machining a gun barrel

I am sure you know the answer, but whilst boring a small hole on my lathe I was wondering how the 16" gun barrels, of secound world war battle ships, were bored out, and how the rifling was put in. Not that I'm thinking of making one

Try this for barrel boring.

http://www.practicalmachinist.com/vb/antique-machinery-history/naval-gun-factory-d-c-1943-pic-192009/

You cut it by putting a cutter on a male rod rod or guide and the rod goes down the bore. The cutter then flies up and down the rod turning as it does so. You can use multipoint cutters, or single point cutters and index the guide round, or a combination, whichever led ot less distortion in that process. IIRC they indexed to cut opposite grooves.

Thats fine for a constant twist, but if you need an accelerating twist as in short barreled high velocity aircraft guns, then you attach a cam to the guide, which increases the rate of twist towards the muzzle where acceleration is less. Reduces inertial loads on long high payload projectiles (a cannonshell), which because of their length need a high spin rate to stabilise the projectile, and you want to keep the barrel short for weight purposes

You can broach them - the Americans do this in final sizing which also stretches the innermost layer beyond its elastic limit, Creates a compressive stress which needs to be overcome before the barrel expands, so allowing for a stronger barrel for less wall thickness. We achieve the same effect after cutting using hydraulic pressure, and we call it auto frettage.

Whitworth achieved it latterly by wire winding, so with naval ordnance you are actually looking at a cotton reel or bobbin - a jacket laid over the wire. Another advantage was to act as an insulator - naval guns on big ships fired in broadside - in a crosswind effectively. So stiffness without being stupidly heavy is an advantage, and that construction reduced thermal distortion- and maintained the pointing line in hot barrels.

Nowadays with smaller guns they hammer form a billet over a mandrel usually with a rotary hammer. Roughing out a blank ready for fixtures like sights and breech only takes a few moments - literally.

Edited By mgj on 29/06/2012 19:00:13

There is another method of making barrels for smaller calibres, it involves the making of a Carbide form with the rifling formed on it.

This opens the way to make barrels with Ogive rifling and all without cutting metal.

The method is swaging, the rifling form is attached to a rod and is hydraulically pulled through a prepared barrel blank all in one go!

This gives the inside of the barrel a Rockwell hardness of 95 + and is exceptionally bright and smooth.

Space age lubricants are used as it is done. Obviously the bore of the blank barrel and the form have to be carefully developed to give the right size bores.

This is a development of an American Company called Oakley who make bespoke barrels for re-barreling firearms.

Clive

You've spoilt it! If I'd got in first I would have spun a tale of how small children holding large, well sharpened gravers would be spuin down the bores - the lucky skillful ones getting this job and avoiding being sent up the chimneys.

Neil

Sorry.!

Clive you are right about modern manufacturing. A lot of modern barrels are stellite (or more modern equivalent) lined against abrasion and heat. They are using a very thin bore in carbon fibre I think too.

Still I think a lot of match barrels are still cut in the old way, and then polished. In the early days with hexagonal rifling - did they cut that, or form the hex and then hot twist, before final finishing of the outer profile? Modern SAA barrels twist at about 1:8-1:10. How they did it with those long slim bullets and low velocities which must have needed twist rates in the 1:5 mark at a guess, or did they just accept a tumble point at 7-800 yards. What was a Martini Henry sighted to?

Not entirely on the point, but I've been a .22 target shooter for more years and cartridges than I care to remember. I recall going to the BSA factory when they still produced Martini actioned small-bore target rifles. An old chap equipped with a mallet and two pads straightened up the barrels after machining , sighting through the bore to a skylight and knocking them into shape

I still have a 1960s BSA Mk 3 which shoots straighter than I can.

