holes
Helium is a gas that is weightless, odourless, and would make a barrel lighter.
a hole
Helium.
The answer is a hole.
On the INSIDE of the barrel, they are called grooves. Together with the ungrooved areas, called lands, they make up rifling. On the OUTSIDE of the barrel, they are called flutes. These are cuts made in the barrel to make it lighter.
A flashlight
Unscrew the barrel cylinder at the back of the lighter.
A hole. When you put a hole in the barrel, it reduces the weight of the barrel. But, when you remove the hole, the barrel becomes heavier.
You have to add AIR.
A hole
A hole