I got a new P223 3-9 for my stag M-4. After zeroing at 100y I lifted the zero reset dial to 0. Then used the 1/4 gradations and marked 200,300,400,500 with colored sharpies(green,yellow,orange and red)I used the ballistics for my load and confirmed in the field ( my range only goes to 400). So I go turkey hunting at my land and out comes a hog, pop him behind the ear and down he goes. I cut out the backstraps and sling my rifle over my shoulder and head for the other feeder.after I get there I notice my vertical elevation is way off.I don't know if the zero reset lifted up or the actual elevation has changed.I figure the reset would be easier while slung across my back.I lift reset back to 0 and see a turkey and 100y shoot and knock feathers off the top of his back he flies away.I go back to truck and test fire at 100y, 3 inches high. Is there any way to lock down the reset once it is zeroed like the CDS system Leupold uses . Thanks in advance

I don't think so. I had the same issue with one of my old Vortex scopes (which is why I sold it). The turrets move very easily, and if the turret cap gets raised, it can move and reset your zero. I would find one of those heavy duty rubber bands (like on a lobster claw) or something that would wrap around the scope to secure the turret in place when you carry it on your back and in the field. You can easily remove the rubber band when ready to shoot. Just an idea.

One of the design flaws of the scope. I have a M223 on my son's .243 (surprisingly the ballistics match quite well to his bullet if the .243 is sighted in at 50 yards, it will be within an inch at 400 yards when using the elevation turret with the yardage marked) and that is one thing I always have to remind him to do before shooting is watch and make sure the adjustments are back at zero.

Haven't had it lose zero yet, as the set-zero is still there, but maybe that is a difference in the monarch line versus the prostaff line?

I understand what you are saying. I usually don't need to glance at the yardage since I probably just adjusted it prior to my shot. I have had the turrets turn on occasion when sliding the scope in or out of the case but never while carrying it over my shoulder on a sling. I know how tight the tight the vertical turret is to pull up, hard to imagine that it could pull up, turn then be pushed back into place at a non 100 yard setting. If I did notice that it was in free spin I would turn it back to 100 and resecure it. I have heard from a few guys who have had the turret move as described earlier while the turret is down and in adjustment mode. That could absolutely cause your zero to be off center. I have both P-223 and M-223 scopes and I would say they operate the same as far as zeroing the the point of impact. Nikon did increase the tension in the turrets a few years ago.

Bottom line, if a turret cap somehow gets raised and turned, there are no changes to POI, just turn it back to your zero and push it down. If you look down and it is off 100 or for BDC scopes,0, turn it back, again, you should be good to go.