Complex sentence: In May 2008, Smith & Wesson introduced their first AR-15 rifle in new caliber, the model M&P15R, a standard AR platform rifle chambered for the Russian 5.45 × 39mm cartridge, however the model was soon abandoned due to poor sales.
Split into simpler sentences: In May 2008, Smith & Wesson introduced their first AR-15 rifle in new caliber, the model M&P15R, a standard AR platform rifle chambered for the Russian 5.45 × 39mm cartridge. As a result, the model was soon abandoned due to poor sales.