the straight barrel is exactly that - straight along its entire length. some (pretty rare) are tapered, with the breech being bigger than the muzzle. 'swamped' barrels are thick at the breech, thin out at the waist, and flare out slightly at the muzzle. check out the barrel profiles at the Track of the Wolf website.
the rifling is what imparts the spin to the projectile and keeps it on a more uniform path to the target. if you have conventional rifling, the bottom of the groove is flat, but with radius groove rifling, the lands (high spots) are flat but the grooves are rounded. the advantage (to my mind anyway) of this method is that there are no nooks and crannies for fouling to build up, and the barrel is easier to clean.
(polygonal rifling is different: the entire shape of the bore is not circular, but forms a polygon. for a good 'quick and dirty' on how this works, check out this u-tube:
https://www.youtube.com/watch?v=2O84B700Li4
this is a centerfire thing - don't worry about it if you want to shoot muzzle loaders)
then there's 'progressive' rifling, where the rate of twist changes as the projectile goes down the tube. pretty rare and, although it sound pretty cool, I don't know as its advantages outweigh the extra expense. I can't remember if Charlie Burton does this, but if you're curious, you might want to shoot him an e-mail.
http://fcibarrels.tripod.com/
here's the bad news: galamb is right, you need to get the barrel and the stock pretty much together, so you can keep the barrel in the channel as much as possible. if this is out of your budget, get the barrel first. Pecatonica has very nice precarves at reasonable prices - here's a link:
http://www.longrifles-pr.com/
don't make mistake I almost did- be sure that your barrel channel will fit the profile of the barrel you use.
:redface: :redface: :redface: :cursing:
I would also recommend that you get a copy of Recreating the American Longrifle (another link:
http://www.trackofthewolf.com/Categories/PartDetail.aspx/321/1/BOOK-RAL
or a copy of Peter Alexander's book, The Gunsmith of Grenville County:
http://www.trackofthewolf.com/Categories/PartDetail.aspx/321/1/BOOK-GGC
both of these books are about forty bucks, which seems pretty steep, but they will save you much more than their cost in parts you don't spoil and time you don't waste on waiting for the replacement to arrive. I like Alexander's book better, but that's just one guy's opinion, and probably worth about what you just paid for it.
more bad news: the project upon which you embark is just your first, and there's no twelve step program for
this addiction.
...seriously - good luck with your build, and take pictures ... we love pictures...