When I had my upper built by Tony (Tromix) we discussed barrel length at length. It seems the .458 SOCOM gains very little velocity past 16-17 inches. Some sure, but not enough to offset the inconvenience of the longer barrel. My 17" barrel throws 300 gr. X bullets at 1755 fps and 250 gr. X bullets at around 2060 fps. By going to a 20 or 24 inch barrel you would be lucky to gain 150 fps, but look at what you lose in portability. I also want to point out that I am one of those lucky guys that seem to get the "slow barrel." In regards to the vels others have gotten out of their .458s with the same load and same length barrel, mine seems to be about 100 fps slower than others. Just one of those things that cannot be predicted and is totally the luck of the draw even with the premium barrels that Tony and Marty use. Accuracy, much more important IMO than velocity, is outstanding, easily shooting between 1.250 and 1.750" five shot groups at 100 yards and that with an EOTech sight. With the 6.5-20x scope from my M15-A4(T) it has broken MOA many times.