6-48 or 8-40 screws on Leupold scope bases?

The screw size is dictated by the gun manufacturer. They are the ones who drilled the holes in the gun, the screws provided with the bases have to match. Most guns use 6-48 but there are exceptions.
 
When you buy Leupold bases for a certain gun, Leupold provides the correct screws. You did it correctly and the inch/lbs are correct.
 
6x48 is all I've ever seen on rifles, up to .300 WinMag, anyway. It might be that on "big thumpers", the mounting holes are drilled and tapped for 8x40, but I don't know.

I've preferred two-base scope mounts, since the bridge-type mounts have commonly used only three screws. More shear strength against recoil with four screws. For my hunting rifles, I figure than once I'm at one MOA or better, any alleged stiffening of the receiver is irrelevant. :)
 
The last leupold base I bought (1pc, picatinny base +15MOA) for a rem 700 had both sizes of screws included in the package, 6-48 & 8-40.

Edit- it says on the back of the Leupold package: 6-48=22in/lbs. 8-40=28in/lbs
 
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6-48 screws are the industry standard.
8-40 screws are found on Marlins and Henrys (perhaps a couple other brands).

Sierra280 listed (maximum) torque values.
 
The only place 8-40 screws/holes are commonly found, is on Marlin and Henry rifles.

Even most ring screws are 6-48. rather than the more fragile 8-40.

For most rifles, rings and bases will both use 6-48 screws.
 
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Even most ring screws are 6-48, rather than the more fragile 8-40.
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I was under the impression that 6-48 are the less 'fragile' screw...

I know I have read that some long range shooters will redrill and tap their stock 6-48 screw holes to 8-40 in order to 'stiffen' up their scope mount for consistency...

I was also under the impression that due to a greater contact of the threads, that they were less prone to loosening (without thread lockers)...
 
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They don't have greater contact. The difference is the overall diameter. The difference between the major and minor diameter is the same. Therefore, the "contact" surface is the same.
 
"Contact area" might be significant if you were to use the scope as a carrying handle. :) Diameter is significant for shear strength against recoil. Given the number of decades and the millions of rifles using 6-48 screws, there doesn't seem to be a problem.
 
Given the number of decades and the millions of rifles using 6-48 screws, there doesn't seem to be a problem.
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No one is saying there is a 'problem'...

My only point is that (it is my understanding) the 8-40 is not more "fragile" than the 6-48...

ADDING:

I apologize for screwing up my first post (pun intended)...

It has now been amended to correctly reflect my original intent that the 8-40 is not more fragile...
 
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My only point is that (it is my understanding) the 8-40 is not more "fragile" than the 6-48...
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It's not.
I don't know where that statement came from, or what I was thinking.
Perhaps I was hitting the cough syrup a little too hard yesterday.... :rolleyes:
Sorry for possibly causing confusion.


I think I'll edit the post; but leave the statement intact, so the subsequent posts don't seem like they're coming from left field.
 
Shear strength is a function of the cross-sectional area of the cylindrical part of the screws. The 8-40 would be stronger than a 6-48.
 
^^there it is. That's why leupold includes both with the rem 700 Mark 4 picatinny rail. While a factory 700 has 6-48 most (if not all) custom actions or builds are 8-40.
 
Thanks for the clarification...

I thought I was going loopy, and the number of times I had to edit my posts may well indicate that I am...
 
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