Drilling and tapping a receiver

No, just standard carbide bits. Its amazing how much better they cut. Reading on AR15.com and some other more theory than practice sights on FSB drilling/reaming, these people are convinced 4150/4140 are some kind of ceramic undrillable anomaly. Carbide steel bits from a machine supply shop that cost $2.00 (Not a home depot!) and I can drill through the sight and barrel in about 15 seconds with a harbor freight drill press. A receiver is a much less stressing and difficult job for the tools,
Stay away from the gold junk and fake carbide from box stores, and shiny ones and steel is pretty workable.

What mjsd said, carbides work really good. Ive drilled a couple of old case hardened mausers with carbides after failing with standard bits. The standard bits wouldnt even scratch the surface, while the solid carbide bit ate through it like it was wood. I bought mine off amazon, I think they were about $6 a piece for #31 bits.

In the old days military rifle receivers were case hardened.
This gave a glass-hard thin surface with softer metal under it.
This produced a receiver that was soft enough not to shatter but with a very hard surface to prevent wear.

The problem was, the case hardened surface was as hard or harder then the available drills were so the receivers had to be altered to allow drilling.
One way was to grind off the case hardened layer in the area to be drilled, the other was spot annealing.
One method of spot annealing that prevented ruining a receiver from too much heat as when using a torch was the soldering iron method.

In this one an old fashioned large copper soldering iron was hung above the receiver with just the tip touching the point to be annealed.
The iron was heated red hot with an old gas blow torch and positioned with just the point on the spot. The heat from the large copper iron was transferred to the the spot on the receiver.
When the copper iron cooled to room temp, the spot was soft enough to drill and tap.

Today modern carbide drills eliminate all that.
All you have to do is be careful not to chip the drill and use a good cutting and threading fluid like "Do-Drill".
In order not to chip the drill bit it's best to use a drill press or milling machine.
Using a hand drill tends to allow movement that stresses the bit and it chips.

I had to drill into some serious hard steel a few years ago, so darn hard that carbide buts just skipped around. We had to resort to cobalt bits, and those darn things were not cheap.

Please pay attention to the advice given above and take your time, use a drill press, cutting oil (lots and lots of oil), use GOOD drill bits, and TAKE YOUR TIME.

Do you have a drilling jig with drill/tap bushings to position/guide the drill/tap?

Back in the day, when it was popular to accrue Model 98 Mauser actions for sporting conversions, I did quite a few VZ24 and Czech made Mauser actions for sporter
rifle builds. The rear of the receiver was ground using a mandrel between centers to emulate a Winchester Model 70 action, along with truing up the receiver bridge diameter.
When I first started doing this work I was still working as a cub, and apprentice toolmaker in a prototype department, so I did stuff after hours until I had made enough to buy my own machinery. I couldn't afford a Forstner drilling jig to do the Mauser & 03 Springfield receivers, so after hours I made my own copy of the Forstner fixture from steel end-stock in the scrap steel bin. Yes, I did install drill bushings of #31 size for the tap drills on an over-arm in my fixture, and my fixture has "V" blocks that are adjustable, up & down, and also in the "Y" axis on my mill.
I did find that some of the 03 Springfield actions needed to have the optics base screw holes annealed after they were drilled with a carbide #31, but I did that with a copper spud turned to size to fit into those #31 holes and then heated up with a propane torch until the area around the #31 hole turned red. Then I could cut the #6-48 threads with a normal #6-48 high speed steel tap.

I drilled and tapped a few large ring mausers, standard tool steel drill bits work just fine. I also drilled and tapped a few small ring mausers, they are case hardened, need to use a small grinding stone to break the case hardened surface, then tool steel drill bit works just fine. I never bother to use carbide drill bits, if too hard to drill, will be hard, or even impossible, to tap as well. I do have carbide drill bits, but never needed for drill-and-tap.

BBBBill said:

Do you have a drilling jig with drill/tap bushings to position/guide the drill/tap?

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In my case, I don't have one, borrowed from someone, worked great. Other times, I used Leupold style 1 piece scope rail, rubber band to the receiver, mount my scope and bore sight thru the barrel bore to position the scope rail, then super glue to the receiver. Remove the scope and the rail is my fixture for the center punch for drilling! Once holes are drilled, break loose the rail, clean up the super glue, and tap the holes. iI you bore sighted correctly, should be okay. I think I learned it from Steve Wagner's Turk Mauser page.

