A firearm includes a support block having a forward end and a rearward end, and carrying a receiver on a top surface thereof. A rearward barrel guide having a thrust coupling extending radially outwardly therefrom, the thrust coupling engaging an engagement element located at the forward end of the support block, thereby aligning the rearward barrel guide with the support block. Also provided is a barrel having a breech end and a muzzle end, the breech end is received through the rearward barrel guide and coupled to the receiver. A forward barrel guide is fixed to the barrel intermediate the muzzle end and the breech end. A handguard assembly is received over the barrel and coupled to the rearward barrel guide and the forward barrel guide, stabilizing the barrel.