Drill and tap K frame

[out of $]

Hello,
Recently I picked up a model 19-4 (4"). It is used with quite a bit of blue wear and some small spots of rust. By no means do I believe this revolver has any collectability. I picked it up to shoot 38 special target loads. My thoughts are to drill and tap the frame for a weaver base and add optics.
I am not up on specifics regarding drilling and tapping a K frame. My understanding is that the small 3-56 threaded hole, for the screw that holds the rear sight down will be very close to the front 6-48 hole that will be added for the base. What I believe is that on factory dilled and tapped models, first the 3-56 threaded hole is changed to 6-48, second is has been moved back(towards the rear of the gun). Becoming the front hole for the scope mount as well as the hold down for the rear sight.
Bottom line on a model not drilled and tapped, is there enough metal between the existing 3-56 tapped hole and the new 6-48 that will be added?
Or
Can the first two 6-48 holes be drilled and tapped and the third hole (in question) be left out.

 

[lscocoa]

I drilled and tapped my 17-3 a long time ago . Buy a weaver base for S&W revolvers first and take the sight off , you'll see none of the holes will interfer with the front sight hold down screw which you don't want to modify because you may want to re-install the sight some day .

 

[out of $]

What is the amount of material between the 3-56 hole and the 6-48 hole ?

 

[len917]

Hello,
Recently I picked up a model 19-4 (4"). It is used with quite a bit of blue wear and some small spots of rust. By no means do I believe this revolver has any collectability. I picked it up to shoot 38 special target loads. My thoughts are to drill and tap the frame for a weaver base and add optics.
I am not up on specifics regarding drilling and tapping a K frame. My understanding is that the small 3-56 threaded hole, for the screw that holds the rear sight down will be very close to the front 6-48 hole that will be added for the base. What I believe is that on factory dilled and tapped models, first the 3-56 threaded hole is changed to 6-48, second is has been moved back(towards the rear of the gun). Becoming the front hole for the scope mount as well as the hold down for the rear sight.
Bottom line on a model not drilled and tapped, is there enough metal between the existing 3-56 tapped hole and the new 6-48 that will be added?
Or
Can the first two 6-48 holes be drilled and tapped and the third hole (in question) be left out.

DON'T touch it. Buy a Weigand rail and have a gunsmith mount it.
jackweigand.com. I bought a rail for a K frame from Weigand and had local GS drill/tap/sight-in red dot, for less that $100.
There is a possibility of drilling thru into the cylinder and the screw may hit the cylinder and holes MUST be straight.
Best investment I made for my Model 15-3

 

[out of $]

Does the Weigand base have a different hole pattern than the Weaver base? If so does it move the front 6-48 screw hole away from the factory 3-56? My understanding is that the Weaver base uses the factory screw dimensions for a factory drilled and tapped model. I am aware that what I am asking about is other's solution/experance in drilling and tapping a model to the factory hole pattern.

 

[scooter123]

If you have access to a vertical milling machine such as the Bridgeport knee mill it's dead simple. If you are thinking about doing it yourself using a hand drill, DONT. These are very small tapped holes and you have to take care that you don't break off a drill or tap in the hole. If you do an EDM shop will charge you about 100 dollars per hole to remove those broken tools.

When I did mine I first drilled the holes undersized by 0.003 inch and then used a ream to get the pre thread hole exactly to size per the formula for determining tap drill sizes in the Machinery Handbook. I also put the mill in neutral and ran the tap into the hole using finger power and did a LOT of back and forth motion when tapping each hole. It took me about 2 hours to add the current hole pattern to my 67-1 and 617-0.

BTW, below is the standard mounting pattern used on S&W revolvers since about 1993. I'll also note that I intentionally shifted the pattern 0.03 inch to the rear to provide a smidge more spacing from the hole for the front sight mounting screw. BTW, after that 0.030 shift there is about 0.08-0.09 inch of web between these 2 holes.

BTW the black box in the Thumbnails area is a PDF format file so click on it, save it to your computer and print it out at your leisure. Note, this drawing was done by me and I grant any needing this drawing full access to use this file without concern about copyright issues.

 

[out of $]

Thanks for the reply! The diagram is great. I recently drilled and tapped a friends model 17. He had me not drill the front hole, as he felt in .22lr recoil was not an issue in using two holes.
The model 19 in .357/.38 recoil is an issue and I want the 3rd screw. Just where to put it is the question. I think you have a good idea shifting the hole away a slight amount.
Thanks
Tom

 

[len917]

Does the Weigand base have a different hole pattern than the Weaver base? If so does it move the front 6-48 screw hole away from the factory 3-56? My understanding is that the Weaver base uses the factory screw dimensions for a factory drilled and tapped model. I am aware that what I am asking about is other's solution/experance in drilling and tapping a model to the factory hole pattern.

I'm not really sure. Give Weigand a call, they are very helpful

 

[StakeOut]

I drilled and tapped a 625-2 myself on a milling machine and then installed a mount made by forum member revolver ph.On the mount I put a Burris FF3 3 MOA Red Dot.

I move the mount and red dot to other revolvers to test my reloads.I use just a dab of blue loctite on the screw threads

 

[riverman1]

Weigand even has a video, on the website, on how to drill and tap a revolver that did not come that way from the factory. Weigand is the way to go