turning down a barrel

[cpileri]

Ran into a snag on my handi-mauser project... maybe this should be in the Gunsmithing area?

how do I turn about 0.5 inches of my muzzle from the .6-ish" O.D. it is to 0.5 inches?

I dont have a lathe nor any shop machinery.

I would rather do it myself if it can be done neatly.

I am willing to spend a considerable amount of time on it.

I have files, sandpaper, dremel, drill, cutting wheels, etc.

Any ideas?

It is necessary so I can thread the thing to accept the JP Recoil Eliminator.

thanks!
C-

 

[1911Tuner]

Threading a Barrel

Howdy cpileri,

It depends on a few things. mainly...how deep are the threads gonna have to be? That's dependent on the pitch, or threads per inch. The coarser the thread, the deeper it will have to cut into the barrel. If it
cuts deeper than the thickness of the steel, you can lop the end of the barrel off before you get a full thread.

A threaded section has a maximum diameter...the original diameter of the workpiece...and a minumum diameter...or the diameter at the bottom of the thread. If the minumum diameter calculates to be smaller than the bore diameter, the cutting tool will break through to air.

Calculate the depth of your thread by dividing one by the number of threads per inch to find the pitch, and then multiplying that answer by .6495. If the number is higher than the thickness of one wall of your bore, you can't cut that thread. For a barrel, if you cut the depth to
within .0625 inch of the thickness, you risk the end of the barrel snapping off.

Luck!

Tuner

 

[Black Snowman]

Assuming enough material will be left in the wall, ideally you'd want to remove the barrel and have it turned on a metal lathe. The kind of fixture you get from the lathe ensures that the resulting cut will be even and on-axis with the bore.

It might be posible to fake it by making some sort of jig in the bore that would allow you to turn a tool around the barrel evenly sort of like a lathe in reverse. Rotating the tool rather than the work. That way the barrel and reciever can remain attached and stationary but still get the nessisary precision. Don't have a clue as to a good way to pull it off though

Any ideas guys?

 

[Jim K]

The simplest method is to "take a walk" through the yellow pages looking for a local machine shop; most will do small jobs like that for a few dollars. (If your barrel is attached to the receiver, make sure how they feel about guns before waltzing in with one.) A gunsmith would be ideal, but most are heavily backlogged and no special knowledge is required to turn down a barrel as you describe. They could also cut the threads if you have the "recoil eliminator" or know what the thread size is.

If you are determined to DIY, put a ring of masking tape around the barrel, then start with a triangular file or hacksaw and cut evenly around the front edge of the tape, turning the barrel as you go. With the base of the cut defined, you can use the grinding drum on the Dremel tool to work the rest down. It will be slow, and take a good while (probably a couple of days), but it can be done.

Jim

 

[1911Tuner]

Screw Threads

The ONLY way to cut the threads would be on a lathe by form-turning
with a 60 degree tool and using the split nut. Using a fixture to hold a
threading die in the tailstock wouldn't be precise enough for this job.
I wouldn't trust it to be concentric with the bore axis, anyway.

If your accessory is foing to butt against a shoulder, be sure to remove
the last two threads in front of the shoulder so that the compensator
axis will stay concentric with the bore axis when you torque it down.

Makin' chips!

Tuner

 

[cpileri]

math

Thanks for the advice and math.
After doing the calculations, i come up with a wall thickness of .0885 inches!
Is that even thick enough to be safe?

Its a 1/2x28 thread, so 1/28 x.6495= thread depth
0.5" barrel thickness
0.5-thread depth= .177 total wall thickness, divided by 2 for one-sided wallthickness = .0885!

Even though more than .0625, seems like a wall less than 1/10th of an inch thick would snap easily. Am I wrong on that?
I would love to try that brake, but now am thinking a pin-on would be the way to go.
Help.
C-

 

[P95Carry]

88 thou is getting down there!! Mind you .. the helix comprising the major diameter does add something to the overall strength.

