I don’t have one caliber that ever gets filled up with smokeless like black powder. What do you do? Nothing. 
I either put some cotton in and tamp down or use a wad which works for straight wall cases but not bottle necks. Some shooters I know just do nothing. Add powder, apply bullet.

Long ago, I found a Victorian overstuffed chair at the dump.  It was unrestorable, but I ripped open the cushions with my trusty Scout knife (yeah; that long ago) and filled a shopping bag with the Kapok filling.

I don't use it often; only with cast bullet smokeless loads in cavernous or long cases.  A little pinch of the stuff, tamped down with a pencil eraser, expands to fill the cross section area of most brass shells and keeps the powder against the primer with normal handling.

The Kapok is some kind of fine fluffy orange colored plant fiber, like dandelion parasols, and is instantly consumed when the powder burns, so there's no obstruction potential.

Thanks to all for the replies. I use either cotton or a gasket wad like Walter’s. I’ve also use beer cardboard coasters.

I used all my kapok up.  Now I use closed cell foam backer rod.

I buy it at Lowes or Home depot.  Get the diameter that fits/ fill the body of the case.

For 577/450 with its .577 or so body, I use 5/8",  Cut a length and roll it between you fingers and insert in the 450 neck.  Push down with pencil or dowel. 

Experiment to get best length.  So I use a long enough piece that I get about .100 compression.   

I use this backer road with blackpowder and smokeless powder.

Do NOT put a wad down on the powder and leave an airspace between the wad and bullet. That is a sure situation for a ringed chamber.

Amaranth seed makes an excellent filler in loads.  Readily available in health food stores, they are spherical seeds about  one mm in diameter and meter neatly thru a powder measure.

CHRIS

Deadeye Bly wrote on Jan 26^th, 2026 at 9:31am:


Especially if the it leaves a cylindrical airspace...