Gunsmithing Tapping stainless Ruger 77/44 for scope base - how damn hard is that action?

[Waorani]

Trying to put a picatinny base on a stainless Ruger 77/44. Tried the Weigand WEIG-A-TINNY but just don't like the way it mounts so ordered a Murphy Precision base. Very well made but requires drilling/tapping three 8-40 holes in receiver. I've opened up several R700 stainless & carbon receivers to 8-40 and never had any problems but this Ruger is giving me fits. Got the single front hole done without much issue but I've broken one tap (got it out) and can't get through on one rear hole and can barely even get the tap started on the other.

Anyone else ever try tapping a stainless Ruger 77 action? How dang hard are these things or did I work harden while drilling? Thought I was going slow and lubed starting with #38 and then 28. Also using quality 4-flute tap from McMaster Carr after my cheap Brownell's tap (that I've used for years) snapped.

 

[LRI]

"Tap" and "used for years" is a dangerous mix of words.

Most receivers end up between 42-46 Rockwell C scale when completed. Not soft, but not crazy hard either. That range of heat treat is where the toughness of the various materials typically likes to live. Stainless complicates things because of the nonferrous stuff present. Chromium, nickel, tantalum. None of these three lend themselves to "free-machining". Not all three are used in all types of SS. One has to know the exact composition to get a better feel for it. Sulfur is often added to improve machinability but again, it all depends on what is being used. The only way to know is to have a formal analysis done. Not expensive at all. A hardness test should also go along with this.

Adding to the complexity here, it is very possible that the receivers are induction hardened at the lug and rear bridge features since that's really the only place they need to be. From a cost perspective, it doesn't get any easier than this. Stick the part in the "death coil", apply a magnetic field that generates a ton of resistance, part glows, toss it in oil, water, a high flow of air, whatever. It's a very simple thing to do. It also makes for a tough piece of steel that eats taps.

I realize I'm a bit spoiled but there's a good reason why I gave up on tapped holes in actions a long time ago. Milling the threads offers a far more predictable outcome. If you get stuck, I can help and would be happy to do so.

C.

 

[Waorani]

"Tap" and "used for years" is a dangerous mix of words.

Most receivers end up between 42-46 Rockwell C scale when completed. Not soft, but not crazy hard either. That range of heat treat is where the toughness of the various materials typically likes to live. Stainless complicates things because of the nonferrous stuff present. Chromium, nickel, tantalum. None of these three lend themselves to "free-machining". Not all three are used in all types of SS. One has to know the exact composition to get a better feel for it. Sulfur is often added to improve machinability but again, it all depends on what is being used. The only way to know is to have a formal analysis done. Not expensive at all. A hardness test should also go along with this.

Adding to the complexity here, it is very possible that the receivers are induction hardened at the lug and rear bridge features since that's really the only place they need to be. From a cost perspective, it doesn't get any easier than this. Stick the part in the "death coil", apply a magnetic field that generates a ton of resistance, part glows, toss it in oil, water, a high flow of air, whatever. It's a very simple thing to do. It also makes for a tough piece of steel that eats taps.

I realize I'm a bit spoiled but there's a good reason why I gave up on tapped holes in actions a long time ago. Milling the threads offers a far more predictable outcome. If you get stuck, I can help and would be happy to do so.

C.

Thanks Chad, was hoping you'd see/respond to this. Probably should have sent to you to begin with but seemed like a simple enough project given past successes and not worth pestering you. I thought about induction hardening at the rear bridge and you're probably right. I'll call the shop tomorrow to see about getting it in to you. Multiple repeat customer but my first need for goobersmithing fix.

 

[lariat]

Thread milling is the way to go, hands down. You can control the major and minor much better with a drill selection and thread mill than with a drill and tap. And if it breaks you can remove the end in the hole, put in a new thread mill, reset the tool offset and go at it again with minimal issue. Dull taps are the worst in steel. Its a tool that lies to you about how willing it is to do the job and refuses to leave once its there.

 

[Waorani]

Agree but beyond most home shops. I was using the Bridgeport for drilling and tap alignment though.

 

[lariat]

Don’t get me wrong I’m not running you down. Stainless and taps are difficult, at least it has been for me every time I have tried it. Never could get it to work consistently in small threads. I felt like I found enlightenment when I got exposed to thread mills.

Every red blooded American needs a Bridgeport.

 

[LRI]

I think a big part of this problem is that there is a monumental vacuum when it comes to high quality tooling for gunsmithing.

The 8-40 tap in particular. I am not aware of a single mainstream tooling vendor that makes these. Emuge is who I use whenever possible as the performance they offer is absolutely sterling and they have very application-specific tools designed for the more obnoxious materials. I wish they would jump on this fertile soil. I'd buy the shit out of em just because it's nice to chase a hole that might squeak a smidge after a treadmill wears a bit.

 

[FisherT&C]

Rugers are cast so they are hardened all the way through and very tough. I drilled and tapped a Swiss K31 years ago and several 1903s which are really hard as well. I would bump up to 10-32 screws and use a carbide drill bit. A beefier tap is less likely to break. That's what was recommended by the manufacturer of the K31 scope base and it worked.

 

[clcustom1911]

Don’t get me wrong I’m not running you down. Stainless and taps are difficult, at least it has been for me every time I have tried it. Never could get it to work consistently in small threads. I felt like I found enlightenment when I got exposed to thread mills.

Every red blooded American needs a Tree 2-UVR

Fixed it for you

 

[Waorani]

Thanks Chad @LongRifles Inc. for fixing my boogered attempt at drilling/tapping this M77/44 for scope base screws. I know it had to be more trouble than it was worth!