Follow along with the video below to see how to install our site as a web app on your home screen.
Note: This feature may not be available in some browsers.
What is " 1.5X the root of thread engagement" expressed in?a) The screws will fail in tension if torqed too hard if there is MORE than ~1.5x the root of thread engagement.
b) The female threads will strip out if torqed too hard if there is LESS ~1.5x the root of thread engagement.
expressed in a ratio.What is " 1.5X the root of thread engagement" expressed in?
This might hold true for a rail with a recoil lug or pin, but not for those without. Once the friction from the normal clamping force is overcome, those screws WILL be in shear and bending and tension during a shot. Which load causes them to fail? All of them. You can't put a blanket statement on the levels as scope, scope rail, ring, action surface finish, rail bedding, rail surface finish, screw clamp load, gun weight, cartridge, gun CG all come into play.A lot of guys think the stress on scope base screws is in shear. The screws are clamping with tension. The shear forces are between the scope base and the receiver.
Some things to keep in mind:
1) a) The screws will fail in tension if torqed too hard if there is MORE than ~1.5x the root of thread engagement.
b) The female threads will strip out if torqed too hard if there is LESS ~1.5x the root of thread engagement.
2) Max torque ratings for screws may be for #5 grade, but that chart should be tempered with:
a) 100 % for dry threads
b) 75% for oiled or greased threads
c) 50% for waxed threads.
3) A scope may stay sighted in for years until oil gets under the scope base.
The coefficients of friction for scope base to to receiver connection:
Clean and dry: 0.76 - 0.80
Lubricated: 0.16
If there is 400 pounds of clamping force and 4 [6-48] screws, the 1600 pounds of clamping force can withstand 1200 pounds of recoil force on the scope with dry base to receiver connection. But if oil creeps under the base, only 250 pounds of recoil force on the scope mass will be resisted.
Using Quickload:
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 recoil force on scope.