I may have posted this before and it was lost in the Board shift. BATFE now says it is permissable to mill a groove the area of the muzzle along the side of the barrel rather than dirlling the "moon-size" hole in the high pressure of the chamber. If my calculations are correct the muzzle area is a little under 5". A .75 in wide, 7' long groove would satisify the feds. An "obstruction" still has to be welded in the barrel, not an "obstruction," nothing said about a bar. A nut welded to the side of the barrel would suffice. This is specially helpful with a Type 10, you can still store the parts in the barrel as designed and the groove acts as a viewing port.