Complex sentence: Towards the end of the production run, a prototype SU-122 was built with the same ball mantlet as the later SU-85s, but are easily recognizable by the thicker, shorter gun barrel of the 122-mm M-30 howitzer.
Split into simpler sentences: Towards the end of the production run, a prototype SU-122 was built with the same ball mantlet as the later SU-85s. These prototypes are easily recognizable by the thicker, shorter gun barrel of the 122-mm M-30 howitzer.