Andy

The other interesting big gun technology is the breech

Ericsson developed the hoop system which greatly increased its strength

Capt. Stockton made a copycat gun with a breech of solid metal and nearly wiped out the entire presidential cavalcade in 1844

**LINK**

A couple of photies from ra net

The Yanks spent 5 unsuccessful years trying to circumvent the welin breech block patent which had a very high thread engagement rate(75%), short length and very fast reload

uknaval gun factory

**LINK**

Edited By Ady1 on 30/06/2012 00:46:23

Whitworth achieved it latterly by wire winding, so with naval ordnance you are actually looking at a cotton reel or bobbin- a jacket laid over the wire. Another advantage was to act as an insulator

----

The British Army used to wind wire around the barrel of a lee enfield 303 if it was going to be used as a grenade launcher

Lobbing a grenade sized lump of metal could burst the rifle barrel if it wasn't reinforced

That naval gun factory piccy is interesting

The further away barrels are being machined from the breech block end

The two closer ones are being machined through the muzzle

Anyone know why?

Spot on Andy superbly accurate.

The BSA were drilled out and a dolly hydraulically pulled down to slap the rifling in. The swaging was for the choke except BSA called it swaging, to you and me its a hammer blow before being cut off so can see choke on the breach and muzzle of certain BSA older barrels. Martini are unchoked.

Similar method Webley used a couple of years before going under was to buy tubes in from Lothar Walther and draw a dolly down often called button rifling.

Hammerli had a pre world war 2 hammer forging machine at the Daimler Puch factory prior to being bought out by Anchutz. CZ supposed to have one as well.

Many rifle barrels and some shotgun barrels are made today by hammer forging, this is a procees where a male pattern is used and the barrel blank is drilled, the former inserted and then fed into a hammer forging machine thus swaged by the hammers over the former and a finished barrel produced which in the case of a rifle has the rifleing and chamber completed. The machines are of massive proportions and the barrels produced are excellent quality. The process is also quite fast and thus efficient for production.

Not used for naval or artillery barrels or course.

The older methods were and are still used, i.e. deep hole drilling, draw reaming, honeing and either button or cut rifleing.

Nothing beats the human eye for straightening barrels and the method is still used today--no machine has been developed to facilitate the "viewing" of barrels.

At one time in service I was an inspector and had to carry out inspections of stored kit/components and would have to look at 1 in the first 10 and then 5 in a 100.

Went to one store and it was a barrel store, racks of gun barrels from 20mm to 12". all racked and had pointers on the ends so that they could be turned every month to stop, 'Sagging' in the middle.

Only thing was that no one had turned them and you could see the, 'Sag' when looking along the racks.The 12" barrel was just laying on the concrete floor and had never been moved in umpteen years.

Also was with Artillery regt. for some years and saw the big guns close up and how accurate they are. I have seen three Batteries of six guns at different positions and distances land all 18 projectiles in one 50mtr. place at the same time. Also one gun fire two shells, one at high angle and one as 'Direct' fire and both shells hit the target at the same time.

My Father was the Gun Sgt of the 7.2" gun on Europa point in Gibralter before the war. I have photos of how they dragged the barrels up the rock and winched it step by step to the gun point.

Tie bolts and rings grouted into the rock face were used as winch and anchor points.

Clive

Clive, it has all changed from Pas day. Now the gun is gps located. The FOO is gps located, the traget is laser ranged for a fire mission. You know from GPS survey, altitude of both gun and target, and your barometrics are well enough known. So very often they don't range but will set TE and QE off.(Set your spirit levels for those who haven't done it - you offset the levels and then level the bubble to set range and line to target, or you can do it automaticaly off  laser ring gyros) A battery of self propelled 175s will now burst fire a fire mission, loading on the autoloaders/flick rammer. The individual gun dispersion is fed in for each gun, and the whole lot arrives without warning with a calculated spread built in.

Actually its quite wrong to suppose that a barrel needs to be straight for accuracy. All that matters is that it does not move. It needs to be moderately straight in general terms so that the proj goes down cleanly, but beyond that the line of departure is fixed by the line of the muzzle, and so long as that is fixed with respect to the sights all will be well.

