Project Number 3,712

[Evil Dog]

Just what I need... another project... this one is number 3,712.... I think I am currently working on number 27.

On to the planning stage !!!  I've this half scale Napoleon with a 2 1/4" bore that is just begging to be worked on.  Up until recently I have never actually hit anything that I'd deliberately aimed at in excess of 50 yards.... totally underwhelming.  So started experimenting with attaching a wood sabot to the zinc ball.... much better, now I can keep on a 4' square piece of cardboard at more or less 100 yards... not thrilling but a definite improvement.  I've always kept the powder charges on the conservative end of things, so far haven't exceeded 500gr Cannon with a 1.5 pound zinc ball.  Considering the breech end is 5 1/2" diameter and tapers to 3 1/2" just before the muzzle swell that doesn't leave all that much in the way of wall thickness with a 2 1/4" hole going through it.... not even close to approaching the "one caliber of thickness" rule of thumb.

Definitely time to do something.  I'd briefly considered selling the barrel and replacing it but haven't found anything I might like for less than $650 plus shipping.  Then I had this flash of rationality (as mentioned in a different thread).... why not sleeve this barrel to a smaller caliber !!!!  Bound to cost a heck of a lot less than replacing it... or at least I would think so.

So here's the idea.... and please let me know where I am going astray.

The current barrel has a liner that measures 2.350" at the muzzle.  I know that there is a slight constriction about 6" down the bore as I can feel it when test fitting wood sabots.  Can't actually see anything, but a sabot will get tighter in the bore at around 6" and then loosen up again at around 8" from the muzzle.  Shouldn't be all that much trouble to use a cylinder hone to open up that constriction.  Then most any competent machine shop should be able to turn a shaft 2.34" by 30.75" and bore it 1" ID for say 29.75" (leaving a 1" breechplug).  Might also have just the first inch or so at the muzzle  and the last 3 inches at the breech being 2.34" with the remainder being 2.33".... not sure why that would be a good idea but it sounds like it might be.  Since the existing barrel is already vented, building up air pressure resistance when inserting that sleeve shouldn't be a concern.  Hopefully it would be just a matter of slathering it up with epoxy and sliding it in.  Then plug up the old vent and drill a new one.

Sounds too simple.... where am I going wrong?

[Santa Dave]

You are correct! it sounds TOO simple!
isn't there a natural law that says if it's easy it won't work?

Oh Yeah "The best planned lays of mice & men-------blah blah"

I hope it works!

Santa Dave

[Cat Whisperer]

Sounds like your work-load is lightening up with ONLY 3,712 projects left to do!

Putting a 2.34 cylinder into a 2.35" hole gives you only 0.010 clearance on the diameter.  It "should" slide in if everything is straight and round (cylindrical).  But that's tight clearance, so make sure you check it's fit before applying glue.

I have a something-scale napoleon with a 1-7/8" bore that I'm considering boring and lining to an inch or so bore.

[Don Krag]

Only 3,712!? Slacker...get busy!

Things I thought were perfectly round...never seem to be when it comes to tight sqeezes!

[dominick]

 

Hopefully it would be just a matter of slathering it up with epoxy and sliding it in.

Most of my barrels [about 90 percent of them] are "built up barrels" ie,  barrels assembled from multi layered tubing and this is the method  I have found that works for me.   If your barrel is steel, or you have a steel liner in it, then epoxy is not necessary. You can chamfer the new  insert at the muzzle end and weld it to the muzzle end of the barrel or to the existing liner tube.  Then sand the weld  smooth with a disc sander.  I've assembled barrels with less than 10 thousands clearance [1 to 5 thousand].  They have to be assembled with a press. Use  plenty of WD-40 and make sure there are no rough spots that will cause metal pickup and then press the pieces together. If you want to play it safe then 10 thousand's should be the maximun amount of clearance.  The more clearance between the tubes, the more you rely on the inner liner to absorb the energy of the blast. Also,  Maybe you should see if the machine shop can bore the barrel a few thousands to insure a more uniform clearance.  Just some suggestions  for you.

[Double D]

First is there a reason you don't want to fix the existing bore? Honeing isn't  for remove metal its for for  smoothing metal. Yo  ned to have the bore reamed to make it uniform, then hone it to smooth it.

For a new liner, I'm with Dom on this one. After you get the new liner in place just drill through you existing vent and add a vent liner

Make your bore  1.75.

For the  other 3,711 project please see the sticky at the top of the board listing all our sponsors, the need the work...

[Evil Dog]

After you get the new liner in place just drill through you existing vent and add a vent liner.

Make your bore  1.75.

As mentioned earlier. this barrel has a 2 1/4" hole with 1 1/8" thick walls at the breech end tapering down to .625" just before the muzzle swell.  Don't know about you, but to me that sounds pretty darned thin.  I would feel much safer with a smaller hole in the same barrel.

The existing vent enters the bore approximately 1/4" in front of the breech face.  To install a new liner and then drill through the existing vent would require the new liner be basically a piece of pipe with no integral breechplug.  Instead it would butt up against the existing breech face.  Is this correct?

I had originally considered going 1.75" and may still do so as I have plenty of golf balls left over from a previous mortar.  The thought behind going to a 1" bore is that my existing barrel tapers down to 3 1/2".  To maintain a "one caliber" minimum wall thickness a 1.75" bore would require a 5.25" diameter barrel... I have that in the breech end, but by the time I get down to the muzzle there would be a .875" thick wall... significantly less than "one caliber".  By going to a 1" bore though at no time would I have less than a 1.25" thick wall.  Somehow the thicker wall just sounds safer.  For the new liner itself, what sort of steel should I be looking for?

