There is a pretty good 101 on the Border Barrels site. They've re-instated it after years of absence.
http://www.border-barrels.com/articles/bmart.htm
and a word of warning - avoid buying Harold Hoffman's books, there are links posted in old threads here to download scans of Vickery and of Howe, which are both excellent, and they appear to be where Hoffman plagiarised his information, he also appears to have copied a piece about barrel steels that appears in one of Ackley's handbooks (which are of middling quality IMO), again without citing his sources. Hoffman's contribution to the books in his name appears to consist of poor spelling and grammar, which you could forgive, if he'd only cited his sources, for you to check against.
Steel selection depends on the pressure / velocity of the round.
For black powder, and cartridges with black powder type pressure levels and performance, for example .22lr, free cutting mild steel is apparently adequate.
For higher pressure levels, jacketed bullets and higher velocities, or for lighter weight -where you want to use reduced wall thickness, then the pre hard and stress relieved 4140 seems to provide the combination of strength, wear resistance, good surface finish and price needed, along with taking hot bluing well. I've read widely differing opinions of 1350 (stressproof), apparently it is even freer cutting, but wall thickness may need to be increased to compensate for lower yield strength.
For stainless barrels, 416R (R for stress relieved) provides the strength and free machining. When I was organising a gunsmith to get a one off barrel made by Border Barrels, the smith reckoned that Border preferred to use 416 over 4140, due to the 416 being easier on their tools. Disadvantages with stainless are greater density, and poorer heat conduction. 4 series (martensitic = hardenable) stainless also suffers a brittle transition around about zero degrees Centigrade. In practice, the embrittlement doesn't seem to occur until you are into big negative Fahrenheit figures; something to bear in mind for winter shooting in very frosty weather.
Design assumptions for barrels are that the stress is pseudo static, and that the max allowable hoop stress on the inside of the bore is the yeild stress of the steel! in practice you'd put a factor of safety of 1.5 or so on that.
For air rifles, I've read about amateur builders using free machining brass, as high tensile strength and resistance to erosion aren't needed.
Drilling;
Industry standard would be a commercial Gun Drill, although before Pratt & Whitney developed what we would recognise as a gun drill, people were drilling with D bits of various descriptions, used through hollow centres. There is an article in an air gun magazine describing home barrel making experiments peck drilling with a D bit in a 7" swing Myford lathe. Guy Lautard also sells a DVD showing a home built drilling and rifling machine.
Viktor Astakhov's site has excellent info on self piloting drills and drilling, and he occasionally contributes on PM.
In the past, barrels for the trapdoor Springfields were hot rolled over a series of mandrels, and in the more distant past, barrels were also forge welded from twisted strip, in a spiral.
Reaming:
The Border Barrels article shows a modern multi flute reamer, unless things have changed, I understand that these use Machinery's handbook figures for radial spacing of flutes to avoid chatter.
Traditional methods of reaming used "spill boring" with a square sectioned "armourer's bit" backed up with a whittled piece of bamboo ("spill"), and adjusted by inserting pieces of fine paper between the steel bit and the wooden "spill".
Supposedly, in skilled hands, spill boring could hold tolerances of a tenth of a thou.
Pictures of the style of tool are shown in older books, for example WW Greener's "The Gun", where it is shown in connection with choke boring shotgun barrels. Lubricant was apparently peanut oil. I don't know whether this was for some specific property of the oil, compared to other oils, or whether it was just a tradition that had never been questioned.
Rifling:
single point Cut rifling cutter boxes are well shown in Vickery and in Howe. A search of patents will turn up some later refinements, along with patents by people like Gerlich and Lovely (yes, that is a surname!) for cutter boxes for rifling squeeze bores, and the rifling machines to go allong with them.
Positive and negative rake
There appears to be a lot of repetition of the mantra of "negative rake" for rifling cutters. I can't remember whether it is Vickery of Howe who clarifies this. Apparently both were used. Negative rake was termed "scrape rifling" and removed hundredths of a thou a pass or less, but supposedly gave a better finish than the positive rake "cut rifling", although there doesn't seem to be a problem with cut rifling, there may have been a difference with hand powered operation.
getting a twist
constant pitch rifling is equivalent to the print you'd get by rolling a cylinder over an ink soaked thread layed at an angle, and this was the principle used to lay out the helix for hand cutting a wooden rifling guide, fore runner of the more modern rifling machine in the Border Barrels article.
The helix feed can also be generated by a rack (this is the principle shown in the Lautard DVD).
Both of those are fixed pitch
Faster or slower pitches can be achieved using a "sine bar", which is equivalent to altering the angle of the ink soaked cotton thread, except you can alter it as often as you like.
The sine bar is usually straight, but, if you want a "gain" twist, you can rig up a curved guide. A Lindsay compilation reprint "Ordnance 1900" from a few years back, has an article about improvising gain twist rifling on a large scale, for a shop made artillery piece during the siege of Kimberley, in the Boer War.
Normal practice for single point cut rifling is to index to the next groove after every pass of the cutter, and to advance the cutter after every full rotation of the barrel, that way, each groove should end up identical shape and depth.
Multi point cutters and broaches were attempts to speed up production of cut barrels, well done, they were probably adequate, but as cut rifling is now for the premium market, the cost of the broaches and of maintaining them would be prohibitive, and single point cutting is used.
A micro stepping stepper motor could probably be used to rotate the barrel for generating the helix, and for indexing it too, but old fashioned mechanical means seem to work very nicely, and the poor torsional stiffness of the rod carrying the rifling cutter box would likely limit any accuracy gains for either mechanical or numerical rotation.
Swaged Rifling
Two approaches were developed during the Second World War: hammering over a mandrel was tried in Britain, but it seems not taken to full development, and the rifles with "dollied" barrels were re barreled. In Germany, the system was fully developed to hammer forging.
US developments culminated in Merle H ("Mike") Walker's patent for button rifling, where an over sized hard metal "button" with the impression of the rifling and its twist is pushed or pulled through the the lubricated bore.
Hammer forging, in its fullest form, allows the chamber and throat to be formed in the same operation as the bore.
Either operation will allow the forming of exotic shapes of land and groove, and the formation of many, many grooves or lands - if you want them to.
Both swaging operations induce severe residual stresses in the barrel, this can be used to advantage, for example turning down most of the barrel but leaving a section at the muzzle at full diameter produces a slight choke effect, used in some target rifles. the work hardening may also have benefits in wear resistance, and the residual stresses can be used to counter tensile hoop[ stresses during firing, allowing for a slight reduction on the weight for a given strength (a sort of one piece equivalent to the artillery gun practice of shrinking sleeves on)
For turning to say sporter profile, a swaged barrel would need to be stress relieved first, or the bore would become slacker towards the muzzle.
Cont