I'm trying to drill a clean hole into a bullet shell casing

Not sure if this is the place to post but any help is appreciated.

I have a project in working and want to make a cord lock out of two bullet shell casings. The smaller caliber bullet I’ll be using is .45 and I’m drilling a 3/8in hole using a drill press. I’d like to drill all the way through from one side without needing to rotate the casing to drill from the opposite side. I’m looking for advice on how to drill the hole as clean as I can because right now the side the drill bit exits is jagged and would take extra work to fix. Is there a special drill bit I can use to not have jagged results? It’s a bit challenging because it’s a cylindrical shape.

I was suggested stepped drill bits at the local hardware store, but if I use those I’d have to rotate the casing to get the same sized hole on each side. I tried these bits thinking they would be the ticket but no luck: https://a.co/d/afZh4k8

Drilling a hole that size through the casing is going to be tricky because as you discovered the thin brass tears very easily and 3/8 is quite a large hole relative to the diameter of a .45 casing. If you can clamp your work in a drill press vise and go very slowly and carefully you can drill the hole by using a 3/8" end mill, preferably one with a high flute count, instead of a drill bit. Another option would be to drill clean through both sides on the drill press using a small drill bit, say 1/8", and then open those holes up bit by bit using the step drill. If you are having trouble with the step drill catching an alternate method is to start with the small hole and then gradually enlarge them with a tapered reamer and/or needle files.

A few thoughts

  1. When cutting thin metal - the issue is often the sharp edge of the intersection of the drill bit flutes and the bit tip. That same sharp edge that helps the bit grab and cut a thick piece of iron or steel also grabs the thin sheet metal too much and you end with a ragged cut. You can modify tour bit with a file or hone/stone to flatten that cutting edge.
  2. you probably need to support the backside of the cut. With a bullet casing - you might need to find a suitably sized dowel to support the first (top) cut and then a piece of wood with a groove to match the casing for the bottom.
  3. An old machinist’s trick for cutting sheetmetal was the use of a wad of cloth - a scrap for some smooth cloth folded over a few times to be about 3 or 4 times the diameter of the hole to be cut. Start the cut on the drill press - with a light touch - just dimpling the metal. Then place the cloth wad over the cut and finish drilling with normal pressure.
  4. You might try #3 in 2 steps - one with a small diameter pilot drill - then the 3/8
  5. Another approach would be to try and find both a dowel to support the inside of the casing and also a thicker tube/pipe to sleeve over the outside - thus supporting each side of the cut

fred is correct that the best way to do this is to fully support the thin case wall, but the trouble is that’s not so easily done at home. If I were doing this I’d ream a hole through a block of scrap aluminum or brass that the casing fits into with a tight slip fit. Then fill the inside of the casing with a low-melt alloy like cerrosafe. Drill through the entire assembly, press the casing out of the block of scrap, and then melt out the cerrosafe with boiling water. That’s easy in a machine shop with all the materials lying around but probably isn’t practical for a DIY project.
It might be possible to sand a piece of dowel to fit tightly inside the case, that could support the inside while drilling.

if you mean a brass cartridge that is empty, I would get a dowle or some other moderately stiff material to put inside and support the bottom and then I would drill it from the bottom into the dowel piece. using a new dowel with each casing.

also covered your other sizes the same way - different dowel. you might consider filling the case with wax as an option. but I think you need more to hold with.

another option would be to drill though the casing from the inside hole and putting the base on a sacrifical piece of wood or even sheet metal so you could sandwich the brass with something stronger so the drill runs through it and burnishes it as it goes though the next material. and I might start with a 1/4 and then finish with a 3/8 - not sure if that would help.

I suppose you could imbed the entire casing in something, so it’s supported inside and out. I’d guess you’d want one end of the casing to stick out slightly, so you see where to drill.

Re the supporting material, it could be a low-melting metal or wood like the others suggest. But I wonder if plain plaster would work, or some other stiff, nonshrinking filler material. The stress loads won’t be huge, I imagine. If it weren’t difficult to remove, I’d suggest epoxy.

Another thought is to use the smallest cutting teeth possible, to avoid grabbing and tearing the brass. And I guess you’d find the smallest teeth are on abrasive wheels. So you might look for a conical grind stone, like the ones made for dremels or die grinders. Drill a pilot hole first to give the stone a start and go slow. I see Dremel offers a 3/8" diameter stone. 952 Grinding Bits | Dremel

The last idea I have is to use a piece of thin-wall 3/8" tubing mounted in a drill press as a cutting tool, along with some fine abrasive paste to do the actual cutting. Maybe you could cut a few notches into the edge of the tube as reservoirs for the abrasive.

