8-40 screws. Any gunsmiths in the house?

[SDHNTR]

I have a buddy who took his Wbee Vanguard/Howa into a smith with a supposedly good rep to have the receiver holes tapped out to 8-40 screws. He was gonna mount a big heavy Nightforce on it and wanted the bigger screws.

Job completed and when he went to mount his rail he couldn’t get the screws tight to secure the rail. Screws were standing proud. Even without the rail in place he couldn’t get the screws to go into the receiver more than 2-3 threads. As it turns out, the gunsmith didn’t drill and tap the holes through all the way. Now, I understand that on the front screw due to the barrel being under the receiver, but on the remaining 3 screws too? Why not drill/tap the back 3 all the way through and then grind the screws to fit if they protrude out the bottom, which I doubt they will.

When my buddy called the smith back and asked why he didn’t drill the back three screws all the way through he said he was uncomfortable with drilling them any deeper than he already had and just said to shorten the screws as is. He seemed miffed that someone would question his work. I don’t like his answer.

I don’t understand this logic either, but I’m no gunsmith. Every rifle I’ve got with 8-40 holes are drilled all the way through on the back three holes. Is there any reason not to? Wouldn’t you want as much thread purchase as possible?

 

[Rob5589]

Find a new gunsmith. Anyone that doesn't feel comfortable, yet goes at it anyway, is a hack.

 

[LRI_Chad]

I have a buddy who took his Wbee Vanguard/Howa into a smith with a supposedly good rep to have the receiver holes tapped out to 8-40 screws. He was gonna mount a big heavy Nightforce on it and wanted the bigger screws.

Job completed and when he went to mount his rail he couldn’t get the screws tight to secure the rail. Screws were standing proud. Even without the rail in place he couldn’t get the screws to go into the receiver more than 2-3 threads. As it turns out, the gunsmith didn’t drill and tap the holes through all the way. Now, I understand that on the front screw due to the barrel being under the receiver, but on the remaining 3 screws too? Why not drill/tap the back 3 all the way through and then grind the screws to fit if they protrude out the bottom, which I doubt they will.

When my buddy called the smith back and asked why he didn’t drill the back three screws all the way through he said he was uncomfortable with drilling them any deeper than he already had and just said to shorten the screws as is. He seemed miffed that someone would question his work. I don’t like his answer.

I don’t understand this logic either, but I’m no gunsmith. Every rifle I’ve got with 8-40 holes are drilled all the way through on the back three holes. Is there any reason not to? Wouldn’t you want as much thread purchase as possible?

Tapping a blind hole with an 8-40 tap sucks. It's why I gave up on it two decades ago and interpolate and thread mill the buggers in a CNC mill.

As for why he did this? It would seem he has his reasons. Whether it's viable is up for debate, as I've never been compelled to do it that way. It could be argued that leaving the ID receiver bore unmolested has advantages as a drill poking through almost always raises a cusp on the edge that the bolt body can hang up on. (again, why I interpolate the hole as this is avoided)

So long as you have around 1.5x diameter of thread engagement with the hole, you should be fine. An 8-40 screw OD is around .160" so if the holes are at least .240" deep of usable thread, I think you guys will be ok.

Good luck.

C.

 

[kswaterfowl]

Send your guns to @LRI_Chad from here on out. It will be done right.

 

[SDHNTR]

Find a new gunsmith. Anyone that doesn't feel comfortable, yet goes at it anyway, is a hack.

It wasn’t that he was uncomfortable doing the job to begin with, he said he was uncomfortabledrilling the holes any deeper, or all the way through.

 

[SDHNTR]

Tapping a blind hole with an 8-40 tap sucks. It's why I gave up on it two decades ago and interpolate and thread mill the buggers in a CNC mill.

As for why he did this? It would seem he has his reasons. Whether it's viable is up for debate, as I've never been compelled to do it that way. It could be argued that leaving the ID receiver bore unmolested has advantages as a drill poking through almost always raises a cusp on the edge that the bolt body can hang up on. (again, why I interpolate the hole as this is avoided)

So long as you have around 1.5x diameter of thread engagement with the hole, you should be fine. An 8-40 screw OD is around .160" so if the holes are at least .240" deep of usable thread, I think you guys will be ok.

Good luck.

C.

There’s nowhere near .24 inches depth. Thanks for that info though Chad.

 

[SDHNTR]

Send your guns to Chad from here on out. It will be done right.

I’m sure. But with such a simple job, I would have figured a local Gunsmith could’ve handled it. I’m wrong.

 

[kswaterfowl]

I’m sure. But with such a simple job, I would have figured a local Gunsmith could’ve handled it. I’m wrong.

I'm guilty of doing the same thing, and I learned my lesson as well. It sucks to pay shipping and is nerve racking trusting shipping companies with my guns, but everything I've sent to Chad has came back flawless.

 

[Wapiti1]

Couple of important points. You need 3 full threads on an 8-40 screw to get to full strength. This isn't based on a calculation, it's from old timer school. Lots of Mausers got 8-40 threads on the rear ring and it is only thick enough for about 3 threads if it's been ground to remove the charger hump. They hold just fine. 6-48 will get almost 5 threads.

He should have drilled through and fully threaded all holes possible.

In the end, if you really want to secure a scope, 8-40 is nice, but you really should pin the base instead. 6-48 with a 1/8" drill rod pin will never move. It's also way easier to pin a base in most cases.

Jeremy

 

[Mtnmilsurp]

What is this “pinning the base” that you speak of? Inquiring minds want to know. I want to know.

 

[SDHNTR]

What is this “pinning the base” that you speak of? Inquiring minds want to know. I want to know.

It's just an extra pin that fits into matching recessed holes in both the rail and receiver. Many custom actions come with them.

 

[BBob]

What is this “pinning the base” that you speak of? Inquiring minds want to know. I want to know.

 

[Mtnmilsurp]

It's just an extra pin that fits into matching recessed holes in both the rail and receiver. Many custom actions come with them.

Thanks! I told my wife this forum is educational…

 

[eLightfoot]

I never understood why use such tiny screws to attach rings/mounts to a receiver. Even 8’s are small. Why not a 10-32, then you could even get screws from a hw store in a pinch.

 

[2muchhp]

Drilling through would be standard procedure for sure and usually very doable. It hard knowing why he didn't do that. It sounds like he came up short on the tapping too, obviously because he was afraid of breaking the tap. I've had to use 4 taps on four holes for the very same reason. Maybe he was trying to use just one, not sure.
I do know that some receivers are harder than others and when tapping 8-40 into them by hand really puckers
a fella up