The problem really comes when you have something flexible like a ships hull between director/acquisition radar and turret (now we fit strain gauges to measure twist and deflection in the hull and compensate) or in a tank barrel which will cool assymetrically and is very long for its dia. Hence the calibrated mirror and laser projectors to measure where the barrel is pointing with respect to the sight line.

Why would you machine from breech or muzzle. The barrel blank will very often just be a tube. You still have to machine the chamber, and the taper end of the rifling. You also have to finish to length and profile. Length is particularly important for accuracy because length controls shot exit timing, and hence where on the vibration pattern the shot exits. You need for consistency to time it so the barrel is moving slowest on the theoreical sine wave. Profile affects the undamped natural frequency of vibration, so thats important too.

Edited By mgj on 30/06/2012 12:34:46

I have to say that I left the army in 1977 so things have moved on I am sure!

I did have to carry out a barrel droop measurement on the 18 155mm Howitzers we had and all of them registered about 8 to 10 secs droop except one which had 21 secs upwards.

We were told to ingnore that in calculations though it seemed to shoot to point of aim happily anyway.

Clive

Droop. I'm not sure about the artillery. In those days one ranged anyway, so that sort of error would be taken into acount, though I'd have thought you'd have needed to offest, since most missions would have been one gun adjusting. You may have found that jump in the slides counteracted the droop! Still they would have known their business, and there must have been limits beyond which one would have to compensate, and inside which you didn't. That was the American 155 presumably.

Tanks of course are the "snipers" of the ordnance world, and are looking for a first round hit on a target no bigger than a metre square at a mile and half or so. Once you had boresighted and shot the gun in at 1100 metres, you set the muzzle reference sight, and the computer could measure the difference between the zero and the current position of the muzzle with respect to the sight and correct accordingly.

Actually you can bend like a banana or tie in a knot and still have same accuracy.

I couldnt envisage machining from muzzle end unless it was faced off and or having something pulled through.

The tubes are directional and should be marked accordingly in direction they were drawn. Why, its the grain structure and have known producers crap 100's of blanks and not have a clue why. Finished rifle blanks will always have a detent/punch mark at one end.

Hammer forging has been around for centuries in the form of Damascus.

Quite so, because even in perfectly still air, and on a non spinning earth, the bullet/projectile will still curve in flight(if spun) because the laws of physics say it must, because of cross flow velocity, precession/nutation and the magnus effect. So any single zero point can only refer precisely to a single point in the trajectory. To remove such erros you really need a calibrated graticule, which tank sights have, and you can see the curvature compensation increasing with range The curvature in flight is not very pronounced with small arms.

I don't think there's any doubt that one would normally machine from the breech, mainly because you want any roughness in the cuts to go with the proj, as well as the grain structure. Ordnance barrels are commonly forged rather than drawn of course. But you still need to face off the muzzle etc. So it is to be expected that it might be put into a machine muzzle first, at some stage in the proceedings -even small arms which may be threaded for silencers and flash eliminators.

Jon, Just to clarify hammer forging of Damascus tubes bears no relationship to todays hammer forging of barrels, the process was devised in Germany after WW1 to get around the surender treaty that prevented Germany from having any rifling machines which was supposed to prevent them manufacturing arms.

Damascus barrel forging is done by winding a flat strip of material around a former and welding it together in a forge to make a rough barrel blank. This would then be spill bored or reamed, chambered, honed and profiled on the outside to make a finished barrel.

Hammer forging today [for say a shotgun tube] starts with a blank which is approximatly 15" long with drilled hole about 3/4" dia, this is then inserted into the hammer forging machine with a male former of exactly the internal barrel and chamber dimensions, the machine has a series of opposing hydraulic hammers and when the finished tube emerge's it is 30" long with a bore of 0.728"//18.5mm for [12g] Process time approx 3/4 mins. The exterior has spiral pattern which is then ground off and polished. Some rifle makers don't remove the spiral pattern and it does look quite decorative.