The newest addition to SM-1's line of barrels, this 1-piece All-Aluminum design reduces weight, but still incorporates their performance-enhancing inner-diameter sleeve sizing system! The Single piece Aluminum Barrel is manufactured to the same precision tolerances as their top-of-the-line 3-Piece Stainless System, and is every bit as accurate. Unlike many mass-produced barrels today, the SM-1 is built in small batches by a Southern California manufacturer who supplies several local teams. Its unique 1-piece All-Aluminum design incorporates a barrel-sizing sleeve system that's way ahead of its time! Ion/Impulse Threaded. 14 inch.