Has anyone that has purchased an FN 13" barrel assy for the SCAR17 noticed any unusual roughness of the travel of the gas piston? I was about to put mine on my SBR but noticed a distinct metal on metal feel when I manually worked the gas piston. I compared it to the piston of the 16" stock barrel and there was a noticeable difference in the ease of travel? Maybe it is one of those "need to work it in" items. Also, has anyone had difficulty in taking off the flash hider on the 13" barrel? I have tried numerous means other than heating and can't get it to budge.