Tapping Stainless Steel???

[Skeezix]

Am installing a trigger overtravel stop screw in the trigger housing of a Ruger 77 Mk II Stainless rifle (#6-32 set screw). Have successfully drilled the hole through the front of the housing, but due to the thickness of the steel, couldn't keep the steel cool enough to keep it from hardening even though I used Mistic Metal Mover as lube while drilling at 990rpm on drill press.

Have started tapping the hole for the 6-32 set screw.  Can't get it threaded past about half way due to the hardened steel.  Have ordered a Cobalt Vanadium Steel spiral point tap with oxide over nitride coating that is supposed to be able to tap stainless.   But I don't know if it can handle hardened stainless. 

Do you think this fancy new tap will work?  Or am I going to have to go with carbide (expensive!!)?  Or try something else?

I've thought about trying to drill the hole out another 0.003" to make it easier on the tap, but I don't know it I could get it to drill oversized without breaking the bit.  I've got some fancy powdered metal steel technology, 130 degree split point bits with TiN/TiAlN coatings that are supposed to be the cat's meow for drilling stainless.

[gunnut69]

I tried the same thing and could not get a hole tapped with carbon steel so just installed a riveted in place stop and adjusted that with a file. A little simple but it is hard to jack up once installed.. I found that the steel had inclusions and whatever they were they were harder than h**l. I assumed they were probably chips of ceramic material from the investment cast process.. Let us know how it works out. The hausing I was working with had a dimple where I needed to install the screw. It seemed as if Ruger intended to put one there at initial design time but backed out before starting production. I have been sorely dissapointed with Rugers quality in the MK II action. The safety in particular seemed a aloppy fit and a bit crude.. I MUCH prefer the original M77 action,..

[Skeezix]

gunnut 69, I was able to drill the hole just fine, but there wasn't a dimple there already.  I had to centerpunch the heck out of it.  Could have used a center drill also.  Anyway, am waiting on the fancy drills and taps from McMaster-Carr.  I may end up having to drill the hole out oversized to add a little clearance around the minor thread diameter and ease the tapping process.  I've got another M77 Mk II that I haven't modified yet, that's blued steel and I'll check it to see if there's a dimple there.

The safety worked really rough and you couldn't feel the detents on the three positions, but I tore it down and the dang thing was FULL of machining debris from the manufacturing processes. I cleaned it up good and lubed with some good synthetic grease made for stainless and it's as smooth and positive as any Model 70 Win safety now.  Once you go through them and clean them up good and do a little polishing here and there, I really like the Mk II actions.  Once you do that, I believe the innate quality and ruggedness is better than any of the Model 70 Winchesters built in the last 15 years or so, IMHO.

[gunnut69]

The safeties I've worked on (just a few) also were full of crud but I seem to remember it as being grit..perhaps ceramic debris. Also the M70 safety is more positive, as it actually locks the striker, not just blocks the trigger. I much prefer the original M77 and it's thumb safety. It's in a very conmvenient place and is positive in function (also just a trigger block). The original M70 trigger is a very good design, simple and rugged and the safety is completely positive. The last iteration of the M70 'claw' guns had some QC problems for certain sure. I just believe the M77 MK II could have been so much better and should have been.. I've a M77 7mmRemMag and it's a great rifle,(stocks a little plain) but I've never seen a MKII that I'd trade for.. Seems the Remingtons are headed down a similar path as I've seen several that were not functional as received from the factory. The first few years the 870 Express guns were out a local shop was forced to return more than 1/2 they received. I've even had to worki on a couple of Ruger 22 auto pistols..both military grip models.. Sporadic jams and eratic function failures, the cause? Bits and pieces of plastic detritis inside the frame cavities that ocasionally worked it's way into the action. I cleaned the guns, shook out the plastic bits and reassembled..all functioned fine. I've even been haering bad things about the marling QC of late (since it's purchase by Remington). I've a lot of M700's, M7's etc. and am saddened by the slop they are turning out now..

[Skeezix]

SUCCESS!!!  Got my fancy tap today from McMaster-Carr and it worked like a champ.  Gently turned it into new metal about 1/10 turn at a time and then backed it out a little more than that to clear the chips.  Slow and easy got the job done.  Have installed the overtravel stop and with the other tuning of the trigger I did, it works slicker'n snot on a glass doorknob. 

gunnut69:  The Ruger 77 mk II safety IS positive and DOES block the striker in the rear position, same as a Win 70.  Check the pics below:

The first pic is the Ruger 77 Mk II safety in the middle position, which blocks the trigger only, and allows opening the action to unload or load cartridges. 


Here is a pic of the safety fully in the rear position.  Note that the safety lever engages a slot cut into the rear of the striker, thereby fully locking it and preventing it from falling.

[D Humbarger]

In the future use Tapmagic.  The best cutting fluid for stainless steels on the face of the earth.

[BW56]

Nice job. You got it right, slow and clear a bunch. tap magic would have helped.  I was always told a 6-32 was the weakest tap ever. I prefer a 0-80 or 4-40 over a 6-32 any day.

[gunnut69]

Skeezix- I don't remember that striker locking feature on those I worked on but it's likely CRS... The older I get the worse it seems... The M77 has some great features and all rifles should use the built in bases for scope rings used on the M77. They NEVER work loose! What caliber and how does it shoot?

[Skeezix]

BW56 & D Humbarger:  Tap Magic WAS used through the entire tapping process.  Have been using that stuff since the 1970's, back when it had its original formulation which was much better than the present "environmentally friendly" formula.

Note the can lurking in the left background of this pic:



gunnut69:  The caliber is .270 Win, and I haven't shot it yet.  The rifle is six years old, but never been fired, yet.  Mounting a Nikon Buckmasters 3-9x40 scope on it to start with.