POI Shift wanneer geweer val
Posted: Mon Jul 29, 2019 9:51 am
Ek het die interressante stukkie raakgelees op FB. Ek gaan van nou af sommer al my monterings se skroewe lube wanneer ek hul opsit.
A very good post by Hakan Sphur on another group
A few years ago after reports of POI shift on a gun after it fell over while resting on its bipod I did a lot of testing to determine the cause of this and how to resolve it.
I did both tests on the range and in the workshop, where I would smack the scope with an open hand - roughly the amount of force you would use to start a bar fight. Most of my testing was done in a milling machine where I mounted two vices, one with a collimator and one with a heavy duty picatinny rail.
I tested a lot of mounts, or more or less all the important mounts on the market at the time and the results were pretty clear:
If the surface betwen the picatinny rail is dry when the mount or rings are installed, the best mounts and rings would have 0.4-0.5 mil shift in the direction of the smack. The worse mounts and rings had 2-3 mils total shift.
Everything was checked with a dial indicator to see where the movement was occurring. And the movement was betwen the mount and the rail.
When lubricant was added, the better mounts and rings in the test such as ours and Badger USMC rings had less than 0.1 mil movement.
Why?
Its rather simple. If a screw is torqued dry about 95% of the torque is lost in friction. If lubed the result is way better, but still the majority is lost in friction.
So a dry mount against dry rail means that the mount hangs on friction. When a scope or a gun takes a hit, the mount can shift, but with a quality mount and a lubed rail the issue disappears.
Loctite:
I haven’t tried to loctite betwen picrail and mount, but i have tried to loctite betwen TRG rail and mount and that gave less good results than oil!
I encourage everyone to zero your gun and start smacking your scopes, and don’t forget to post the results here!