Bear in mind I haven’t tried any of these methods, and I don’t know crap about the subject. :wink:

Plaster is abrasive, it will dull the drill bit instantly unless you use a carbide-tipped masonry drill, but that won’t leave a clean hole in the brass. Plaster is also difficult to remove after you’re done. Hard wax may work, the kind that jewelers use for making patterns. Epoxy is not a bad idea. It can be removed chemically from metal using a product like Attack:

…though that’s some pretty nasty stuff, so make sure you have PPE, and you will need a small glass or metal vessel to soak the parts in as it will dissolve most plastics.

You have the right idea with using the smallest cutting teeth possible but abrasive stones are a poor idea with brass or aluminum, the stone will load up with the soft metal and it won’t grind anymore. All newbies in the machine shop try it exactly once and then get their rear end chewed off for clogging up the wheel, requiring it to be re-dressed.

The low melting point metal alloy idea might work. There is Wood’s Metal - but that has toxicity issues. You might look for Fields Metal - but be prepared to pay for its indium content.

wax might be plenty also which casing.

45 acp or 45 long colt. IE does it have the primer pocket or flot bottom. 45 acp would be potentially easier as there is the primer pocket to push out. IE there is a hole in the bottom to start with.

OH another thought - use a punch.

Aha! Somebody who actually knows his sh*t, unlike me. Thanks for the corrections and comments.

I know plaster is abrasive, but it might be worth using up a bit or two for this particular job. Same with using an abrasive stone (which I didn’t know would be clogged with brass.) The stone would clog, but you could pull it back and clean it with a dressing stone.

But perhaps wood filler would work as a filler material.

And there’s still the idea of using a piece of 3/8" tubing as a tool, along with an abrasive paste. And I wonder if there isn’t a hole-cutting bit, just a piece of tubing on a shaft, made of diamond-impregnated steel.

And my last, craziest idea is to use electrical discharge machining. But I know even less about that than I do about anything else. :slight_smile:

There are tubular hole-cutting bits with diamond abrasive on them, for example:

I have only ever used those kind of things on stone or ceramics. It certainly might work, though I would be concerned that the brass might load up the abrasive the same way it loads up on grinding wheels, though I’ve never tried: It’s worth a shot: go very slow, frequently raise the bit to clear dust, and have plenty of water in a squirt bottle to wash away dust.

You also just gave me another idea: there are special tools used in auto body shops to remove spot welds, they are basically a tiny hole saw. If memory serves 3/8" just so happens to be a common size for these. Random example:

Perfect! They seem designed to do exactly what the OP wanted (though they don’t have brass in the list of suitable materials.)

I’d imagine you want high RPMs and slow feed rates.

I would still worry about tearing as the bit begins to finish the hole. The cartridge case is pretty sharply curved, and that bit would begin to enter and leave the thin brass at increasingly oblique angles as it goes deeper.

Here’s another crazy idea. Don’t drill directly into the brass casing. Instead, press the side of it against the side of a cylindrical cutter or grind stone of some kind (similar to a straight router bit). If the cutter is the right size and if it doesn’t dig too deep, it will bite out something that looks like a circular hole when seen face on. You can then make it a perfect circle with a hand file or something.

I used to have enough math to figure out the intersection of two skew cylinders, and then graph a projection of that curve, but I don’t now.

There’s no doubt those tools can cut brass, if they can cut steel then they will easily do brass, it is super simple to machine. In fact people often do “dry runs” of machining fancy parts made out of expensive or tougher materials first by machining them in brass first, that way if there’s some problem with your G-code, machine setup, or whatever else, you have less risk breaking tools and if the part comes out bad you’ve ruined a piece of brass, not some high dollar superalloy.
High speed slow feed would be optimal. This would be easy in a milling machine where you have a fine feed handwheel to apply the cutter to the work (and and end mill is much cheaper than a spot weld cutter), but it’s going to come down to the skill of the operator with a drill press with just a quill handle. Like you said, when the bit clears the the hole it could catch and tear if fed too fast.

I like your idea of using a round file from the side of the casing. Once you got your hole started it would be easy to finish it from the interior with a small round file, like a rat-tail or a chainsaw sharpening file.

Another duh moment: Drill straight through the casing with a small starter drill bit, say 1/8". That should go easily. Then finish it manually with a tapered reamer like:

Brass cuts very easily so I’m sure even a cheapo import reamer will do that job.