[quote=Clarkm]I have hundreds of rifles, like I am living in a gunsmith junk yard.
When I go to the range, I take tools and lots of rifles to test.
I help other people who are having trouble with bad groups.
For years I noticed that more than half my problems and other people's problems were the scope base screws were loose.
Then I did this simple derivation:
Scope base screws are not stressed in shear, but in tension.
If my 142 gr bullet maximum acceleration is from 500 fps to 2000 fps in 0.4 ms then an 8 pound rifle will try to accelerate from 1.27 fps to 5.07 fps in 0.4 ms. This is an acceleration of 9500 ft/sec squared.
If a 2 pound scope were part of that 8 pound rifle during that acceleration the force between the rifle and the scope would be
f = m a = 2 pounds 9500 f/ss = [9500 f/ss] [2 pounds / [Gc = 32 f/ss]]= 594 pounds.
If there were 4 screws in shear that would be 148 pounds force / screw.
That screw has a 0.12" minor diameter
A = pi r r = .011 sq in
Grade 5 bolt [American cap screws] has a shear strength of 72,000 psi
Each screw would have a shear strength of 814 pounds.
But they are not in shear.
They are in tension.
Grade 5 bolts are good for 127,000 psi in tension.
Each screw is good for 1436 pounds force in tension.
They are pre loaded to about half that, making a clamping force of 700 pounds.
The coefficient of static friction between the steel scope base and the receiver is ~ 0.6
So each screw provides a static state up to 420 pounds recoil force.
4 screws 1680 pounds.
But the hard kicking lightweight rifle and heavy scope only have 594 pounds peak force between them.
1680 pounds friction is greater than 420 pounds recoil, therefor the bases stay put.
If they were to slip, the screws might see shear forces, but that would require operator error in tightening the screws.
But you already noticed that 22 rimfires stay sighted in.
You can put all the oil you want on a 22.
Oil can cause wood stocks to split, but probably not with a 22.
[Clarkm I also try to help folks at the range. Loose mounting screws are the number one issue. Folks will shoot several boxes of ammo before asking for help. After may 10 instances this year alone the first thing I do is grab the scope and see if it moves. Many times it does. I had only one scope failure in may be 50 years until I started verifying zero from a good rest. One other thing I noticed is how few scopes actually are repeatable. I well remember with the old Weavers and Redfields if I ever got them zeroed not messing with the adjustments. I am still amazed at the number of "hunters" who refuse to shoot paper at least to verify their sights.
The only 2 Leupolds I have had that actually failed were a 2x7 after maybe 40 years on between a Number1 in 375 H&H and a Number1 in 300 win. and a new 1.5x5 after maybe 150 rounds on a .416 Rigby. All my fixed powers 2.5, 3, 4, and 6. Have been very reliable as have several 3x9's.