Make sense or am I just being obsessive?

[Double D]

Yes I forgot to figure in the breech plug...plug and drill new vent.

You don't need one calibar wall full length, only in the breech.  As the ball moves down the bore the pressure drops. You will have a steel liner inside a steel liner and it will be plenty thick at the muzzle.

[Evil Dog]

Ok, yes to the breechplug.  How thick does the breechplug need to be presuming a 1.00" to 1.75" bore?  It would be butting up against the existing breech which is approximately 3" thick.  What sort of steel am I looking for to have the liner made from?  Looking through the "resource list" the closest I've found is DOM with an OD of 2.50" and a .500" wall thickness.  Should be easy enough to have it turned down to 2.35" or even 2.30" and a breechplug welded in.  I will presume that it is "mild steel".  Just for giggles I looked at the surplus rifled barrels over at Big Sky thinking it could always be turned down.... you don't want to know the prices.

[GGaskill]

If you use DOM tubing, you will have a welded seam in the bore.  Try to find seamless.  You can probably find 4130 seamless of the right size if you can find the right source.  That would be good stuff.

[dominick]

How thick does the breechplug need to be presuming a 1.00" to 1.75" bore?

I would make it 1/2" thick minimun and "press fit" it into the I.D. of the liner tube and then weld the back side to the tube [chamfer a "V" into the backside of the plug prior to welding] and then sand the weld flush.  Make sure the back of the new liner is square so the plug is resting against the breech.  If you cap the end of the liner with a plate instead of a plug, moisture from swabbing the barrel will collect in the seam and eventually corrode through the weld.  You want a press fit on the plug to prevent corrosion from setting in between the liner and plug.

To install a new liner and then drill through the existing vent would require the new liner be basically a piece of pipe with no integral breechplug.  Instead it would butt up against the existing breech face.  Is this correct?

You always want to use a plug in any liner type setup.  Sliding an open end tube into an existing barrel will create a spark trap and create an area for corrosion.  There is no way of telling if the tube is seated 100 percent around the existing plug. 

[Evil Dog]

Dominick mentioned the multi-layer technique of barrel lining in an earlier post.  This has got me to thinking.... did a bit of preliminary looking around for tubing, 4130 or otherwise.  To go from a 2 1/4" bore down to say 1 1/2" would require tubing with a with a 3/8" wall thickness.  The closest I've found so far is DOM with an OD of 2 1/2" and a 1/2" wall thickness.  Being DOM though there will be a seam somewhere and it is described as "mild steel".  Should be easy enough to have that tubing turned down to 2.35" or so OD.  That would then have me down to a 1 1/2" bore.  Then.... take a piece of 4130 seamless with an OD of 1 1/2" and having the thickest walls I can find (looks to be 1/4" max) and weld in an appropriate breech plug.  This seamless liner would then be inserted into the DOM liner which was inserted into the existing bore... drill and install a new vent liner and hopefully that should work.

Anybody see any flaws in this approach?

[GGaskill]

I would not expect the holes to be as accurate (either in absolute dimension or roundness) as drilled holes, especially not as reamed holes.  The smaller tube might or might not fit the larger one well.

[Evil Dog]

Hey George.... looking at Metal Express from the resource list, they show a 4130 cold rolled 2 1/2" diameter as being available in Chino.  a 38" piece running under $140.00.  Is cold rolled.  They list it as "e4130 norm aq"... is that what I am looking for?  They also show 4130 hot rolled but don't quote a price online.  Hot vs Cold... does it make any difference?  Am I liable to be taking a trip to Chino after talking to a machine shop up here?

[GGaskill]

Let me contact one of my usual metals suppliers and see what they want for a similar piece or a similar piece of 4140.  $140 seems too much for that piece.  Do you really need a 38" piece?

There are at least two differences between hot rolled and cold rolled.  Cold rolled is clean on the outside so you can use pretty much the whole diameter whereas hot rolled has scale on the outside which must be machined off so you usually can't use the nominal diameter.  Also, cold rolled is full of the stresses of cold rolling which usually makes it a little stronger than hot rolled but it also has a tendency to move around as the stress pattern is altered by machining.

[Evil Dog]

The bore itself measures 30 3/4" deep and looks to have a square bottom.  I am guessing that a somewhat longer piece would be necessary for machining... something for the lathe jaws to grab ahold of.  I am presuming starting with 2 1/2" rather than 2 3/8" to assure enough material to turn a liner that is actually round.

[dominick]

Evil Dog,  Here's a suggestion for you..  If the existing liner is thick enough, then have it bored to 2 1/2" to fit a piece of 2 1/2" .120 wall chrome moly.  Inside of the 2 1/2" moly will slide [10 thousands clearance] 2 1/4" .250 wall moly with the plug TIG welded in place.  The 2 1/2" moly is about 9 dollars a foot and the 2 1/4 .250 wall stuff is 14.90 a foot.  Approximately 75 dollars  in material plus shipping.  Here's the source: Dillsburg Aeroplane Works, Ph# 717- 432- 4589 Charles Vogelsong.  This of course depends on the thickness of the existing liner. I would make sure to find a machine shop that can bore the barrel.  I have had trouble finding someone who can bore that ID and length bore.  Then leave the 2 1/2" moly about 1/8" short and this will give you a gap to weld at the muzzle.  The ID of the 2 1/4" tube is 1.75",  Golf ball size..  Dom