Should you oil the outside of barrels that are finished in flat black?

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On Wednesday, February 13, 2019 at 5:48:16 PM UTC-8, unclevito wrote:
# Should you oil the outside of barrels that are finished in flat black?

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.
The minor diameter of #4 screws is 0.085", so they would work too.

But the coefficient of friction for lubricated steel on steel is 0.16
The static friction force threshold of slipping = [coefficient of friction lubricated steel][clamping force] = [.16][2873 pounds= 459 pounds.
Because the static friction 459 pounds is less than the recoil reaction on the scope mass 594 pounds, the scope should slip and the screws should start shaking loose.

Let us imagine a scope and rifle shooting well for years, and then caught in a rainstorm, it is later slathered with oil to prevent rust. Some of the oil creeps under the scope bases. Next year the rifle does not shoot so well.

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On 2/13/2019 5:48 PM, unclevito wrote:
# Should you oil the outside of barrels that are finished in flat black?

I have a Turkish SxS shotgun in flat black, and oil the barrels lightly,
then then wipe with a clean cloth to remove any extra.

I've never had a problem with it affecting the finish, or anything else.

For me, a lightly oiled barrel tends not to stain (from dirt, finger
prints, etc.) and cleans easier at the end of the day.

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On Sunday, April 28, 2019 at 9:14:33 AM UTC-4, clarkm...@gmail.com wrote:
Let us imagine a scope and rifle shooting well for years, and then caught in a rainstorm, it is later slathered with oil to prevent rust. Some of the oil creeps under the scope bases. Next year the rifle does not shoot so well.

Interesting analysis. I agree the screws should be loaded in tension, not shear. But where do you get your numbers for how much? The friction force available to resist movement will depend on how much tension is in those screws. Do you use a torque
wrench to install them?

My spring powered airguns have scopes that will routinely walk under the recoil (and will destroy a non-spring rated scope.) This is solved with a mechanical stop behind the base.

I think you're talking only about the bases walking, but a scope can walk inside the rings as well, right? And you can't tighten those too much without damaging the scope.

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On Sunday, April 28, 2019 at 6:14:33 AM UTC-7, clarkm...@gmail.com wrote:
# On Wednesday, February 13, 2019 at 5:48:16 PM UTC-8, unclevito wrote:
# # Should you oil the outside of barrels that are finished in flat black?
#
# 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.
# The minor diameter of #4 screws is 0.085", so they would work too.
#
# But the coefficient of friction for lubricated steel on steel is 0.16
# The static friction force threshold of slipping =
# [coefficient of friction lubricated steel][clamping force] = [.16][2873 pounds= 459 pounds.
# Because the static friction 459 pounds is less than the recoil reaction on the scope mass
# 594 pounds, the scope should slip and the screws should start shaking loose. #
# Let us imagine a scope and rifle shooting well for years, and then caught in a rainstorm, it
# is later slathered with oil to prevent rust. Some of the oil creeps under the scope bases. Next
# year the rifle does not shoot so well.

Oh, I doubt it? No shear? Are you kidding me? Shear is what IT IS ALL ABOUT?

When the rifle recoils, the scope screws are NOT in TENSION? THEY ARE IN SHEAR?

"Scope base screws are not stressed in shear, but in tension."

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On Monday, April 29, 2019 at 1:45:54 PM UTC-7, Peter Franks wrote:
# On 2/13/2019 5:48 PM, unclevito wrote:
# # Should you oil the outside of barrels that are finished in flat black?
#
# I have a Turkish SxS shotgun in flat black, and oil the barrels lightly,
# then then wipe with a clean cloth to remove any extra.
#
# I've never had a problem with it affecting the finish, or anything else.
#
# For me, a lightly oiled barrel tends not to stain (from dirt, finger
# prints, etc.) and cleans easier at the end of the day.

Of course! You should oil everthing on a firearm.

If the firearm is to be put away and not used for a while? I run a patch with 30 weight motor oil down the bore.

I put same on the outside.

Studies by American Gunsmith years ago found this to be as good as anything available --> at the time. <--

If the firearm is frequently used, some light, 3 in 1 or sewing machine oil is appropriate.

I've lately been using "EEZ-X" which is supposed to evaporate when put on lightly (it does) and leave a protective barrier behind (it SEEMS to.)

It seems to meet its promise but I have not been using it for that long.

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