OK, some of you guys who have SCAR17s chime in.
Is nailing a 20" target at 1760 yards with a 308 semi complete bullshit or is it reasonably doable?
I'm voting for complete bullshit
General disclaimer: I am going to ignore the whole sammich maker business since that is a little too easy and try to address the specific questions.
That is sort of an interesting question. Generally, that is a bit too far to hit anything consistently with any 308, semi or bolt. However, given enough time, it is statistically quite probable.
I have seen a few SCAR 308s be reasonably accurate, but most seem to be in the 1MOA - 2MOA range with decent ammo. There are a lot of itnernet claims of quarter MOA groups and all that, but I have a suspicion that they are just that, internet claims. My LR-308 has shot a sub-0.5MOA five shot group once, but that does not make it a 1/2 MOA gun (or me a 1/2 MOA shooter).
Either way, as far as 308 semi-auto accuracy goes, SCAR is very respectable and shooting it out to a mile is probably a lot of fun if you are the masochistic type. I've never tried to take a 308 that far though.
On the scope durability issue: SCAR seems to have a fairly shard secondary recoil impulse from the bolt slamming forward. How hard it is on guns seems to be fairly overblown, but it is probably wise to look for something that is rated for powerful springer airguns that have the same kidn of a sharp impulse in the wrong direction.
Most quality scope makers test for that, but some make a bigger deal out of it than the others.
Of the high end scope makers, March comes to mind since I recall they mounted a couple of their scopes backwards on a 50 cal just to see if it is going to budge anything. The scope survived just fine, so it will probably work well enough on a SCAR. I am not sure which configuration you are looking for, but personally, I would put their 1-8x24 FFP on it. That scope is very appropriate for the rifle. 8x is not too much, but March optical quality is very good and it is not a precison rifle anyway. You can, of course, step up to something like the 3-24x52.
All that having been said, if I were you, rather than screw around with fancy optics, I would just get a couple of fixed power SWFA scopes and save some money. For experimenting at long distance, they work fine. Tracking is good and the adjustment range is quite generous.
Personally, I would probably just put a SWFA SS 10x42HD on there with a red dot in a 45 deg mount and call it a day. Kinda like what I described here:
http://opticsthoughts.com/?p=2227
ILya