By dedicating the build of a rifle for this sole purpose, an AR-15 can become the top choice for a semi-automatic sniper system. Description from survivaloperations.com. I searched for this on bing.com/images
HK SL8-4. Canadian version has a wide magwell to except G36 high-cap mags. Sadly, in the US, we have to modify our SL8-1 and SL8-6 by milling out the mag slot in the upper, use a G36 magwell and also buy a G36 bolt head.