Each Bore Tech Rifle Cleaning Brush features a cold welded core attached to a brass coupler. The brass bristles are filled all the way down. This detail helps to produce an effective, long lasting, high quality brass bore brush for your gun. Note: The 17 and 20 caliber rifle brushes are shortened to 1" in length to lessen the necessary force required to push a brush through the bore. This helps prevent against cleaning rod flex and barrel damage.