Cleaning rods (including pull through cords) have probably ruined more barrels than shooting them thousands of rounds.

As you can see I took 30.06 cases and made these and they fit are best made with a lathe when it comes to opening the bottom of the case.

I purposely made the necks longer than the 30.06 length so it would go into muzzles further. I wrap patches around bronze or nylon brushs coated with what I will be cleaning with and ease the brush/patch into muzzle gently making sure not to drag rod on inside of bore and then ease the case guide into place and while holding the guide with left hand I run the rod back and forth multiple times.

So if you have tired 270, 280, 30.06 cases you can recycle them for your friends if you happen to have a lathe or a buddy with one.

Oh yes I also determined the work well on 35 cal bores and larger though they are originally made for 30 cal. Remember the barrel you care for today will take care of you for many years if treated with TLC.