Swamped Barrel

[Old Ford2]

Would it be practical to swamp a barrel on a milling machine?
I would like to leave the bottom flat not swamped.
Any suggestions?

Old Ford

[Stophel]

Probably not.  And I don't know that you even could leave the bottom "unswamped".  Would be very difficult.  Almost like a raised rib.

[billd]

It would be fairly easy on a large CNC machine but without somekind of tracing attachment on a manual machine I wouldn't try it . My CNC miller doesn't have enough travel.
Bill

[Jim Kibler]

With care and patience it can be done on a manual mill.  I just did one a week or two ago.  Takes some planning and quite a bit of careful setup.  From a cost effective standpoint it makes no sense.  Took me a little more than two days to complete.  I just didn't want to wait for a custom barrel.  It did, however, turn out as well as any comercial barrel I've seen.  I must ask why you would want to leave the bottom flat straight?  I can provide some more information about the process if you're still interested.

[brokenflint]

Does milling swamp and leaving a single straight flat produce stress / change of aim point like in high power barrels?

Broke

[Bill of the 45th]

Much cheaper to sell the straight barrel and buy the profile you want.  If you try it and goof it up you have an expensive piece of scrap.  Unless of course you just want to try it to see if you can do it, the go for it.

Bill

[Pete Allan]

I have done quite a number of them on a Bridgport mill  BUT  I made a VERY strong fixture to hold them while I am cutting. The fixture is about 3 feet long and has clamp bolts every 6 inchs. Almost forgot to mention -- I use a right angle head with a stagger tooth slab mill cutter. I have done them with a regular end mill but never again. One little slip with an end mill and it's a junk barrel or a bunch of pistol barrels

[Old Ford2]

Thank you all for your thoughtfull input....guess I'll leave that .32 cal. straight barrel alone.
Old Ford

[Dphariss]

I have tapered barrels  or increased taper. I suppose that I could do a swamp. But its easier to buy one.
I tapered a barrel the other day and did "one little screwup" and now I need to set it  back up and make a little different taper. Fortunately I have enough length to get it right the next time bay moving the taper back 2-3 inches. Its got .200 taper over 28" so moving  back a little gives enough metal to start over.

Dan

[Karl Kunkel]

If you did leave one flat straight, wouldn't the barrel want to banana on you?  You'd be relieving some internal stress with the removed material on seven of eight sides.  If the barrel stayed straight, would the harmonics and thermal expansion/contraction  be affected?

Disclaimer: I'm neither a machinist or metalurgist, just trying to understand the impact this would or wouldn't have.

[Chuck Burrows]

If you did leave one flat straight, wouldn't the barrel want to banana on you?

Maybe not - some English smiths made tapered barrels on some dueling pistols that were tapered on the bottom flats leaving the top flats straight for aiming purposes...

[oldiemkr]

Pete and Jim,

Would you care to share the setup you used to swamp a barrel on a mill?

I've been thinking about slightly swamping a barrel on a gun that needs restocked.

IMHO the swamp on new barrels seems a bit more than some originals I've seen.

            Denny

[Jim Kibler]

Pete and Jim,

Would you care to share the setup you used to swamp a barrel on a mill?

I've been thinking about slightly swamping a barrel on a gun that needs restocked.

IMHO the swamp on new barrels seems a bit more than some originals I've seen.

            Denny

Denny,

Here's a quick synopsis of the process:  The desired profile is determined.  This is basically a series of straight segments.  I ended up having seven or eight straight segments to get the profile I wanted and not have any transistions too abrupt.  Determine how much needs to be removed from each flat at each segment transition point.  Indicate each flat of each segment in and cut.  After the entire barrel is milled, it will probably need a little hand work to smooth things out and to blend the segments a little better.  I used a vixen file that was thin enough to bend lengthwise along the barrel initially.  This did a good job of smoothing the transitions out.  After this I drawfiled as usual.  If you have any questions just ask.

-Jim

[Acer Saccharum]

Banana depends on the individual barrel, and how much stress is in the steel, or is created by your milling cutter.

I have milled barrels on one side, and when looking through the hole, I could no longer see thru it, there was so much bend. But when I milled the opposite side, it was perfectly straight again.

I'm not saying this will happen with YOUR barrel, but it's nice insurance to be able to throw it out and drill and ream a new blank on the spot. If you don't have that luxury, then be aware of the risks involved!

Some barrels are almost stress free, or have been normalized to get rid of the stress. You would probably have better luck with one of those.

But how do you know what kind of barrel you have? You don't, until you cut into it.

[omark]

guess if i was going to do something like that, i would not swamp the 3 bottom flats.   just my idea, but would still be crooked when done.    mark   

[J Shingler]

"Maybe not - some English smiths made tapered barrels on some dueling pistols that were tapered on the bottom flats leaving the top flats straight for aiming purposes..."

Yes I agree as I have seen swamped five sided barrels with the bottom still being round but that was on a short pistol barrel not a long rifle barrel that I would want much better accuracy from. I think one would want it symmetrical on all sides.
J shingler

[Acer Saccharum]

A wrought iron barrel does not have the internal stress that a bar of modern rolled steel has. What you could get away with the iron, I doubt the steel would do.

[Dphariss]

A wrought iron barrel does not have the internal stress that a bar of modern rolled steel has. What you could get away with the iron, I doubt the steel would do.

A modern steel bar with stresses is not supposed to be made into a barrel in the first place. They need to be normalized before the process starts.
But ML barrel makers don't always realize this it seems.


Dan

[Acer Saccharum]

Milling induces stress. Even a normalized bar will develop stress after milling. A dull milling cutter makes for more stress than a sharp one.

Probably why they stress relieve, eh, after rifling.

Climb milling, where the mill is trying to pull the metal into the cutter, induces the least amount of stress, but baby, you'd better have a sturdy machine with very little backlash in the screws nor slop in the table. If your machine is in poor condition or out of adjustment, you'll either yank the barrel out of the fixture or break the cutter.

[Dphariss]

Milling induces stress. Even a normalized bar will develop stress after milling. A dull milling cutter makes for more stress than a sharp one.

Probably why they stress relieve, eh, after rifling.

Climb milling, where the mill is trying to pull the metal into the cutter, induces the least amount of stress, but baby, you'd better have a sturdy machine with very little backlash in the screws nor slop in the table. If your machine is in poor condition or out of adjustment, you'll either yank the barrel out of the fixture or break the cutter.

You need to ask if they really do stress relieve after the machine work, not likely in the world of MLing.
GM 1137 swamps seem to show this by having a blue tint that looks heat related. The GM cartridge barrels that are only tapered don't show this but they are 4140/4150. The rest of the ML barrel makers? Don't hold your breath. But if cut rifled and the material is right BEFORE its machined and the maker knows how its not necessary at least with properly treated 4150. But the cutter used, feed speed and coolant are all important. It does not take long for 4140-4150 to dull a cutter and start heating the work even with flood coolant. But I am not a trained machinist and my feed is hand powered.
Some makers at least use cryoed steel since it machines easier and the cuts are smoother in the 41xx barrels.
But they still often do things a little differently. Krieger for example claims they drill the rather complex garand barrels then contours then reams and cuts the grooves with the gas port in the groove. But they lap and they get 350-500+ for a barrel and these are not octagonal.

There are other things as well but I better  before I get in trouble.

Dan