From reading, they appear to have an hrc of around 50-55. Using a regular drill press, what advice can y’all give on what bit / jogger to drill and tap? Any recommended taps suitable for such a hardened steel?
Thank you.
If you have to ask, you probably shouldn’t. Sorry but as a machinist cutting something that hard is a pain even with carbide tooling and solid workholding. It’s not something I would want to do with a drill press and hobby tooling.
The good news, if you decide to go ahead. Carriers are only surface hardened. If you have a carbide spot that can break through, you should be able to use a regular drill and tap. Go slow, use lots of oil.
What exactly are you drilling and tapping? Did you break off a gas key fastener?
Sometimes you just need a hole in a carrier, man!
Now I’m thinking he’s building some type of side charger
In that case, this thread would need to be transferred to ARFcom!
True story. When I was in the process of researching my first can I reached out to Otter Creek and asked about their warranty policy. The response was “We will fix any damaged can no matter what. Unless you do something REALLY stupid like take a hand drill and try and make a 30 cal can out of a 5.56 can.” I said that is far too specific for you to have made that up. He said, “it’s happened. We charged him $200 for being dumb.” LMFAO. The thought process around that event is the ultimate Bubba.
That’s called the stupid tax, lol
Will try and help answer, vs knocking your question.
Asking questions is for doers. Can’t become a doer without asking questions.
You said BCG, so I will assume through hole.
In the realm of C158 or 9310, cobalt drill bits will work.
Setup and cooling is also key. I prefer a flow of cutting fluid to cool and remove chips.
Holding the piece tight in correct geometry is imperative, so it needs correct vice and maybe a mounting jig of some kind, what that jig is varies.
Spotting the location is a good 1st step, a carbide spotting bit is ok here.
For a through hole, and depending on size, but lets say 1/4", I would perhaps start with 1/8" then finish off with 1/4" piloted cobalt.
Must use drill size specified by the tap being used.
All that said, it assumes a decent press with tight quill bearings.
So in general, good setup, cutting/cooling fluid, correct bits and procedure, and slow speed with medium’ish pressure.
As for tapping, it’s a slow procedure. If you can find an undersized tap, that would be best. Grainger or McMaster for those. Cutting oil and very short turns by hand, 1/8th turns would probably be pushing the limits by hand. Cut a little, back out some, every 1/4 turn (90deg) worth of cut, back it all out, clean it all, go again.
Again, it’s a very slow process.
I asked what exactly he was drilling and he never responded, so not exactly knocking anything. There is absolutely zero reason to drill into a carrier. Zero. The only possible reason would be if a fastener broke off and had to be drilled out. There’s no need to encourage and educate someone on how to compromise the integrity of a critical firearm component by doing doing something ignorant.
You said “zero”, twice, but then gave a reason.
There are two other possibilities. Trying to make a sidecharger, and experimenting with reduced mass using existing parts. I think both are bad ideas, but I have attempted one of them. Unsuccessfully.
This isn’t a particularly dangerous endeavor, just not a beneficial one.
One well known reason to drill holes in a carrier is to pin a weight in place. Like adding weight to some of the odd calibers to slow down bolt speed. It’s done more often than you might think.
You are one of the few here that actually has a clue sir… 
Quite curious as to how this turned out. Id be comfortable drilling the hole in a B port that’s in good shape but tapping by hand would still make me nervous even using the machine for tap alignment. On all but the absolute best made drill press, with the table trammed and good spindle bearings I would be expecting less than optimal outcome.
IMHO the best way is to find a local job shop or small machine shop with a CNC mill and ask (or beg) them to drill/ thread mill. Rigid machine and high spindle speed with carbide drill and carbide thread mill would make really quick work of it. Shouldn’t take long to program either.
The hole is drilled and tapped but I am still waiting on another bit to create a level mating surface for the handle end. I hope to have it done in a week or so! So far it’s been easy. Hopefully I won’t destroy the upper or injure myself.
Great success!
How did you end up doing it?
A stub carbide drill bit that was, I think, 4.2mm. Then worked in the tap by hand. Just using a home drill press for the drilling and cutting oil and patience. I believe the bolt carrier is either an unmarked Aero or an unmarked ToolCraft.
Can you or anyone else think of a clearance issue? I’m going to cut a slot for the handle reciprocating. I can’t think of any other problem. Likely going with a single use crush washer for the handle.
That’s bolt material, carriers are 8620