doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com OT questions for the engineers.

I have been hunting with a crossbow and I like to use natural cover and hunt from the ground. I was sitting in my blind/hide tonight and took a few looks through my 4x scope and wondered if I would remember to pay attention to the ghost-like ironweeds and small branches that show in the scope view. I thought the 2.5X rifle scope I have would make those close-in extraneous objects more noticeable. My question: I've heard the reverse recoil of a crossbow can damage a rifle scope, but there has to be some forward recoil on a scope when firing a rifle or we would have to consciously move our shoulder back to where it was when we fired, right? Would that amount of force damage a scope, or am I thinking about it wrong?

We do move our shoulder and the gun back to the previous position for follow up shots. But that movement would hardly constitute a forward recoil inpulse that might damage a scope. It isn't the forward motion that causes the damage. It's the inertia generated by the abrupt stop of the internal scope erector mechanism.

Scopes for spring piston air rifles are designed to withstand the strong forward recoil impulse generated by the piston abruptly reaching the forward position. But even very expensive conventional rifle scopes may be damaged by them because they are only designed to handle a rearward recoil impulse. So if you are going to mount a scope on a crossbow, you may need to use a scope designed for that purpose. I am not a bowhunter, so can't say for certain.

“Forward recoil”.

The rifle goes back in recoil. The inertia of the scope makes it want to stay still.

This is what happens with a scope that slides in recoil in external mounts such as the 1907 vintage Winchester A5.

That was designed to slide in its mounts to avoid transmission of recoil stresses to the lens assemblies.



On a .303 rifle such as this 1910 Ross Mark III it goes forward about an inch and needs to be pulled back manually to the stop ring.

Crossbows generate more vibration than recoil, just as most pellet rifles do. It seems weird that a pellet rifle would cause a scope more problems than the recoil from rifle but it is a real fact. Most scopes, designed for rifles, will suffer long term use on any pellet rifle. I had a Leupold scope that had to be rebuilt after use on a pellet rifle. That rifle was a tack driver with the scope on it, but the vibration was so bad that the bottom leg of the cross hairs broke. Easy repair I am sure but it was not cheap as I paid for it instead of trying to claim a warranty covered repair. It was well known in pellet shooting circles that many scopes would not hold up long term and I took my chances and lost. Still that was a great shooting rifle and worth every dollar I spent on it. At 25 yards you could hit the primer hull end of a .410, every shot. At 50 yards you could put three shots into a dime. You could put your pellet into the eye of a squirrel and right into the brain with proper angle. Such a accurate gun is a true pleasure to own and shoot. That is one gun I regret selling.

Parabola, thank you. Your post reminded me of watching a bench rest shooter recently using a scope that worked the same. I remember him pulling it back. He also has a rest that moved with the recoil even though he was shooting a 22-rimfire.

Jon, thank you. Vibration certainly can create issues. A friend missed a deer on the opening day of PA's early muzzleloader season because the cap threaded on his inline had loosened and reduced the firing pin spring tension making a light primer strike.

I know inertia trigger double guns require firm pressure on the shoulder to exert the force that makes them function. The forces and vibrations must be much different than I imagine. I know I can definitely feel some recoil when firing my crossbow and high vibration has to be a factor. I am going to have to see if I can find schematics showing the difference in the build of airgun/crossbow scopes and rifle scopes just to educate myself. In an era of making things as inexpensively as can be done, I'm surprised scope companies haven't combined the manufacturing processes. I was considering a Weaver K2.5 which certainly is older tech.