Drill bit for gas block pinning on nitride-treated barrel

[SomeOtherGuy]

I have two nitride-treated barrels, one Daniel Defense and one AR Performance, on which I am going to be installing Geissele super gas blocks. The DD will need dimples for the set screws, and both barrels will need a hole drilled for pinning the gas block (the Geissele SGB is one of the newer gas block designs that makes this easier).

The general advice from Geissele and other companies making similar gas blocks is to use a cobalt steel drill bit, but a quick look at hardnesses suggests that a cobalt drill bit is in about the same hardness range (mid 60's HRc) as the nitride surface layer (HRc in the 60's). Of course most AR barrels are either phosphate treated 4140-4150 steel or untreated 416 or 410 stainless steel, any of which has a surface hardness far lower than the cobalt bits (from the upper 20's to mid 30's HRc). Can I still use a cobalt drill bit for drilling the nitride-treated barrels, or should I use a carbide tipped (metal cutting) bit instead? If I go with carbide, is there any change required in technique or bit size to use?

Edit to add: I will be using a shop size drill press, not attempting this with a hand-held drill.

[MarkG]

Carbide is a no-go in hand-held drilling operations. A nitrided barrel is going to give you fits with a cobalt drill. My guess is that whoever is recommending them is assuming 4150 or 416 barrels.

[SomeOtherGuy]

Carbide is a no-go in hand-held drilling operations. A nitrided barrel is going to give you fits with a cobalt drill. My guess is that whoever is recommending them is assuming 4150 or 416 barrels.

I'll be using a floor mounted (5 1/2' tall) drill press for this operation, with the workpiece held in a vise mounted on the drill press table. Trying to avoid WECSOG.

[sickeness]

Mark the spot you want to drill and then use a dremel to break a small divot in the surface and then drill the dimple. I just did this today on an ARP barrel and it turned out great.

[MarkG]

I'll be using a floor mounted (5 1/2' tall) drill press for this operation, with the workpiece held in a vise mounted on the drill press table. Trying to avoid WECSOG.

Might be tough to get X and Y axis alignment but what's a couple of hundredths or three right?

Mark the spot you want to drill and then use a dremel to break a small divot in the surface and then drill the dimple. I just did this today on an ARP barrel and it turned out great.

Photo rule violation...

[GH41]

If he breaks a bit just before getting out of the barrel he'll wish he had sent it out. GH

[markm]

Photo rule violation...

He's talking dimple for set screw I think... not reaming a pin hole.

[MistWolf]

SOG is talking about dimples for the set screw and drilling the hole for the pin

[SomeOtherGuy]

SOG is talking about dimples for the set screw and drilling the hole for the pin

Correct, but I think sickeness was only talking about dimples.

EDIT: I found the info I needed with a google search (I had initially searched just this site with no luck). Carbide it will be, with some special techniques. Thanks Constructor for your informative comments at various sites.

[MarkG]

Is there any downside to using a carbide tipped bit, given that I'll be using it in a full size drill press with clamped workpiece?

A carbide tipped drill requires a spot face and hole to complete the operation. For about $60 you could have this professionally done. I'd pay cash money to be there to see you f' this up.

Pictures every step of the way or it didn't happen.