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Trivial recoil vs. scope question

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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/17/2008 at 20:23
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I recently came upon a local scope vendor who markets and advertizes the various brands of lowend scopes he sells being full auto rated for either .223 or .308. It just got me thinking how big a deal would a full auto firing  affect an average setup scope and mount. Example a low to midend spring airgun rated scope with a decent Bsquare weaver mount. Would the rapid firing, cycling action of a full auto assault rifle in say .308 be more harsh on a scope/mount than a bolt .308? I'm guessing yes it does but would really like to know from someone more experienced and with more  knowledge regarding the matter. Big%20Grin
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/17/2008 at 20:32
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Spring guns recoil in two directions. One from the spring moving to push the piston. The other from the large mass spring recoiling from the initial expansion. I have personally had bad problems from spring guns.
Though my 7.62 and 5.56 are semi-auto, the recoil forces are very similar to the full auto versions. My 7.62 is inertia operated (HK) and recoils fairly good for a black gun and has not damaged a scope, yet.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/17/2008 at 20:37
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One of the effect of scoping any Semi auto and more so on a full auto is the stress caused by the bolt slamming forward. It acts somewhat like the forward thrust of a spring airgun. With a bolt gun all you have is the recoil. all one direction. But with a auto there is bi-directional forces involved.

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/17/2008 at 20:38
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Tahqua you be fast.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/17/2008 at 21:14
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Originally posted by 3_tens 3_tens wrote:

One of the effect of scoping any Semi auto and more so on a full auto is the stress caused by the bolt slamming forward. It acts somewhat like the forward thrust of a spring airgun. With a bolt gun all you have is the recoil. all one direction. But with a auto there is bi-directional forces involved.



I think you are correct to a degree. But the foreward thrust on the springer is the initial expansion of the spring. A major part of the recoil is the recovery from expansion. This is where the problem arises.
If you look at initial recoil from a conventional firearm you will see that as the gun recoils, it wants to leave the scope behind, so to speak. That is why we seat all of our mounts against the front shoulders on mounts of this design. The gun moves back from oppositional recoil forces and the scope is up against the front of the cross slot, dovetail, etc. This is simple and in most designs is a three force member with a moment. But, I digress. A full auto weapon experiences the same thing only more rapid. The movement of the bolt forward is minimal compared to the initial rearward movement. The HK due to the camming of the recoil operated bolt is a bit stronger than a gas gun but the force vectors are the same.
A spring gun on the other hand has a large mass pushing the piston forward to compress the gas (air). The pellet leaves the barrel and the spring then rebounds from this compression. The initial compression recovery is what kills scopes and more importantly un-stopped mounts.
So, the initial force from the spring is forward. Once again it wants to leave the scope "behind". But in this case, behind is in your face. The ring is being seated against the front of the base like a centerfire.. When the spring recoils from this expansion the force is opposite and very rapid in duration. In this case the scope mount wants to seat against the back of the base. It is all very short in duration, too. I can assure you, owning a Webley Patriot, it is far worse than my .375 H&H from the optics and mounting point of view.
I am sorry to use some of the terminology but I hope I'm clear. Thanks, 3_tens.


Edited by tahqua - August/17/2008 at 22:36
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/17/2008 at 21:32
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I was going that for the fact that an auto will have two periods of thrust in opposite directions. Standard bolt gun only has one.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/17/2008 at 21:42
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Originally posted by 3_tens 3_tens wrote:

I was going that for the fact that an auto will have two periods of thrust in opposite directions. Standard bolt gun only has one.


All semi and full autos have that. The bolt velocity and resulting forces are generally controlled through regulated gas pressure or mechanical retardation via camming in the HK. This plus the recoil springs.
The spring in an airgun has high mass and the bi-directional forces in both directions are quite strong in the heavy ones. There is no control of the spring recoil force other than containment of direction within the tube.


Edited by tahqua - August/17/2008 at 22:00
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/17/2008 at 22:39
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A full auto and semi action has been said to absorb a little of that recoil so felt recoil is reduced. I find it somewhat true but haven't paid much attention to it. Wouldn't that translate to a less harsh battering on that scope and mount assuming you don't rapid fire it? I do agree though about hi powered springers being the most harsh on any scope except maybe them big african hunting rounds or the .50BMG.  Big%20Smile

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/17/2008 at 22:47
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some scopes are only designed to handle G forces in one direction. About twenty years ago putting a 2x scope on a 1911 was very popular, but the slide slamming was shut would rip up most of them. Leo did some changes, and alot of advertising and as a result their 2x pistol scopes have about the best resistents to forward inertial moments. in NFA weapons the gun can be still accelerating in the rearward direction when the next round goes of so the scenario is a bit different than air guns. the vibrations set up by the bolt slamming is still transmitted to the scope. current time lapse photos of scopes on fifties will actually show the scope tube flexing and an actual standing wave is produced in the tube as if it were a string or rope. generally ak47 type guns are worse than ar types because the mass of the bolt, carrier and operating rod is usually higher, -- I've torn up more scopes on NFA aks than ar for example, (conquest, diavari,even leo on 308s) NFA 308's are a little different because its so hard to hit anything with them anyway, anything other than short bursts are impossible. bushnells rather inexpensive air gun scope is an example of a scope designed as tahq has suggested. so no-- price is not a consideration. so the scopes you saw be NFA rated, but it still doesn't make them good scopes 
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/17/2008 at 23:15
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the recoil vector is transferred immediately to the bolt face and thru the gun, the only difference is the time factor, if the time can be spread over a longer period the recoil VELOCITY is lower, thus autos give an observed lower recoil, particularly gas operated shotguns. The momentum however is still seen by the scope as the same and its momentum of inertia is the same and the accelerating forces on it.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/18/2008 at 02:04
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Thanks sir DC. That's some usefull info i'd be passing around to my hunting buds here. Smile
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/18/2008 at 08:40
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 I recall a well-known gunsmith remarking that semi-auto shotguns were particularly hard on scopes, presumably for reasons already discussed here. It may have been Kenny Jarrett, but I'm not sure.
 I do remember him saying that Schmidt und Benders were his favorite brand for thier ability to hold up to it.
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