Back when I was a cub toolmaker I had some of the journeyman toolmakers help me do a "beefed up copy" of the Forstner drilling fixture that I couldn't afford on apprentice wages. This fixture puts the #31 hardened drill bushings "top-dead-center" over the bore, and action, center-line. The fixture looks pretty good and is super accurate with hole placement. Built like a Sherman tank. Hole tapping is done off the fixture and in a padded vice with a "V" block style bushing holder to guide the tap. I gave up on "carbon steel" taps a long time ago and have used nothing but "high-speed steel" ground taps for this type of work. One broken off carbon tap converted me without hesitation.
The bushing plate we made was for the same spacing that D/T holes are involved on the Winchester Model 70 rifles.
Once the set-up is verified on my milling machine. and the fixture lined up to the quill and bushings, hell, even a caveman can do it.

I have both the Forstner and the little B-Square drill fixture. You can do good work with both, but you can also screw up. No fault of the fixtures. Set a depth stop on the quill to avoid going too deep and check it ensure that it is locked in place. I have a really nice 96 Mauser receiver with a half hole all the way down the face of the upper locking lug seat. I don't really think it would hurt anything as it lines up with the ejector slot in the lug, but I replaced it with another one. I've thought of using it for a pistol caliber De Lisle type semi-clone, but other projects have taken precident.

Reading through this thread, I forgot to add in my post, as others have said, use cutting oil! You get a lot of heat drilling hard steel, and bits will get stuck and break without the oil.

BBBBill said:

I have both the Forstner and the little B-Square drill fixture. You can do good work with both, but you can also screw up. No fault of the fixtures. Set a depth stop on the quill to avoid going too deep and check it ensure that it is locked in place. I have a really nice 96 Mauser receiver with a half hole all the way down the face of the upper locking lug seat. I don't really think it would hurt anything as it lines up with the ejector slot in the lug, but I replaced it with another one. I've thought of using it for a pistol caliber De Lisle type semi-clone, but other projects have taken precident.

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I use a dial indicator for my mills "Z" axis and keep a sharp eye on that dial when drilling all blind holes, especially the two front holes on Ruger Mark I & II receivers not drilled from the factory. I use a dedicated drilling fixture just for those pistols hole locations.

I read each post and there is some mixed info along with the good. I am blessed with not only Gunsmithing skillset, but I’m also a Knifemaker & Machinist. A MUST with this is a firm background in Metallurgy. First thing...never, NEVER, ever try to soften a small area with heat! It won’t work.

Considering firearm parts which have a case or through hardening heat treatment ie., barrel, receiver, gas block, etc., we find hardness values in the 30-40HRC Rockwell. This is considerably lower than blade hardness knifemakers like me are familiar with.Typically high 50’s to low 60’s of the HRC Rockwell scale. Also some exotic steels mid to high 60’s HRC & one steel even registering 70HRC! Tungsten Carbide drills are harder than Cobalt, but also more expensive. That said, I generally buy Cobalt drill bits, M42 with 8% Cobalt, as they get through almost anything I need to drill and are much more easily sharpened. My end mills are almost all Carbide. No receiver made for any firearm is very difficult to drill. They are not hardened to even near Ceramic hardness! (Which is a general term anyway.... as there are many different ceramics with different hardness values.) In fact, a quality HSS bit freshly sharpened, will have little trouble with most tasks. The reason so many have problems, is because these people simply don’t understand what they are doing. Also, no matter the material, a dull bit, or incorrectly sharpened bit, can’t drill anything! This is the leading cause of the problems experienced. I’ve invested a great deal of time mastering drill bit sharpening. This is a freshly sharpened Cobalt bit I did with the one hand I have. My technique is flawless.

Learning to sharpen your drill bits pays big time! I have purchased bits that weren’t as sharp as they could be.

Lastly, as was mentioned, a drill press or Mill are IMHO, prerequisites for drilling these parts. I suppose maybe a hidden hole that only needs to be “Good enough for Government Work”, could be done with a hand drill. But drilling for anything which requires any level of precision, must be done with one of the aforementioned.

