Octagonal barrel questions...

[Typecaster]

1. How precise does an octagonal barrel have to be? I have an indexing faceplate on a heavy-duty wood lathe, and was thinking of mounting a grinder on a carriage to grind the flats (very slowly, to prevent heat distortion). In effect, it would be like using a surface grinder—take a pass, rotate 180º, take another pass...

I know the old muzzle-loader barrels were shaped using a file, pre-mills. (I have a schwamped Damascus barrel that had to have been welded around a mandrel, then filed to be an octagon. The rifle is dated 1842, and was converted from flint to percussion—the frizzen spring is still there. I used to shoot it, and it was very accurate.)

2. Common sense tells me that if the flats are not concentric with the bore, the barrel is not going to heat up evenly. I've also read that barrel blanks are not always concentric, so would a non-concentric octagonal barrel be any worse?

Am I over-thinking this?

Richard

[John Taylor]

Muzzle loading barrel were forged octagon during the welding proses then filed smooth. To file that much metal off a round barrel would take a long time.
Grinding an octagon shape would take a long time also. I tried to use a surface grinder on a barrel that was already octagon to take out the machine marks. Bad idea. As the metal heats up it expands and bows the barrel toward the grinding wheel, even with flood coolant.
Octagon barrels that have the bore off center at one end were octagon before drilling. The drill starts at the center of the barrel but doesn't always end up in the center at the other end. Barrels that are machined octagon after boring should have the bore in the center.
I will machine octagon a barrel up to 28" long for $100.

[leftiye]

I'd get as accurate as you can. No use to take chances with the dimensions causing warpage. If your lathe's bed is straight, then possibly the grinder approach on the carriage might work. As grinding takes a lot of time, and as it produces a lot of heat, you're gonna be at it for a while! The first two flats can be milled on a milling machine by clamping the barrel to the table (first cut in a T slot groove between surfaces). So doing it on a mill is vastly easier. After that all you need is a couple of 45 degree blocks to align the angle correctly for suceeding cuts. Virtually no heat if a coolant is used.

[KCSO]

Accurate is theoreticaly better but... I made a load of Muzzleloaders from barrels that were off center. You put the high side to the bottom and use less front sight. Since several of those rifles would shoot championship groups at 100 yards I can't see that there is a huge problem here. Heat distortion, huh, how fast can you load a muzzleloader? In demonstrations i have done 6 shots a minute, in a match you are shooting one shot ever 2 minutes, maybe. Yes for asthetics I prefer the best barrel i can get, but even a barrel 10 thou off center is probably better than anything they turned out from forge welding and filing. I have taken apart and examined a whole load of old rifles and i now have in the shop an original Southern Rifle with a 48" barrel. Guess what, if the hole in the middle was straight the outside didn't matter that much. I have seen several swamped barrels from the 1780 period that were octagon on the top and ground round on the bottom for ease of inletting.

Some of the old barrels were ground to shape but NOT on modern machinery. Take a water wheel 4 foot around and spin it slow and you have a whole 'nother field of endevour. I know a well nown maker in Texas that use to profile his barrels with an Auto body grinder and then finish with a draw file. I bought some of Bill Large's old tools and have used his barrels and i can tell yu that compared to say, a new Green Mountain, they looked rough, but they sure shot good. I'll let you in on a secret, a lot of barrrels today aren't even straight. Most folks could'nt tell a good straight tube from a crooked one, but even the crooked ones shoot just about as well as a man can hold for off hand iron sight shootin' (4" at 100 yards) Now if you want to talk under 1/2" at that range THEN you are in a different ball park.

Give it a try on your equipment, you might be surprised at how well it comes out, AND you will learn a LOT.

[Wayne Smith]

You weren't planning to swamp it, were you? The old barrels were made with a billet that was thicker on each end and thinner in the middle, the swamp was in the billet, not filed in. The gunsmith at Williamsburg, VA had a good display showing the process several years ago when I was last there.