To mount the Leupold VX-Freedom 3-9x50mm Rifle Scope to a Browning BAR I recommend using the Talley Picatinny Base for BAR at the first link below. You will need the 30mm High Rings with Leupold VX-Freedom 3-9x50mm Rifle Scope, and I recommend using the Leupold Rings at the second link below.
https://www.opticsplanet.com/talley-picatinny-base-for-bar.html
https://www.opticsplanet.com/leupold-backcountry-cross-slot-30mm-rings-med-matte.html?_iv_tube-diameter=30-mm&_iv_ring-height=high
The Leupold VX-Freedom 3-9x50mm Rifle Scope is recoil/shockproof and will have no issues withstanding the recoil from 30-06, as long as you use a quality set of rings. Due to the objective lens size (50mm) high height rings would be the lowest possible height rings you can use. If you have a picatinny scope base, I would recommend the NightForce ULTRALITE 30mm Titanium/Alloy Ring Set, or Warne Mountain Tech 30mm Scope Mount Rings. Both can be found by using the links below. If you have any further questions, feel free to email us at Techsales@opticsplanet.com for further assistance.
https://www.opticsplanet.com/nightforce-ultralite-30mm-titanium-alloy-ring-set.html?_iv_ring-height=1-dot-125-in-high
https://www.opticsplanet.com/warne-mountain-tech-30mm-scope-mount-rings.html?_iv_ring-height=high
I would recommend using a dedicated AR15 style scope mount, which are designed to keep the centerline at 1.4" or higher to make it easier and more comfortable to use your optic. I'd recommend the Steiner AR-15 P-Series Cantilever Mount, found by using the link below:
https://www.opticsplanet.com/steiner-ar-15-p-series-cantilever-mount.html
To mount the Leupold VX-Freedom 3-9x50mm Rifle Scope to an AR10 I recommend using a cantilever mount. The Leupold mount at the link below will work.
https://www.opticsplanet.com/leupold-177094-mark-ar-integral-mounting-system-1-pc-base-30mm-ring-combo-for.html
The Leupold VX-Freedom 3-9x50mm Rifle Scope will work for a semi auto .17 caliber. The Leupold VX-Freedom 3-9x40mm Rifle Scope at the link below has a specific rimfire reticle that would work well for that rifle.
https://www.opticsplanet.com/leupold-vx-freedom-3-9x40-1-inch-riflescopes.html?_iv_reticle=rimfire-moa
Yes. By holding the button down for a few seconds turns it off. The button is on the opposite side of the windage adjustment.