How did I mess up this "crooked" drilling?

[Desolus]

Iv'e had some limited experience in making gun barrels and since no one here has mentioned making your own D bit I thought I'd mention it. In the past what I have done is use a round bar and grind(with my tiny bench grinder and belt sander), then polish a D bit cutting surface onto the end of it and taking the drilling very slowly. Then use a reamer to take the cut to final depth. In my case followed by a rifling broach. This worked for me on pistol barrels using a less than new lathe I had access to at the time.

If you'd rather not make a bit, I have purchased gun drills from eldorado tool and they work fine.

 

[EmilioG]

Makes me wonder how they made a Henry Rifle back in the old days. A precision octagonal barrel with a straight bore.

 

[RJSakowski]

A local blacksmith made a number of flintlock rifles. The barrel was made by coiling 1/2" x 1" flat stock and jump (forge) welding the coil into a tube. The tube was straightened with a mandrel. drilled using a homemade gun drill and reamed. The rifling was then cut and the exterior of the barrel was then finished to an octagonal form on a Bridgeport. As I recall, he was self taught, having examined a number of historic pieces to figure out how they were made, and his method deviated from the traditional methods.

"The Modern Gunsmith" by James V. Howe (1934) has a good section on barrel making tools. It also has some good information abut machine shop topics in general. It is available for download on line if anyone is interested.
https://archive.org/details/The_Modern_Gunsmith_Vol_1_Howe_1941
https://archive.org/details/The_Modern_Gunsmith_Vol_2_Howe_1941

 

[EmilioG]

http://www.firearmsid.com/feature articles/rifledbarrelmanuf/barrelmanufacture.htm

 

[Bill Gruby]

I'm going to swap methods. In tubing I would never drill, it's time to bore the hole. The slightest imperfection in the original bore will throw the finished drilled bore off. A drill bit will not correct imperfections, boring bars will. Just my way of doing things.

"Billy G"

 

[owl]

A local blacksmith made a number of flintlock rifles. The barrel was made by coiling 1/2" x 1" flat stock and jump (forge) welding the coil into a tube. The tube was straightened with a mandrel. drilled using a homemade gun drill and reamed. The rifling was then cut and the exterior of the barrel was then finished to an octagonal form on a Bridgeport. As I recall, he was self taught, having examined a number of historic pieces to figure out how they were made, and his method deviated from the traditional methods.

"The Modern Gunsmith" by James V. Howe (1934) has a good section on barrel making tools. It also has some good information abut machine shop topics in general. It is available for download on line if anyone is interested.
https://archive.org/details/The_Modern_Gunsmith_Vol_1_Howe_1941
https://archive.org/details/The_Modern_Gunsmith_Vol_2_Howe_1941

Also, if you look at the old manuals, you will find that after reaming, but before profiling, they typically stretched a cord or wire through the bore, on a simple bow to tension it taut, then looked through the bore at the light pattern and used those patterns to figure out how to straighten the bore with a machine that pressed at a particular spot. This was considered a high skill that took years to master. After the bore was straightened, and the outside was profiled, they generally did it again, as the profiling could warp the bore. Even then, some barrels would move point of impact as they heated up, while others would not.

 

[Silverbullet]

Are your headstock and tailstock in good alignment with each other?
Mark S.

So many times I've seen and helped with holes not drilling straight , yes drill bits will and do wonder but not that much usually. Many drill bits will drill oversized even undersized if the bits not sharpened correctly. They get bent ,,yes bent,, that accounts in many cases. Times it's the alignments of the head and tailstock. Even wear in the ways will affect the drilling straight holes problem . Simple fixes make sure the LATHES in alignment. Then that the piece is turning true in the chuck or collet , even after all that take the precaution to drill halfway turn the part end for end and drill from the other. Still it can wonder , for really straight holes drill smaller and bore to size. Just seems it's about the only way to somewhat guarantee a true hole.