Tuner has covered most of this and well .. IMO lathe is all but essential .. it wants to be totally set up on center . this means too having a headstock spindle of sufficient I'D to take the rest of the barrel.

Threading too .. as Tuner said . that wants done with the leadscrew and halfnuts and 60º tool .... plus a ''run-out'' area at min dia for said tool ... with faced off shoulder to ensure all is on center when done up.

88 thou is 5 thou less than 3/32 ... and steel tube that thick is pretty stong... so you might ''get away with it'' .. but maybe as you say, a pinned on version may be way to go.

I guess if you could get someone to do the machining ... at worst - later, you'd only have to turn off a bit more at muzzle and recrown!

 

[cpileri]

aligned with bore

I ordered up a thread alignment tool (TAT) from dyna systems, also sold by Brownells, to keep it aligned with the bore. That seems easy enough. But i am still leery of turning down the walls of my bore to 'less than 3/32'!
I am no metallurgy expert, but seems mighty thin to me!
C-

 

[P95Carry]

seems mighty thin to me!

yep ... it is pretty thin!! And I still consider this a borderline deal.

However ... remember ... tubing is inherently strong by its nature ... and any pressure considerations are modest .. by the time the bullet exits muzzle, pressure levels have dropped way down - compared with breech pressures.

On balance I'll stick my neck out and say .. it'd work .. but another 10 or 20 thou on that wall thickness sure would help. If cost not prohibitive to get it done properly ... then as I said, worst case scenario ... you could trim off this portion and recrown .. all would not be lost. I am assuming you are not in to too much with the gun in first place.

 

[1911Tuner]

88 Thou

Yep..That would make it prone to break. It's not the pressure that's so much the concern...It's the barrel harmonics when it's fired. That, and the fact that a thread is going to have a sharply cut corner at the bottom,
sooner or later, it'll start a crack. If it was a .22 rimfire, it wouldn't be a
concern, but a centerfire rifle is gonna set up some lively vibrations in
that barrel.

The other option would be to thread the full diameter with a finer pitch,
ream out the threads on the compensator, and tread it to match. You'd
have to see what the size of the hole would be after removing the threads,
and whether toy'd then have enough material left to thread into it on a
finer pitch.

Sounds like the simplest way is a pinned-on comp, at any rate.

Luck!
Tuner

 

[Sunray]

"...How do I turn about 0.5 inches of my muzzle from the .6-ish" O.D. it is to 0.5 inches?..." You want to remove a half inch from the length? Or .050" (50 thousands) from the OD to thread it?
Either way, the best way to get it done properly is a machine shop. Won't be cheap though, but like Jim says, take a stroll through the phone book.

 

[1911Tuner]

Face or Turn

My read on it was that the wanted to reduce the diameter (turn) the end of
the barrel to a standard size and thread it for a compensator. Doable with
a threading die, but still not the best method. Lathe threading is the
best way to stay concentric with the bore axis.

Lopping off the end of the barrel is a parting/facing operation, and can be
done with a Dremel and a cut-off wheel, but it would still require that the
muzzle be trued, squared (faced), and recrowned. Lathe operations again
for best results.

As noted, threading does NOT raise metal to form the threads. They are
cut into the workpiece, (A form-turning operation) and to a required depth to get a full thread. The coarser the thread, the deeper the cut must be. If the required depth for his attachment is greater than the thickness of his barrel wall, the end of the barrel will fall off before he gets a full thread to
form.

Luck!

Tuner

 

[cpileri]

thansk

To clarify: I wanted to turn down the OD of the muzzle end from .647 to .5 or .51 so i can use the 1/2x28 threaded JP compensator.
But i think i am going to find a pin-on compensator (unfortunately not JP) that accepts a thicker OD and braze/weld it on.

I was really looking foward to trying that JP. Oh well. I'll save it for some other project.

thanks everyone!
C-