I too once set about assembling an SPR, with the qualification of it being a more accurate, longer range semi-auto in our weapons battery.

Using the (now) classic model of the MK12 type SPR, I soon realized that, though a monumental evolution at the time, it's truest incarnation is a bit outdated.

Though I stuck with the 18" barrel, I went with a more modern, slimmer fore end, a 1-6 LPVO, and a collapsible stock.

Things like an LPVO and a stock that's lighter and has adjustable LOP represent the modern advancement of the concept, in my opinion.