years back when carbons first ended up the Guip method of mfg where they were different directions of carbon wrapped vs. the pultruded, guys were using everything to weight... some did salt, pepper... lots of jokes about those ideas!
I used .095 weedeater, 2 sections doubled over and inserted in the hollow back of an insert.
Cannot remember what it weighed, but was close to 600 gr. with 5575 and a 29 gr alum insert and a 125 gr. head in those days.
Tried weight tubes and got horrific bad flight. Sold them.
Been using brass inserts ever since without looking back!