I drill & mill many different receivers and many, many hardened parts... I’ve never had any problems because I do so with the info I’ve outlined here.

I much prefer a "split-point" high speed steel drill bit for drilling most all receivers, titanium nitride coated, preferably. For blind holes I'll use a 135° split-point drill, and NO, they are not that much more expensive than carbon, or high speed steel drills with 118° included cutting angle cutting faces. I also have, and use #31, #33 & #28 carbide drills for holes to be tapped in hard steel, case hardened, or otherwise. As was posted above, Do-Drill is a great cutting oil to use for drilling receivers, chrome moly or stainless steel.
That hand sharpened drill bit pictured above has too thick of a web on its point for my taste and desired use. Smaller drills used for sight and optics bases, with a thick web cutting point like the one above, will have a tendency to "walk" on the work piece unless run through a drill bushing for guidance. I've seen that too many times when I worked as a toolmaker. We did a lot of Government procurement work, and the contracts never mentioned "good enough" was OK. It had to be, and better be to print!
So, I prefer a professional tool grinding service when my drills, taps and end-mills need to be resharpened. I find the end result to be much more precise, rather than having one flute cutting face any longer than the other and the drill cuts over-size. As always though, to each his own.

mjsdwash said:

Reading through this thread, I forgot to add in my post, as others have said, use cutting oil! You get a lot of heat drilling hard steel, and bits will get stuck and break without the oil.

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Quite often I'll use "spray coolant" when drilling through holes in a receiver, or even blind holes when the drilling is shallow.

I'll stick with what I was trained to do in my time working in a prototype toolroom for 16½ years. I was taught by indentured journeyman toolmakers, during my apprenticeship, from several European countries when Hitler chased those folks out of their homes. I don't need to prove anything to anybody, except my satisfied customers. I'll stick with the drilling procedures, and the professional advice, using high-speed steel, titanium nitride coated drills, of which I learned from the professionals I worked with, any day, every day, thank you.

SGW Gunsmith said:

Quite often I'll use "spray coolant" when drilling through holes in a receiver, or even blind holes when the drilling is shallow.

I'll stick with what I was trained to do in my time working in a prototype toolroom for 16½ years. I was taught by indentured journeyman toolmakers, during my apprenticeship, from several European countries when Hitler chased those folks out of their homes. I don't need to prove anything to anybody, except my satisfied customers. I'll stick with the drilling procedures, and the professional advice, using high-speed steel, titanium nitride coated drills, of which I learned from the professionals I worked with, any day, every day, thank you.

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sure, but I think I have burned more holed with Ti.ni. than I every cut!

mjsdwash said:

sure, but I think I have burned more holed with Ti.ni. than I every cut!

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Really? I try to get the "good" high speed steel drills, especially those smaller number drills like #28, #31 and #33, with the split point tips. They cut much freer with the off-set web and cutting tips, in my experience, with over 50 years of gun work. I watch those small drills carefully and can tell when they start to get dull, and then send them out for professional re-sharpening. Doesn't cost that much to get done and I know they will cut well.
I don't buy any of those inexpensive ChiCom or East India drills, because those are indeed crappy drills. Even the taps I use are tiN coated, and I find they do cut clean threads for a longer time than non-coated taps. So, no changes in the future for me, doing just fine, as is.

mjsdwash said:

No, just standard carbide bits. Its amazing how much better they cut. Reading on AR15.com and some other more theory than practice sights on FSB drilling/reaming, these people are convinced 4150/4140 are some kind of ceramic undrillable anomaly. Carbide steel bits from a machine supply shop that cost $2.00 (Not a home depot!) and I can drill through the sight and barrel in about 15 seconds with a harbor freight drill press. A receiver is a much less stressing and difficult job for the tools,
Stay away from the gold junk and fake carbide from box stores, and shiny ones and steel is pretty workable.

