how does one create a round bottom Octagon barrel?

[greywuuf]

I have in my mind to do a reproduction of a 1803 Harpers Ferry rifle, and some of the research I have come across states that the earlier rifles we more of an English Sporting rifle persuasion, and they had a lighter underlug and a round bottom ( reported to be weight saving) to the octagon section, I have a round Blank and it seems as though the Correct way to do this will be to file the first 12" ( about...) to Full actagon and then  finish profiling the bottom round.....as compared to only filing the top half octagon in the first place....   Can any of you shed light on what oringinally occured  and how I might go about duplicating this  starting from round stock instead of ( I am assuming) an octagon barrel ?

[rich pierce]

I don't have any factual information but I might not assume this was for weight savings.  It's possible the barrels were made then turned round then flats filed on the top 5 sides at the breech end of the barrel.

[Acer Saccharum]

Just fresh from the 'thinking-out-loud-Dept':

If you have uneven walls on the barrel, you might get uneven expansion of the tube as it heats up from firing, like the barrel might bend a little. Then it would return once cool.

This would show up as a vertical stringing on the target, assuming you'd like to hit your target on a regular basis.

Above thoughts not based on experience.

[rich pierce]

Good thinking Acer.  Probably this would have greater effect at the muzzle end if the barrel is tapered?

[Daryl]

Just fresh from the 'thinking-out-loud-Dept':

If you have uneven walls on the barrel, you might get uneven expansion of the tube as it heats up from firing, like the barrel might bend a little. Then it would return once cool.

This would show up as a vertical stringing on the target, assuming you'd like to hit your target on a regular basis.

Above thoughts not based on experience.

YES - this makes perfect sense - as in, if you were shooting in a competition with the rifle, the change in poi might cause problems - maybe not much, maybe serious.

For a hunting gun, always shot "cold", this would not be troublesome - but with different seasons, ie: different temperatures might cause different points of impact for that first shot and of course if shot until hot, they'd walk up the target.  

Now, all this theory noted, we also know an octagonal shape is stiffer than a round shape. Due to being less metal on the top surface, with more metal on the bottom (not filed off to octagonal shape), the barrel should warp or bend upwards. Due to the stiffer nature of the octagonal shape, it is possible the top flats would resist the upward bending and there may be NONE at all - or little - certainly less than a smaller rounded surface - an interesting hypothesis.

[Old Ford2]

Hi.
Putting your barrel in a lathe, with a four jaw chuck, you can off center the barrel, turning off the corners of the flats only on one side as desired.
You would also have to off set the tail stock the same amount to get constant results. ( ie: 1/8" at both ends. )
Very simple to do!
Fred

[Acer Saccharum]

Why not buy a barrel that already has the right configuration?

[smart dog]

Hi Tom,
Wouldn't uneven heating and cooling always happen because 1/2 of a barrel is exposed to air and the other is nestled in insulating wood?

dave

[Acer Saccharum]

Smart dog, you have a point. That is surely the next excuse I will use when I can't hit the target. 

[greywuuf]

Why not buy a barrel that already has the right configuration?

Really ?   why not just commision the piece to be built?

 I only bought a round blank because I have not  gotten around to building a rifling and boring bench yet, and wrought iron is hard to come by in Alaska and I did not weld up my barrel ( yet )

[Acer Saccharum]

why not just commision the piece to be built?

Seriously, it's very hard by web(the typed word) to determine where someone is coming from. Had I known you were going to weld up your own barrel, I would have had a different answer. One of the things that gets lost on the web is the interpersonal communication that there are no words for. Body language, facial expression, etc, is just missing. So no hurt or offense intended.

[greywuuf]

Acer,  I am sorry. My reply came out a lot "Snarkier" than I had intended.  I am just tired of "Catching heat" for this build. ( it is being built how I want it and not PC ... I just happen to have a pretty piece of maple and I want an 1803 )
I thought the half round half actagon was a fairly common profile and even in my very limited experience  the round on the bottom of the octagon part seems at least well known if not common.  I said I had a round Blank and wanted to do that, I did not really expect to get all the theoretical reason why it is a bad idea .  I dont recall anyone ever hearing.." man why would you do releif carving on a barrel, that wont help you win competitions..."   anyway, just trying to decide if I should go complete octagon and round half... or if I should just file flats on the top half.

[shortbarrel]

Saw a round bottom rifle, with the top five filed many years ago.The round bottom was just  hammer forged and hit with a file to take off the high spots. This was a southern mountain rifle. Made to feed the family, not shoot targets.

[smart dog]

Smart dog, you have a point. That is surely the next excuse I will use when I can't hit the target.  

Hi Tom,
You are welcome.  If you need any more excuses for poor shooting just call me.  I am right next door in Vermont.

dave

[Acer Saccharum]

I am just tired of "Catching heat" for this build. ( it is being built how I want it and not PC ... I just happen to have a pretty piece of maple and I want an 1803 )

That's a really good thing to know, that you are building to please yourself. I think too many folks get caught in the trap of building for others.

I know this site is about traditional longrifles, so yes, there is a certain 'bent' to the site already. You will get heat if you post photos of a purple pistol gripped muzzle loader. As a moderator, I try very hard to encourage the traditional side of the longrifle, without making non-traditional builders feel unwelcome. I had no intentions of giving you heat, but I was trying to offer a practical solution.

