Im one part away from finishing a current Mega .308 build. Iv decided to go with a Rainier Ultramatch "Shilen" for the barrel . My question is 18" vs 20" ....the gun will be used mainly as a bench/prone shooting weapon shooting steel out to 800 with the occasional 1000 shot for fun. I plan on hunting with the weapon as well from a prone or blind position. Im not worried about weight just seeing what your thoughts would be between the two different lengths. velocity loss? accuracy? any thoughts or ideas would help thanks!