I'm wanting to purchase some taps and required drills and wanted to know what sizes are most used in your gunsmithing endeavors, in general and scope/peep sight mounting in particular. I have access to a quality mill so no worries there.

Thanks for looking.

I get by with a couple good small center drills, a couple good hard spotting drills...for number 4 screws a 33,43,42 for number 6 screws a 28, 36, 31 for number 8 screws a 19, 29, 28. That will 90% cover what you will need. Bigger sizes for guard screws, I buy as needed. One thing I like is a 3 flute hard drill in #33 for old milsurp receivers. IMO 2 flute taps are worth the money, I have never broken one (shouldn't have said that out loud).

I bought a complete drill index all the way to 1/2" from about 1/16" .Then bought drills, starter tap, regular tap, bottom tap kits from Brownells.4-40, 6-32, 6-48, 8-24, 8-32, etc.

Definitely center drills (buy several of each size).

Drill index set has bits that are possibly close, but not the recommended bit for the common gun screws.

All the proper required size bits are Number drills.

Ya might find some receivers that are kind of impervious to the steel twist bits.

Brownells has some kits you should look at.

Over time when you have actions in the shop It’s also a good thing to get the taps and dies for action screws because people doing self bedding jobs can get bedding material stuck to them and you need to clean them off / out by running a tap / die down them.

Get a good thread gauge so you can see if a screw is a 6-40 or 6-48... as well.

It’s fun when you have to buy both a bottom tap, and regular tap for most of your common work (scope base screws that Saddlesore mentioned).

You can buy drill indexes with both size fraction and decimal and number drills.I have one.

Here's your drill set https://www.mscdirect.com/product/details/73285355 Don't even think of getting the chinese junk as you'll regret it. They also have allot of better and less expensive taps than Brownells.

Yes.That is the one I bought.

I mentioned the Brownells one as they do have kits.I am sure there are several places that sell better tooling .We have a small shop here in Colorado Springs. " Shop Tools " thatis oneof them

Why spend $300. on sets of drills many of which you'll never use ? Buy packages of screw machine length drills in the tap drill sizes needed. As for taps Reiff & Nestor brand are the best there are, R & N has been in the business since 1908 their quality control is the best in the industry. They control the tap geometry more tightly than other manufacturers, as a result less torque is necessary resulting in a tap that is easier to use and breakage is significantly reduced. Plug taps and bottoming taps are the ones that you'll use in drilling & tapping for scope mounts and other gunsmithing work. Good quality tapping fluid is a necessity to produce quality threads, in tougher materials you can go a few thousandths bigger than specified tap drill size. Tapping effort is reduced resulting in less breakage and the threads are still plenty strong enough. Taps most frequently used in scope mounting are #6-48 and #8-40, #3-56 is the size for shotgun beads. Hope this info is useful, lastly I buy my drills & taps from MSC and McMaster-Carr. They have everything you need and delivery is the best in the industry.

[quote=gunswizard]Why spend $300. on sets of drills many of which you'll never use ?

Because many of us use drills for more than sight/scope gun work.I have probably used more than 80% of the drills in my index.I even have 9/16. 5/8 ,3/4 and 13/16 drill bits.Long drills and short stubby drills. Sometimes you have to start smaller and work up incrementally. Like when drilling up thru a stock from the butt for some shotguns.I also have some adjustable reamers that I pre drill a hole and then custom make sizers for over sized cast bullets or and expander plugs. I had to make a hole for a muzzle loader ramrod and after using a long drill, I opened it up with a piece of 3/8 ths threaded rod.
I prefer to have something I might not need than not have it and need it

Brownells and Midway USA for taps. I get carbide drill bits when I can. I have gotten some taps with the associated drill bits from Menards. I don't have the number or letter index drill bits but I wish I did.

Every fall Midway USA remembers my birthday and I stock up on taps, dies and drill bits for a good discount.

kwg

I always ordered just the ones I commonly used, had a couple cheaper drill indexes for the ones that saw rare or occasional use. If ordering from Brownells I had better luck with the USA made taps over the house brand stuff. Ultimately I ended up getting a better deal on better tools through MSC.

I always carried a tube from a 3/8” endmill in my apron. Inside was a #31 stubby drill, a #28 stubby drill, a matched set to go with the aforementioned but with their points ground off to make flat bottomed holes for getting the maximum number of threads when installing sights on barrels, 6-48 and 8-40 bottom taps with %90 of the taper ground off the ends, a #0 center drill, and a 4 flute 1/8” center cutting endmill. This tiny kit takes care of %95 percent of drilling and tapping operations pertaining to sight and scope base installation. If you’re using a milling machine like I was the endmill can be used carefully to plunge cut out the center of a broken tap without ruining the hole.

I’m partial to Tap Magic tapping fluid for drilling as well as tapping. Pro tip of the day is that if your tap gets dull get rid of it. You may not be able to see any damage but it will start to stick and squeal and not cut smoothly. Back out while you’re able and get a new tap, they’re a lot cheaper than the effort and time it will take to fix whatever happens when you snap one off in a blind hole.

Do some research on drill alloy. IIRC cobalt alloy drills are best for drilling scope base holes.

I'd also recommend a drill point gauge and a quality grinder. Learning to sharpen a drill bit will be money in the bank. I can sharpen one in the field with a cutting wheel or in the shop on a bench grinder.....although my Oliver Adrian bit sharpener does better than I can.

If you click on the resources tab it'll share some good information.

https://www.oliverinstrument.com/pdfs.html