You can make dandy shaders from chrome plated brass sink drain pipe. Sand the chrome off and you have brass shaders. I use a set for my longrifles. You can also by sheet brass or copper and roll your own. If you use the pipe, you'll have to cut a slot the length of it so it'll go over the barrel, maybe about 5/8" or so wide. It depends on how big your barrel is. You want tension on it to help keep it in place. You can also lash it down with rawhide laces or a velcro strap.
For my chunk gun, I rolled two shaders from sheet. This rifle is a halfstock and I milled narrow slots on both sides of the barrel so that the front shader snaps in place without using straps. If you don't cut the slots, you'll need to drill and tap your barrel for small screws that the shader can rest on.
Some shooters in my club use plastic tubing, it just doesn't look rustic enough. Some chunk gunners use shaders that are barrel length which works quite well. But, if you shoot fairly rapidly (which you don't in chunk gunning), heat can build up, especially with the thinner barrels and cause sight distortion. This is worse if you're shooting out in the sun on a hot day.
Shaders are worth the trouble if you shoot in the sun a lot. You have a more consistent sight picture. One drawback is the change in your rifle's balance when shootin offhand. My shaders are not big, but the gun is definitely a little muzzleheavy compared to when not using them.