ball or a piloted stone with some emery paper or grit applied to the surface. It should be much larger than the bore so it will not go down in. All you want to do is break the sharp edge on the bore crown down through the land tops and into the groove bottoms and corners. If you don't get it all chamfered on the bore corner profile you will cut patches at loading.
The crown must be flat and true to the bore perpendicular, for best accuracy.
Usually you will have to set back the ram rod Ferrel and front sight which means to cut a new dovetail slot. If there is an under rib that too will need cut back and cleaned up often necessitating drilling and taping a new purchase screw up front.
Leave it in as you file it smooth and square.
When perfectly flat and perpendicular to the bore it is time to chamfer the interior of the crown and round off the end of each flat with a diamond file or piece of sand paper glued to a block or wood.
The chamfer can be made with an electric hand or breast drill and a brass ball or a piloted stone with some emery paper or grit applied to the surface. It should be much larger than the bore so it will not go down in. All you want to do is break the sharp edge on the bore crown down through the land tops and into the groove bottoms and corners. If you don't get it all chamfered on the bore corner profile you will cut patches at loading.
The crown must be flat and true to the bore perpendicular, for best accuracy.
Usually you will have to set back the ram rod Ferrel and front sight which means to cut a new dovetail slot. If there is an under rib that too will need cut back and cleaned up often necessitating drilling and taping a new purchase screw up front.
You'll need a small metal square, a hack saw, tape measure, a metal scribe or sharp nail and several new flat files. Mill or Bastard files will do nicely.
Having a good steady bench to hold the barrel is handy too.
Use the tape measure and scribe to mark the length at one location.
Use the square to transfer the length marking around all 8 surfaces of the octagon barrel.
Use the hack saw to cut off the extra material leaving 1/32 to 1/16 of extra material.
Use the flat files to square up and smooth the cut off surface, resting the square against the 8 sides of the barrel.
Visually note the high areas and file them down a bit.
Constantly recheck the square condition of the cut using the square, measuring in at least 4 directions.
When the end of the barrel is square and smooth, get a spherical grinding bit that is 3/4" to 1 inch in diameter. (They often have a 1/4" shank for an electric drill but NEVER use a power drill at this stage).
Place the grinding bit into the bore and using your finger pressure only, rotate it back and forth.
It will remove the sharp edges where the bore meets the newly filed face of the muzzle.
Do this until the size of the corner break is at least as deep as the rifling grooves. Deeper is better (up to a point).
Once the sharp edge is removed, use some 160 to 220 grit black, silicone carbide sandpaper to round off the newly made corner break.
You can leave the muzzle in the white or blue or brown it as you see fit.
Having a good steady bench to hold the barrel is handy too.
Use the tape measure and scribe to mark the length at one location.
Use the square to transfer the length marking around all 8 surfaces of the octagon barrel.
Use the hack saw to cut off the extra material leaving 1/32 to 1/16 of extra material.
Use the flat files to square up and smooth the cut off surface, resting the square against the 8 sides of the barrel.
Visually note the high areas and file them down a bit.
Constantly recheck the square condition of the cut using the square, measuring in at least 4 directions.
When the end of the barrel is square and smooth, get a spherical grinding bit that is 3/4" to 1 inch in diameter. (They often have a 1/4" shank for an electric drill but NEVER use a power drill at this stage).
Place the grinding bit into the bore and using your finger pressure only, rotate it back and forth.
It will remove the sharp edges where the bore meets the newly filed face of the muzzle.
Do this until the size of the corner break is at least as deep as the rifling grooves. Deeper is better (up to a point).
Once the sharp edge is removed, use some 160 to 220 grit black, silicone carbide sandpaper to round off the newly made corner break.
You can leave the muzzle in the white or blue or brown it as you see fit.
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Save the cutoff.
I just scribe a line a one bbl flat, clamp the bbl horizontally in a stable vise and hacksaw it off staying away from the line a mite.
If it's a straight bbl, I then square the muzzle w/ my disk sander using the right angle attachment and polish. The muzzle end is chamfered as well as the bore.
If it's a swamped bbl, 2 shims are taped on, one on a bottom flat and the other on a side flat. This is done to align the bore perpendicular w/ the disk face when held against the right angle attachment and table. The polishing and chamfers are then done.
Yes...I've done this job w/ only a file, but the disk sander is way faster, so I use it.....Fred
If it's a straight bbl, I then square the muzzle w/ my disk sander using the right angle attachment and polish. The muzzle end is chamfered as well as the bore.
If it's a swamped bbl, 2 shims are taped on, one on a bottom flat and the other on a side flat. This is done to align the bore perpendicular w/ the disk face when held against the right angle attachment and table. The polishing and chamfers are then done.
Yes...I've done this job w/ only a file, but the disk sander is way faster, so I use it.....Fred
Chevythunderman
40 Cal.
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What I did the first time I cut a barrel off was to keep the cut off end and turn it over and use it to check my squareness of the cut. If you place it on top of the barrel with the factory cut edge you can use a straight edge and check each flat against the barrel and cut off piece. I used a square to check it when done and it was perfect. I had my machinist check it when I was done just to see how well I did and he said that was the closest to square he had ever seen cut with a hacksaw at home. Or maybe I just got lucky.....
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A properly used file and spotting fluid is every bit as accurate as using a mill or lathe,just takes longer.
The barrel cut off is a good idea but a flat plate about 3 inches is diameter with a brass tight slip fit bore spud and some spotting fluid will get you much closer to square, especially when dealing with a tapered barrel.
If I was going to do the job by hand I would make a piloted crown cutter which will insure nearly absolute square with the bore which is what you really want not necessarily square with the barrel exterior which is usually not precisely the same. This is so because all bores have tapered or spiral run out to one degree or an other and some even have a bend in the bore and the outside is perfectly straight.
These things occur in the deep hole boring phase for various reasons.
A slightly canted crown can still be accurate as long as it is cut cleanly.
The barrel cut off is a good idea but a flat plate about 3 inches is diameter with a brass tight slip fit bore spud and some spotting fluid will get you much closer to square, especially when dealing with a tapered barrel.
If I was going to do the job by hand I would make a piloted crown cutter which will insure nearly absolute square with the bore which is what you really want not necessarily square with the barrel exterior which is usually not precisely the same. This is so because all bores have tapered or spiral run out to one degree or an other and some even have a bend in the bore and the outside is perfectly straight.
These things occur in the deep hole boring phase for various reasons.
A slightly canted crown can still be accurate as long as it is cut cleanly.
