The reticle in this model is optimized for 223 Rem. It can still be used with 308 Win. however the holdovers will be different.
If you are looking for the models that have reticles specific to those calibers then you will want MPN:AR741840 and MPN:AR741840C.
Bushnell covers this Bushnell AR Optics 4.5-18x40mm under there Ironclad Warranty. I recommend contacting the manufacturer regarding the specifics of their warranty.
The Bushnell AR Optics 4.5-18x40mm Riflescope has an etched reticle and can be used with out batteries. If you get the illuminated reticle model, the reticle will still be visible without batteries but will need batteries installed to work the illumination.
There are many options to choose from and it mostly comes down to preference. How far you want to shoot, if you want a small or large optic, etc. My suggestion is to get something that has a .308 reticle built into the scope such as the Trijicon ACOG TA01. A link to that optic can be found below.
https://www.opticsplanet.com/trijicon-acog-4x32-red-dot-scope-w-center-amber-crosshair-308-bal.html
The Bushnell AR Optics 4.5-18x40mm Riflescope with a BDC reticle is an etched reticle.
I would suggest the American Defense Manufacturing AD-RECON Scope Mount with 1 inch rings for the Bushnell AR Optics 4.5-18x40mm Riflescope. However, your A2 front sight post still may be in the way so I would consider getting a low profile gas block. The mount can be found here:
https://www.opticsplanet.com/american-defense-manufacturing-ad-recon-scope-mount.html
The turrets do not lock. According to a customer review: The adjustments have firm positive clicks
It is giving you both answered if your going to adjust is by MOA its 50 MOA or 18.0 for Mil if your adjusting by Mil
No there is no locking turret on the dials.