Complex sentence: Like the Vickers, the barrel was surrounded by a 105 mm diameter heavy water-jacket for cooling, which also acted as the frame within which the barrel recoiled on firing, and which the fixed portion of the muzzle booster was mounted on.
Split into simpler sentences: Like the Vickers, the MG 08's barrel was surrounded by a heavy water-jacket for cooling; the MG 08's component measured 105 mm in diameter. The cooling jacket for both ordnance designs also acted as the frame within which the barrel recoiled on firing, and which the fixed portion of the muzzle booster was mounted on.