Yes, it will be usable for both however the reticle is optimized for 223, the holdovers will not be accurate with 308.
The Trijicon ACOG 4x32 does not require you to remove your front sight post. It will be slightly visible in the window but will be more of an unfocused blur.
Yes, the Trijicon ACOG 4x32 will work on a FN SCAR 17 in .308. However, this model listed below has the .308 ballistic reticle.
https://www.opticsplanet.com/trijicon-acog-4x32-red-dot-scope-w-center-amber-crosshair-308-bal.html
Yes, this is compatible.
No, because the reticle is calculated for the .223 caliber round
This should work just fine for 5.56. It might be slightly off at longer ranges, but you can re-calculate the drop markings so you know their value for 5.56
Please email us at Techsales@opticsplanet.com so we can further assist you with your question.
Yes, this is compatible
Yes, here is a link to a compatible cover:
https://www.opticsplanet.com/scopecoat-xp-6-trijicon-acog-ta-31-cover.html
It should work just fine for 5.56. It might be slightly off at longer ranges, but you can re-calculate the drop markings so you know their value for 5.56.