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The analogy of recoil on a rifle scope

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Brock_Brett View Drop Down
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    Posted: March/11/2009 at 09:51
The analogy of recoil on a rifle scope:

In testing recoil we are led to believe that scope’s lasting X amount recoil cycles greater than something that’s lasted Y recoil cycles is better.

In my findings and testing I have found that scopes tested in complete straight line recoil prove something but not everything. A scope is rarely subjected to pure straight line recoil. Most recoil is of many different axis.

1) Straight Line Recoil: The rifle recoils rearward and the scopes forces move forward on one straight axis. This is how most G load rigs test scopes (Drop Test)

2) Straight Line Recoil with muzzle lift: The rifle recoils rearward and the scopes forces move forward. Now with muzzle lift, the front bell is forced to flex down because of the upward lift of the muzzle. The same happens to the Ocular but to a much lesser degree.

3) Straight Line Recoil with side influence: The rifle recoils in a straight line and sideways such as the rifle sliding a bit sideways off the shoulder upon recoil. This coupled with muzzle lift has proven to be lethal on most all scopes. In most cases, this is probably the norm to some extent. In this case, the scope is moving in 3 axis simultaneously and, has recovery time after the recoil.

I’ve found in my testing that the faster the repetition, the more harm we’re doing to the scope. The only application I feel that can duplicate this is a semi-auto shooting 30-40 rounds rather quickly. In my simulations, I’ve found that 40 simulations at 1.75 second between simulations will cause enough heat in the main tube to be noticed by touch. Without nitrogen in the tube, the interior gas will start to purge past some seals at these temperatures. This is all accomplished by recoil in 3 axis, forward, sideways and down on all scope components. How well a scope can cope with harmonics will lend well to its longevity. In straight line recoil only, I have tested up to 600 simulations and felt no heat build up.

Overview: In my testing, I feel as though “how hard my rifle kicks” is a decent indicator of recoil but, feel the rifle weight and direction of recoil are the culprits of scope failures.

Rob
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koshkin View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote koshkin Quote  Post ReplyReply Direct Link To This Post Posted: March/11/2009 at 14:00
Very good observation.

ILya
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Post Options Post Options   Thanks (0) Thanks(0)   Quote pyro6999 Quote  Post ReplyReply Direct Link To This Post Posted: March/11/2009 at 14:02
i would also add that the velocity of the recoil is something to consider also, some stuff like the .30 cal wby's really have a swift kick speed wise, where as stuff like the 35 whelen is more like a push
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Ick Quote  Post ReplyReply Direct Link To This Post Posted: March/11/2009 at 14:58
Interesting, I hadn't really thought about heat in particular damaging a scope. Heck, I didn't even know to ask what kind of seal or gas is in my scope when I bought it.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote pyro6999 Quote  Post ReplyReply Direct Link To This Post Posted: March/11/2009 at 15:02
Originally posted by Ick Ick wrote:

Interesting, I hadn't really thought about heat in particular damaging a scope. Heck, I didn't even know to ask what kind of seal or gas is in my scope when I bought it.

obviously a lot of that will depend on whose scope you bought, some use argon/krypton/nitrogen etc. and the seals will obviously vary that much as well.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 3_tens Quote  Post ReplyReply Direct Link To This Post Posted: March/11/2009 at 19:57
The Krypton and Argon gas is heaver than Nitrogen. They would be less prone to leaking being a larger molecule.  Argon is 80% heaver than Nitrogen and Krypton is twice as heavy as Argon. Both would create a heaver surge because of the mass and motion of the recoil.

Edited by 3_tens - March/11/2009 at 19:58
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Post Options Post Options   Thanks (0) Thanks(0)   Quote trigger29 Quote  Post ReplyReply Direct Link To This Post Posted: March/11/2009 at 20:22
That's good research Brock. Thank you.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote koshkin Quote  Post ReplyReply Direct Link To This Post Posted: March/11/2009 at 20:22
Originally posted by 3_tens 3_tens wrote:

The Krypton and Argon gas is heaver than Nitrogen. They would be less prone to leaking being a larger molecule.  Argon is 80% heaver than Nitrogen and Krypton is twice as heavy as Argon. Both would create a heaver surge because of the mass and motion of the recoil.


Technically speaking, that is not correct.  Argon and Krypton, being noble gases, do not readily form diatomic molecules, while nitrogen's diatomic molecule is very stable (and is appreciably larger than Argon or Krypton atoms).

The only potential advantage for Ar/Kr mix I can think of is that when very hot, these atoms are marginally less mobile than the lighter N2 molecule.

In practical terms, I think the difference is largely important from marketing standpoint and not much else.

ILya
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Post Options Post Options   Thanks (0) Thanks(0)   Quote RifleDude Quote  Post ReplyReply Direct Link To This Post Posted: March/11/2009 at 20:24

That is a very interesting observation, B.B.!  Good post!

