I used to buy those ply tip weight boxes, and glue them all together. Lately, I have simply used a scrap block of balsa, about 1" square. Drill a 1/2" hole partly through and glue it in the wing. Finish with a ply cover. It holds some .45 caliber lead balls from my muzzleloader rifle. I can add or remove the lead. Simple, fast, and no cost.
Floyd.