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.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.