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Well, 4140 and 4150 is common barrel steel and machines very well, as I've found it. Drilling, tapping, turning, threading and cutting chambers is not hard on tooling as long as a proper coolant and/or cutting oil is used. Just because I prefer Do-Drill, because it can be included in my orders to Brownells for other things, is no indication, or should be falsely taken, that it's any better than any other "good" cutting oil. I never posted it is. It's no sweat off my two boys, if anyone prefers, and uses "bear fat", for that matter when drilling holes, or tapping.

I recently drilled and tapped a 1980s Miroku made 1895 receiver for a 'Climbin' Lyman' sight. Just used an electric drill, standard bits, and a little 3in 1oil. I think the key is a really good punch to get things started, but I am not an expert in metallurgy or the subject at hand.

SGW Gunsmith said:

Really? I try to get the "good" high speed steel drills, especially those smaller number drills like #28, #31 and #33, with the split point tips. They cut much freer with the off-set web and cutting tips, in my experience, with over 50 years of gun work. I watch those small drills carefully and can tell when they start to get dull, and then send them out for professional re-sharpening. Doesn't cost that much to get done and I know they will cut well.
I don't buy any of those inexpensive ChiCom or East India drills, because those are indeed crappy drills. Even the taps I use are tiN coated, and I find they do cut clean threads for a longer time than non-coated taps. So, no changes in the future for me, doing just fine, as is.

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yea, I'm sure the good ones are good. I was specifically talking about the cheap imports, the ones that are just a cheap electroplate of something gold colored. Because these are the majority of what people encounter, its fair to say stay away. As for cutting oil... I bought a bottle back in '07, and its leaked and gotten dirty enough I don't know what it is. I know it was pretty cheap. I have frequently drilled or tapped with only whatever oil I have on hand, just to keep the bits cool, and the chips moving. I wouldn't do that in a shop working with high end, or high volume, but it works fine for FSB's and pin holes. The joke about burning holes though, thats not entirely a joke. I used to get those cheap gold hardware store bits for installing cabinet pulls, and deadbolts. Drilling through those actually scored the wood pretty bad, and produced black smoke, and got very hot. I could have started a fire if I had some dry leaves on it.

I can’t say I’ve done thousands but the chamber reamers I have used we’re all HSS and the center drills I have used to begin with, when drilling and tapping were also HSS as were the taps. The drill are often not but not because HSS wouldn’t work but a cobalt bit will drill more holes before it needs to be sharpened.

I always use a milling machine, find center, then use the DRO to put the holes where they are supposed to go. Much less risk of breaking tiny things than positioning “by hand” methods.

mjsdwash said:

yea, I'm sure the good ones are good. I was specifically talking about the cheap imports, the ones that are just a cheap electroplate of something gold colored. Because these are the majority of what people encounter, its fair to say stay away. As for cutting oil... I bought a bottle back in '07, and its leaked and gotten dirty enough I don't know what it is. I know it was pretty cheap. I have frequently drilled or tapped with only whatever oil I have on hand, just to keep the bits cool, and the chips moving. I wouldn't do that in a shop working with high end, or high volume, but it works fine for FSB's and pin holes. The joke about burning holes though, thats not entirely a joke. I used to get those cheap gold hardware store bits for installing cabinet pulls, and deadbolts. Drilling through those actually scored the wood pretty bad, and produced black smoke, and got very hot. I could have started a fire if I had some dry leaves on it.

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Yes, I know exactly of what you write about. I got ahold of a few drills from India, but they didn't get used, they got thrown out after inspecting the cutting tip. Lesson learned.

jmorris said:

I can’t say I’ve done thousands but the chamber reamers I have used we’re all HSS and the center drills I have used to begin with, when drilling and tapping were also HSS as were the taps. The drill are often not but not because HSS wouldn’t work but a cobalt bit will drill more holes before it needs to be sharpened.

I always use a milling machine, find center, then use the DRO to put the holes where they are supposed to go. Much less risk of breaking tiny things than positioning “by hand” methods.

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Yes, I do also. I've skipped over the cobalt drill bits and endmills and have gone right to carbide for the tougher steels. Even some of those are tiN coated. The tiN is more of a coating that has a slick surface along the flutes to get chips out of the way of the cutting action along with a healthy flood of coolant.
I'll not be dissuaded from doing things the way I have been trained for, it's worked for over 50+ years, and that's more time than some have been on earth.