Hello NitroX,

Yes, I use "Backer Rod" as a filler. Backer Rod is a closed cell foam rod that comes in 20 foot and 50 foot lengths in various diameters; 1/4", 3/8", 1/2", 5/8", 3/4", etc. Its used to fill the gaps around window frames during initial installation to prevent drafts. It is somewhat resilient, but very light. I used 5/8" dia rod, cut to 1-1/4" long, in these reloads. It weighed only about 1 grain.

I put a touch of bullet lube on my fingers, and transfer it to the rod while handling it to make the outside of the foam rod a little slippery. I take care not to use too much lube, or get any of it on the end of the foam rod where it could touch the powder. I then carefully "screw" it through the case neck by rotating as I insert it. I compress it "ever-so-slightly" and "carefully" as I rotate it into the neck and all the way down into the case until it pushes against the powder. With the bullet seated, its length is compressed about 1/8" and the foam rod holds the powder firmly against the inside base of the case.

Its a closed cell foam, so you have to be careful NOT to compress it too much, otherwise you will fracture the cells and it wont spring back to full diameter. I also use this same 5/8" with my 577-500 bpe. I little compression to get it through the neck, and it "puffs" back to full diameter inside the case body. It works great, but again, be careful not to squeeze it too much. Of course it works effortlessly in a straight wall case, like the 500 bpe, where I use a 1" piece that weighs about 8/10 grains. It drops right in on top of the powder.