Well, starting
here, the FF tube is probably the first thing I'd change. I'd lean more towards something like the
Daniel Defense Lite Rail. I'd also prefer a cantilever throw-lever scope mount like the
Larue SPR or
SPR-E to the traditional rings on the issue gun. I'd use a collapsing stock like the
Magpul UBR or
Vltor Emod. For barrels I'd prefer a Noveske as (current market aside) they are available in several profiles and lengths. I'm leaning towards a 12.5" since with the right ammo in 6.8 the 12.5 can be a 200+ yard gun. Finally I'd finish off with something like the
Leupold 1.5-5x MK4. I'd also like a relfex mount can for it that sits back over the barrel to reduce overall length of the can/rifle combo, like the
Surefire FA68FR.
So basically it wouldn't look anything like a military SPR, but it would serve the same basic function. With a 16" barrel instead of the 12.5" I'm leaning towards, and perhaps a more powerful optic, I'm sure the 6.8 would have at least the same effective range.