But by now, I have learned you are in Alaska, and barrels are not easy to come by. So I better appreciate your making what you have work

[greywuuf]

Thank you Acer,
I dont know why I am so defensive..... I really put a couple of years of thought into this gun, and it is my First NON kit build, and as a 1803 I know it falls out side of the forum topics. The deal is I have found through various traditions kits and restocking garbage "originals" obtained from Gun Broker, that I will spend a great deal more time actually USING  a smoothbore.  Big game here in Alaska ( that is suitable for Muzzle loading and accesible to me ) is limited to Moose and Caribou... meaning I would get one hunt a year ( if that )  whereas small game ( Hares and ptarmigan) are an easy day trip for most of the year. I am Not a shotgun guy, and am not a wing shooter ( which is ok ptarmigan and hares are normally hunted with a .22 ) ....So I have settled on the 1803 as something I like the looks of, has a large barrel channel that i can put a smoothbore in and will make me happy and be "usefull" to me. I am also a incurable Do it myself kinda guy and the ultimate goal of Owning this weapon is probably not as important as just the act of building it.  I have made enough camp cookery, hooks and flint strikers thatI feel I can  handle the blacksmithing of  iron fitting ( again not something an 1803 has.. but mine will) and if I fail miserably  I have a plasma cutter and a tig torch ....To that end the weird old $#@* that I put together earlier has a half round half octagon, with wedding bands and flats ONLY on the top.   I have a nice smoothie blank in hand and I figured I can start in on the profiling ( large sheldon lathe standing by if I fail miserably at extended draw filing )   I am just trying to determine if I should octagon the entire back half  and then Further cut the bottom half to round... or if I should just go flats on the top


I had hesitated going into details on the gun because it is so non conformist and it is well outside of the long rifle realm.

I guess what I am essentially building is a Northwest trade gun, shaped like an 1803.. because I like that.

Thank you all for hanging in there with me.

[Acer Saccharum]

A few examples I have seen, the barrel is taller than it is wide.

The extreme flare, or 'hump', at the breech seen in profile is NOT carried int the side flats. In other words, if you look straight down on the breech section, the flare is not so pronounced. That means there is more metal on the top three flats than on the sides. no?
From the Hauschka fowler in the Metropolitan Museum:


In an English coach gun, the round barrel is filed flat on both sides to accommodate the lock fit-up, and make a gap-free inlet into the breech.


Offside of lock, where you can see the wedding bands die out because of the flat filing:

[JCKelly]

If you take a round modern made barrel blank and make one side octagon it will bend.

It WILL bend.

If that troubles you, do not do it.

The reason it will bend is that modern muzzle loading barrels are all made of nice cold drawn round bar. The bar, whatever the grade, will have residual stresses in it. I think they are tensile near the outside, balanced by compressive at the bar interior, but I would bow to the knowledge of a steel mill bar guy on this.

Anyway if you take off more metal from one side than the other, you unbalance these stresses and the bar will bend to get them in balance again.

Honest.

All bar is full of residual stresses, if nothing else, from the straightening operation.

Only bar for MODERN barrel making would, or should, be sold thoroughly stress relieved.
This is a detail which may not be of concern to the 12L14 set.

So I am a metallurgist and I know this sort of stuff, OK?
Nevertheless the first time I filed a swamped octagonal (miniature) rifle barrel of some cold-drawn round steel tube the end suddenly bent on me.
Aaagh.
Ever hear of the shoemaker's children?
Anyway no big deal, I wasn't planning on target shooting with elves so I heated the end with a torch to just barely glowing, let it cool, hammered it straight and problem solved.
Solved for me, but this approach won't work on a full size barrel from which you might expect some degree of accuracy. 

Harpers Ferry barrels were hot forged (forge welded and forged to rough blank shape) and then annealed. There would have been very low, if any, residual stresses in that barrel blank.

[Acer Saccharum]

Oh, yeah, the time I tried to turn a barrel down.

I turned some, and it ran out a little, no problem, I'll turn it true with light finishing cuts. Well, I kept trying to get it fairly straight by turning a little more, and a little more, and dang this is taking a long time. When I took it out of the lathe, the bore was so crooked, that I couldn't see through it ( just light coming from the end of the tunnel! ).

What greywuuf is doing won't cause a noticeable difference in the bore, because it will be in the heavy breech area. If it bends, he can file the opposing flats to get it to straighten out.     

[greywuuf]

ok great, now I have to build a 40" heat treat oven and get out the V blocks and lead hammer.

[JCKelly]

Yeah, that's the idea. And a bowstring through the bore to highlight the bend. No problem.

[Acer Saccharum]

In short, if you take metal off one side, and the barrel looks bent, just file off same amount off the other. It will straighten out again.

[Jim Kibler]

A couple of points...  I don't believe it's accurate to say that all modern muzzleloading barrels are made from cold drawn material.  I'm almost certain Ed Rayl uses hot rolled bar.  Rice also performs a stress relief heat treatment on their material.

[Bob Roller]

Jim, I just looked at 8620.According to the info,8620 is HOT rolled and Cold finished up to 12" in diameter.
It is easy to machine and I made several breech plugs from it in the last three years.
 Bob Roller

[Jim Kibler]

About any steel can be either hot rolled or cold drawn.  I believe Ed told me he purchased 8620 that had been hot rolled and not cold drawn.