Bear with me...
a 25 foot drop is a pretty traumatic event for any piece of gear. I think you need to separate the gun and the scope from each other to best isolate the problem. I think the rifle would tell you immediately if there was damage to such a degree that it would be off that much. You would likely feel wobbles or looseness. The barrel and action are married in such a manner, that the most likely problem would be where the receiver is connected to the stock- it's the weakest point. So check everything there and ensure it's all tight and there aren't any welds in the the barrel/receiver screw holes or inlets that have broken or loosened.
It's helpful when you're doing this, or when working on anything mechanical, if you repeatedly scream obscenities at the work piece. My go-to combo is usually, "You G*dd#mn F**in' C**k Su*kin' Murderin' Piece of Wh*re S#it!!!!" But everyone should tailor their work to their own individual personality.
I think, at the distances you're describing, parallax is not the issue. In fact, parallax doesn't really become all that noticeable until you're past about 250-300 yards and at higher magnification. The parallax error is miniscule. For example, a 4x hunting scope with a factory pre-set focus at 150 yards (the point at which is has zero parallax) has a maximum error of only 8/10ths of an inch at 500 yards. At the same magnification, at 100 yards, that maximum is about 1/5th of an inch. Remember, these are maximums. Your head would have to be really cattywampus to achieve the maximums.
If you've checked the mount, and found the rings and base are not wobbling, and everything is properly torqued - and yes, you can over-torque scope rings, which will cause tube compression and cause all kinds of tracking and zeroing issues - ( I suggest starting at about 25 in/lbs for the base and around 15 in/lbs for rings - some manufacturers recommend different settings)... then I think the scope's internals are the issue.
I'm assuming you haven't noticed any obvious damage to the scope - cracked lenses, bent tube, wonky adjustment knobs - then my assessment, with what you're describing, is that the erector assembly is damaged. I believe you stated (and my reading comprehension sucks - I've admitted that here before) that you bore-sighted, and found that the scope was tracking correctly. In my world, "Tracking" is when you place the cross hairs over a target at a given distance, dial in a change in windage or elevation, then return to the original setting and measuring the error, if any, in returning to zero. You would have to have the rifle mounted in a vise so it cannot move while you're fiddling with it and use a grid target that would allow to measure the error. This test is conducted for all 4 directions" up, down, left, right - and each measurement is the same - 25 clicks up, then back down, check for error; then 25 clicks down, then back up, check for error; and so on. You can also do a box test for tracking, which is, say, 25 clicks in all 4 directions in a row, and check how far off the hairs are upon return. That's, for example, 25 clicks up, 25 clicks right, 25 clicks down, then 25 clicks left, which should leave the cross hairs returned to the original position.
Other folk do a different "tracking" test whereby they set the cross hairs on target, then move the scope through the zoom levels and look for drift in the crosshairs as magnification changes. I'm guessing that you weren't messing with magnification changes while shooting, which would eliminate any contributions from magnification changes.
So here's my guess. I think the erector assembly was damaged in the drop. If the damage is only to a single part of the assembly - a spring or some such piece, you may not notice tracking error, because the assembly is not experiencing the stress of recoil. However, when you fire the weapon, the erector is now being traumatized by recoil, and being forced off zero. If that's the case, it's all over but the cussin'. You can either toss the scope or send it in for repairs.
Sorry for the long read. I hope it's helpful.
-Jim
