Drill bit for gas block pinning on nitride-treated barrel

[constructor]

Drilling a round surface when over on the edge of the round is tough. We use a 1/8" carbide end mill at high speed then feed it very slow. Do not pressure carbide bits like HSS ones, it will snap a $40 bit in a second. We drill through 1 side of the gas block and into the barrel enough to make a flat spot. At that point you can swap to a HSS 1/8" bit to finish the hole. I would not drill all the way through with the carbide end mill it will snap off when breaking through the far side.

[SomeOtherGuy]

Thanks, Harrison, exactly the info I was looking for.

[sugerwater]

I've done this type of work for over 40 years, I worked in the top end of the tooling trades in the rust belt my whole working life. Find a local machine shop in your area and talk to the manager or better yet, the guys in the shop. Most are gun people and some will help you out for the experience. Precision work requires a little more then a drill press. A Bridgeport type mill would give you options to indicate, and position tooling and mill a spot to start the hole. If you decide to go it alone, go slow (rpm) and use a cutting fluid. Use a starter drill, or grind a spot though the coating and a Cobalt drill bit or three to drill through. Clear the chips and keep the tool wet. Your big problem will be controlling the feed rate when the drill brakes though. The Cobalt drill will cut though the Nitride with out problems. If the block you are installing has no hole, your job will be much easier as the drill will not fall into a void and only cut on one side. This is hard to explain as it's an operation that requires some knowledge of machining. If your block has a through hole, you will have to mark and spot face (dermal out a pocket) on the barrel, drill the hole, and ream both parts together for a tapered pin . Good luck. If your in the Willoughby Ohio area drop me a pm.

[JChops]

I just did three of the Geissele SGBs (Nitride) following Geissele's instructions to a T and had no problems of the slightest. The cobalt drills work fine.

You didn't say if you have the regular or nitride SGB, but the nitrides are less forgiving during the pinning phase because the hole is already the exact size it needs to be from Geissele. I used the exact cobalt drills from McMaster that Bill recommends for both the dimpling and the rollpins (two different sizes) and they all went through like butter. One of the barrels was a nitrided DD barrel and I noticed nothing different from the two BCM BFH barrels during either phase.

Use a good drill press. As with everything, the hard part is the setup and making sure they are square. If you get that right and have any common sense with machining regarding measurements they will be perfectly aligned like mine.

[MarkG]

I just did three of the Geissele SGBs (Nitride) following Geissele's instructions to a T and had no problems of the slightest. The cobalt drills work fine.

You didn't say if you have the regular or nitride SGB, but the nitrides are less forgiving during the pinning phase because the hole is already the exact size it needs to be from Geissele. I used the exact cobalt drills from McMaster that Bill recommends for both the dimpling and the rollpins (two different sizes) and they all went through like butter. One of the barrels was a nitrided DD barrel and I noticed nothing different from the two BCM BFH barrels during either phase.

Use a good drill press. As with everything, the hard part is the setup and making sure they are square. If you get that right and have any common sense with machining regarding measurements they will be perfectly aligned like mine.

Can you show us some detailed pictures? I'd like to see the barrel (post drilling) in particular. Thanks

[Topgear]

I drilled a Phantom 5C2 for pinning, dimpled for pinning the Phantom, and dimpled for gas block set screws on a nitrided barrel with a cobalt bit just the other night. Worked perfectly. Keep the bit speed down, and lube. I had my doubts as well that I would need carbide to break that surface.

[Donut]

The instructions for the Black River Tactical MicroPin kit say that a cobalt bit will go through Melonited barrels without issue. I hope that's the case...

Nitro-
Carburized or Melonite barrels have a very hard but thin
coating. The supplied cobalt drill bit should have no
trouble getting through.