I recently built my very first AR15, and I attempted to dimple the barrel for the gas block, but the drill bits I was using were only hard enough to leave a cosmetic mark on the barrel and not actually drill into the metal. As a result I just gave up doing that and fastened the gas block with block Loctite. I've decided that I would like to have another try at dimpling the barrel, because I'd rather not have this rifle be damaged in the gas that the gas block would rotate. What are the proper drill bits to use for this?

It more than likely won't rotate, it's more of maybe causing a pinch point to mess with accuracy. If you're using a hand drill it's going to take some work, no matter the bit, a drill press is better (not a must though). Just use quality bits not the Harbor Freight ones, you could always pull the barrel and have a machine shop do it, around me it'd probably be about $20 if you pay cash.

Check over at SLR Rifleworks website. They sell a dimpling jig and a drill bit. There's a video linked there on exactly how to do this.

Carbide Counter Sink

or

Carbide Short Length Drill Bit

I just used standard DeWalt drill bits from Home Depot, like these:

Drill bits

Could also be OP that your drill bits are decent quality but just worn out.

Center punch and try with a new bit. 

I used a cordless drill so there's no reason you shouldn't be able to do the same. 

WHAT is the barrel made of ??

How fast are the drill's rpm's ??

You do know that some metals are harder on tooling....like stainless steel for example.

So if you wanna play gunsmith, maybe invest in some decent tooling and educate yourself to the proper techniques required to do the job right.


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Geissele recommended for gas blocks

I would hardly call drilling a couple of dimples for a gas block, wanting to "Play" gunsmith.

They recommend Cobalt drill bits but they don't do so well on Nitride barrels with a hand drill.  You need to be patient when dimpling nitride barrels.  Keep the bit wet and take your time.  Do not use a lot of force, use slight pressure and let the bit do its job or it will get dull very quickly and be useless.  I was dimpling a few barrels last night.  One was a BA stainless barrel and the other two were a BA and Faxon nitride barrel.  The stainless barrel was very easy to dimple and the other two seemed like it took forever to just scratch the surface.  I have had people recommend solid carbide bits but they are $22 a pc and usually need to be ordered or bought from a specialty parts shop like a Fastenal or Grainger.

Carbide drills will cut melonite no problem.

disregard 

Sharpen your drill bits first.  Check a machinist handbook to figure out how fast it should be turning and comply.  Use lubrication.  

If your current bits won't hold an edge, then step up to some nicer coated bits.  However, I don't think they'll be absolutely necessary.  But they would be very beneficial if you're planning to do a handful of these.  

I've sharpened bits by hand for years.  You don't need one of those fancy drill bit sharpeners if you take your time and pay attention to detail.  I prefer to do them on a bench grinder, but have sharpened them with belt and disc sanders more than a few times.  Get on the google and figure out your angles.  It will take some practice to get it right.