Complex sentence: While this cartridge hasn't become a best seller by any means it still remains today, being overshadowed by its bigger and more potent relatives the 45/70 Govt' and the 450 Marlin.
Split into simpler sentences: While this cartridge hasn't become a best seller, it still remains today. However, it is overshadowed by its bigger and more potent relatives, the.45-70 and the 450 Marlin.