Tapering an octagonal barrel?

[Scota4570]

I have a 13/16 AF 32 cal I want to use for a Manton-esque  target pistol.  I'd like o bring the muzzle down to 3/4".  I have a mill.  I was thinking of using sheet metal spacers to raise the muzzle.  The barrel would be secured to the table with milling machine table clamps and V-blocks.  One clamp on a blank breech plug, one made of brass in the muzzle.  OR I could clamp the muzzle itself and shorten the barrel after.  The second way would allow one size sheet metal shim instead of two.  My mill is a regular vertical type.  My worry is that the barrel get loose and the cutter snatches it, ruining the job.  Setting up for a side cut seems sketch to me.   Other than my obvious need to purchase a horizontal mill, has anyone have any experience or advice on this job. 

[rich pierce]

File it. For 1/16” on a pistol length barrel seems like a 1 hour file job with zero risk. I make successive hacksaw cuts across the barrel where I want to file it. 2 strokes here, 4 further down, 6, 8, 10, 12 at the muzzle. File till saw cuts are gone then draw file. Looks authentic too.

[martin9]

+1 on filing it. Just look at it as good excercise

[45-110]

You do not need a horizontal mill if you have a vertical. There are several ways to fixture the barrel, one being a brass center in the muzzle for a table mounted center, clamp breech in swivel base vice, then pivot/offset the assembly for the amount of taper. Have everything clamped solid, side mill the flats with a 1/2" 4-5 flute carbide endmill, rotate as you go. Side milling leaves a nice finish. Mill towards the vise.
kw

[Daryl]

The mill should be easier than filing, just set-up time.
I've done the filing version - at a very much younger age.
That was enough.

[bob in the woods]

I did a barrel something like that , although it was a  .54  , using a scraper. It worked fine. I finished with a file.

[jerrywh]

I  have made about 5 or 6 tapered barrels for pistols using a vertical mill such as you described. I have an adjustable tailstock center that I use for the muzzle end and an indexing attachment for the headstock or muzzle end. The index head locks in any position. Both head and tailstock attachments have centers. I made an expanding mandrel for the barrel. The mandrel locks in the barrel and is long enough to put a lathe dog on the headstock end. I used a dial indicator to set the taper amount. by raising the tailstock end.  The cutter was a 1/2" 4 flute HSS milling cutter. Rotate 45° for each flat. Go slow and think. Fingering the depth of the cut is a matter of math. but the cut is not much on a pistol barrel.  These attachments were cheap at the time I bought them. I got them from some company that was bought out by.
 Here is what you need. https://www.amazon.com/Mophorn-Dividing-Precision-Universal-Tailstock/dp/B01NAQ0S6X/ref=sr_1_2?dchild=1&keywords=indexing+attachment&qid=1617993593&s=hi&sr=1-2
 It doesn't  pay to make one barrel but if you make three or more you can come out even on the attachments.

[JPK]

The last barrel I tapered I did on a mill by clamping to the table. A shim set the angle and when it came around to a cut flat a second shim was added to the first. This was a 32” barrel and there wasn’t any problems.

[Clint]

I have used my bridgeport vertical to taper and flare seven barrels at 42" long. Since the table won't go 42" , it takes 3 cuts (taper -waist -taper out). I like cutting on the side of the barrel as it doesn't chatter the barrel as much as a top cut. An old cast iron fence from a big jointer is used as my straight backing bar and I tape shims on the fence to maintain the orientation of the barrel. Mock it up on the miller and it will figure itself out, for the most part. Get a VIXEN file to fair the long tapers out. These files are used by auto body guys, they cut very fast and very smoothly.  Clint

[jerrywh]

Clint.
 Do you get any flex out of those long barrels??

[Clint]

Jerry,
The jointer fence is used to back up the barrel. Once the barrel is rotated four flats, a shim which is the same thickness as the cut is taped to the fence to stop any flex in the barrel. I make the waist cut first, then taper down to it from the breech. Flip the barrel and taper to the waist from the muzzle. A peice of two by three angle iron would make a good backing fence. This is just a milling jig, The magic is the vixen file.
Clint

[jerrywh]

Thanks Clint.

[Dphariss]

I use flood coolant. WS oil mix, when machining barrels.
I would not file it either. Getting too old for that.
Just do careful setup and a sharp cutter.

Dan

[Dphariss]

Like Clint said.