Hello, 270. There should be a folded tab on underside, plus folded tabs for each "ear". These are tightly tucked in place so kind of hard to see. There has been reports of the fine black heavy sand as sold by Sinclaire and others having a tendency to leak thru seams..I use this heavy sand, and have had no leakage in over 20 years.
I think they suggest rubbing beeswax along seams if problem.
Don't fill too hard, if your a bag squeezer, and especially on front reat bag..this can cause accuracy problems.