"Feels full" is kind of a misleading statement since those bottles are always full. The are full of a substance that looks similar to concrete and is very porus. The acetone and acetylene gas are suspended in that substance in the bottle. Therefore weighing the bottle without knowing what it weighs empty is kind of a wasted effort.
I also have not seen a bottle with that fitting, but all of my bottles are sourced from a single shop, which uses the same standard. I have a lot of spare parts for my type, but not yours.
David from jax