Ted


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Dogger Quote  Post ReplyReply Direct Link To This Post Posted: March/12/2009 at 07:25
You cannot get info like this anywhere else - thanks guys!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 308WIN Quote  Post ReplyReply Direct Link To This Post Posted: March/12/2009 at 08:01
GREAT INFO!Big Smile
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Brock_Brett Quote  Post ReplyReply Direct Link To This Post Posted: March/12/2009 at 10:42
Originally posted by koshkin koshkin wrote:

Originally posted by 3_tens 3_tens wrote:

The Krypton and Argon gas is heaver than Nitrogen. They would be less prone to leaking being a larger molecule.  Argon is 80% heaver than Nitrogen and Krypton is twice as heavy as Argon. Both would create a heaver surge because of the mass and motion of the recoil.


Technically speaking, that is not correct.  Argon and Krypton, being noble gases, do not readily form diatomic molecules, while nitrogen's diatomic molecule is very stable (and is appreciably larger than Argon or Krypton atoms).

The only potential advantage for Ar/Kr mix I can think of is that when very hot, these atoms are marginally less mobile than the lighter N2 molecule.

In practical terms, I think the difference is largely important from marketing standpoint and not much else.

ILya
 
 
Very well said ILya. I can see no advantage of Ar/Kr mix unless you get to some pretty elevated temeperatures.
 
But as mentioned, great marketing.
 
Rob
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 300S&W Quote  Post ReplyReply Direct Link To This Post Posted: March/12/2009 at 11:19
 GOOD read,as usual,Rob. Like Ick,I never really gave any thoughts to heat affecting a scope.  So I guess even with an external source of heat combined with certain types of recoil even if rapid shots aren't taken will take its toll on a scope?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Brock_Brett Quote  Post ReplyReply Direct Link To This Post Posted: March/12/2009 at 11:20
I've had a few questions asked on the affect of recoil and large bells. Much has to do with the plane in which recoil is transfered to the scope. In straight line, such as most all facilities test recoil it's not a large issue. Another issue that will help a large bell scope in recoil is the distance the bell is from the front ring. If the bell is close to the front ring the scope is less susceptible to see ill affects from recoil, this is recoil with other axis of influence.
 
Bottom Line: On a rifle that is of heavy recoil and is being shot from a bench, prone etc... There will be more tendency for failure on a large bell scope. Not because of it's size but, because of it's weight. Larger pieces of glass weigh more. Again the distance the bell protrudes beyond the front ring is another contributor.
 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Dogger Quote  Post ReplyReply Direct Link To This Post Posted: March/12/2009 at 11:30
Assume the issue here Brock is one of flex.  Any experience with the 25 Vs 30 tubes? Would think that it would not be difficult to increase wall thickness in a 25 to provide additional rigidity for heavy mag rifles as opposed to going to a 30mm tube
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Post Options Post Options   Thanks (0) Thanks(0)   Quote koshkin Quote  Post ReplyReply Direct Link To This Post Posted: March/12/2009 at 11:40
It is a design issue.  Generally, with the same wall thickness, 30mm tube is stiffer.  The question is whether scope makers who make large objective bell scopes take additional safety precautions to make up for heavier glass upfront.  I am sure some do and some do not.

There are also other ways to work around it.  For example, using more exotic glass (like in Zeiss Victory scopes) puts fewer lenses into the objective and the lenses are thinner and lighter.  That puts less stress onto the tube.

ILya
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 308WIN Quote  Post ReplyReply Direct Link To This Post Posted: March/12/2009 at 16:06
Originally posted by koshkin koshkin wrote:

It is a design issue.  Generally, with the same wall thickness, 30mm tube is stiffer.  The question is whether scope makers who make large objective bell scopes take additional safety precautions to make up for heavier glass upfront.  I am sure some do and some do not.

There are also other ways to work around it.  For example, using more exotic glass (like in Zeiss Victory scopes) puts fewer lenses into the objective and the lenses are thinner and lighter.  That puts less stress onto the tube.

ILya
I guess thats why the 30mm diavari with 42mm objective weighs 15oz and schmidt and benders 42mm 3-12 scope weighs 21oz!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote okc4956 Quote  Post ReplyReply Direct Link To This Post Posted: December/08/2009 at 06:37
Wonder how muzzle brakes fit into this equation of recoil forces. Heard brakes make scopes fail quicker? Any thoughts or data?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote cyborg Quote  Post ReplyReply Direct Link To This Post Posted: December/11/2009 at 13:24
Muzzle brakes relieve the amount of recoil. So if the affect on scopes is converse that would seem strange.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote koshkin Quote  Post ReplyReply Direct Link To This Post Posted: December/11/2009 at 13:31
Originally posted by cyborg cyborg wrote:

Muzzle brakes relieve the amount of recoil. So if the affect on scopes is converse that would seem strange.

That is true, but muzzle breaks seem to have a side effect of an odd vibration going through the rifle, plus the energy of the sound blast.  I think that makes the effect on scopes different than that of a rifle with strong kick, but no muzzlebreak.

ILya
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Post Options Post Options   Thanks (0) Thanks(0)   Quote cyborg Quote  Post ReplyReply Direct Link To This Post Posted: December/11/2009 at 13:35
AHA!!!!! Thanks Ilya.
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