Can you guys recommend what type of bit to use to drill the pin holes and safety selector on a 7075 T6 aluminum LR.

I use uncoated hss drills 1/64" under sized then ream to size.

Are you using a mill or a drill and jig?

I use Cobalt HSS Parabolic drill bits for the job.
They are made to drill in "gummy" material like Aluminum.
I drill to size on my Taig CNC Mill.


The most important advice I can offer:
Drill before you mill the FCG pocket... Also Peck drill your holes!!!!!!!!

Peck drilling is where you drill for a short distance and fully retract the drill.
This clears the bit of any swarf, to insure a nice concentric hole. Also it allows you to apply lube!!
All of this makes a nice straight hole!!!

Good Luck,
Ca_Longshot

Precision holes are drilled undersized and reamed to final size.

The walls of a drilled hole are FAR from smooth.

Depends what you call smooth... that is a subjective term.

The +/- .0015 tolerance of the trigger/hammer pin holes may not be in the realm of standard drilled hole tolerance but any machinist worth his salt should be able to pick a bit, drill a test-hole and check, then hit the tolerance there-after. Sharp bit, test-hole that is verified in tolerance, then drill away.

Reamers are far more precise and much smoother than necessary for the pin-holes, but if you've got the right reamer and you want a higher precision level than necessary go for it!

The walls of a finished precision hole are NOT supposed to have the entire hole tolerance present in them.

Surface finish in a drilled hole from a twist but is NEVER as good as a reamed hole.

What hole in a gun have you ever seen that that was not shiny and polished smooth?

They are ALWAYS drilled under and reamed to final size.

Twist drills also routinely create a hole a few thousandths over nominal size and often tapered along the depth.

Reamers cut to exact size and leave a finished surface.

I use the bits that came with the 5D Tactical Jig. Work fine.

Holes from twist drills always have some surface roughness form the cutting edges of the drill bit.

It is simply an unavoidable property of the cutter.
The two cutting lips on a twist bit are never perfectly matched for more than a very short time on a brand new bit.

Twist drills also drill a lightly oversize hole compared to their nominal size.
Smaller bits can be way off if the bit flexes during the cut from cutting pressure.

I have never seen a hole in a commercially manufactured firearm that was sinply drilled.

They are far to 'clean' for that.
Drill it one size smaller and ream it to final dimensions.

HSS is all you need for any but the highest carbide containing aluminum.

These are not normally used in firearms since they are rather brittle.

We had some air frame pieces that had so much carbide content diamond tooling was used to grind though them.

A carbide cutter would not make it more than about 1/32 inch before cutting stopped.

Like I said, works fine. Not just for me but thousands and thousands of others who use a simple jig.

FFL Forum is here -> https://www.ar15.com/forums/Armory/FFL-Discussions/44/

If you want to discuss how an 07/02 does it. But it didn't seem he was one and was just doing a small number.

Use short stubby drill bits as regular drill bits are as stiff as taffy.

Use a center drill to spot the hole as a drill bit will wander a long way before digging into the aluminum.  Use lots of WD-40 as lube.

Only drill a very short bit before pulling out and cleaning chips.  Chips left in the hole will cause a drill to wander.

Drilling good accurate holes - before using a reamer - is harder than it looks.

Apparently there are a lot of folks that do not mind making poor quality guns.

Reamers are not exactly all that much money.

Do it fast and cheap or do it correctly.
You remain free to make the choice.

Sorry but you don't have a clue how guns are actually being made. I would bet a significant sum of money that most of the holes you think could have only been created with a reamer are actually nothing more than a drilled hole.

The GD&T on the print will tell you what the hole can and cannot have and I've NEVER seen GD&T on the pin holes that restricted the surface finish, cylindcricity, or circularity of those holes to a higher tolerance than the permitted hole size. You can make things up all day long and scream about them every day for weeks, it doesn't make them true.

Yes, yes, for deep drilling the holes can come out tapered, but we're not deep-drilling. Most quality drill-bits are tapered along their length to offset the hole taper issue. Sharpening those bits will create a smaller hole over time because as you get further back on the flutes the diameter decreases.

The hole finish necessary for pin holes is easily obtainable with a quality drill bit and a knowledgeable machinist. Can your garage tinkerer do it? Maybe, but he will likely have to work harder at it.

Maybe you're just projecting your terrible hole-drilling abilities onto others? I don't have any problems drilling good holes; I have to get my best bits out to do it, and I do it on my mill (not my cordless drill) but I can do it.

 Reading comprehension is key.  Yes, it is very easy to screw up a drilled hole.

I was not disputing that using a chucking reamer is the way to go after drilling undersize.  I was addressing something that was not discussed to this point.

Bundles of very good reamers are available on Ebay and dirt cheap.  Guys take care of them more so than other tools.

I have a box of perhaps 50 chucking reamers from ~.050 to 1" I use whenever the situation calls for them.