Weapons like this have been around since World War II (e.g. the Finnish L-39). Assault cannons in Shadowrun 'feel' more like payload rifles than anti-material rifles, and this seems more like the Barrett Model 121 (Arsenal, p. 28).
If you want to "build" a Shadowrun anti-material rifle, I recommend changing any sniper rifles stats by: +2 Damage, -1 AP Mod, and x2 cost just as if was firing High-Power Rounds (War!, p. 156). with High-Power Chambering (War!, p. 156). Maybe crank up the stats a bit more and drop the Ammo to 3 or 5 to season to taste.
Strictly by canon you would probably be using Anti-Tank Rounds (War!, p. 156).
(I'm personally ambivalent at best to most of the War! stuff,, but it keeps things simple to reference it until something better comes along.)