I have an LMT AR with a nightforce optic, I will be getting an another AR which will most of the time will have a red dot. However on some occasions, my plan is to swap out the nightforce optic and put it on my second AR. Would the continued taking off and replacing the night force optic damage the LMT pic rails over time?
The night force optic is on a night force XTRM - Unimount
So you plan to swap out optics between two AR’s over and over again? I guess I would question as to why you would do that? With that everything will wear with use, but I doubt you will do any significant damage/wear mounting and unmounting optics on occasion.
You will have different barrels so your dope for each will be unique for each.
So, you need to grind out the numbers for each barrel with that scope…and reconfirm when replacing the scope…each time.
for me…the juice isn’t worth the squeze.
YMMV
No. You won’t damage the rail if you’re not doing anything ridiculous. The finish wear may accelerate, but If it were me, I wouldn’t care about that.
If I were going back and forth, I’d prefer to leave it on one gun for a while due to the reasons mentioned above.
Why would you do that? What’s the purpose?
Perhaps you do that a couple of times to decide which of the two ARs is better suited for long range shooting and which one is for shorter ranges and home defense. But at some point, you would set them up for a specific purpose.
There was an instructor, maybe with Magpul’s training thing they had going. Todd something?.. a real good long range shooting instructor. He made the point that if you had limited funds for Glass, it was better to move 1 good scope, than say 2 Vortex scopes for example.
I do that quite often. Why? I have other bills to pay, and I still owe people money. 
Wear and tear are there but minimal. There are a few practical issues to overcome.
I use scopes with exposed turrets exclusively for this purpose. I zero the turrets for one rifle and will keep the zeroing unchanged ever, even when the scope is moved to other rifles. I have a new dope table printed out and taped to backside of the eyepiece cap. That table is based on the indicated w/e figures of the scope. It may look like this
W +3
100yd 4.00
200yd 6.25
300yd 9.50
…
For the new rifle, windage set to +3 moa for no wind. Elevation set to +4 moa for 100yd etc.
To minimize error, I torque the mount screws to the rail with torque driver. Still I test fire a couple shots to verify dope, and make adjustments to the table if needed.
-TL
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Nightforce, Badger, Geissele, mounts, no worries.
Edit to add Reptilia, maybe Scalarworks if Marks replacement holds together.
Mine? My failed mount’s weakness was specific to the old 30mm RDS hinge they had. I don’t think any of their other products shared that flaw.
You’ll lose your zero, son!
Only if it is a LaRue mount.
I understand that point. I guess one can do that if one has multiple rifles for long range shooting, for example. But the OP has only two rifles, wouldn’t make more sense to set them up each for a specific purpose?
I’m not criticizing. To each their own.
Now those were supposed to “Laruin” your rails according the the homos at AAC back in the day. They were having a sissy feud with nut case Mark LaRue however.
I find it impossible to believe that two different rifles would have the exact same zero, no matter how repeatable the mount may be on a single rail.
Therefore, you will loose your zero on one of the rifles.
It works if you accept the different zeros and have different dope tables.
-TL
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You could do that, but the windage is still a variable.
The dope table has windage setting for no wind too. See post #7.
-TL
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That works!
My brain doesn’t work calendars or windage adjustments. I just doesn’t. I’m all for sharing one good scope if you have a system.
Yeah I also took time to accept that the dope table is just “expected values”. There are variables at play in the field, wind, temperature, atmospheric pressure etc. One needs to be flexible and adaptive, and be quick to adjust dope to compensate.
-TL
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I was poking fun at LaRue mounts allegedly chewing up pic rails and the ensuing meltdowns from back in the day.