Rule 2b states: "Supervisors will supply a drop mass (50-300 grams) that will be placed in a 500-591 ml plastic bottle..."
So am I to understand that a mass of 50 - 300 g (25 g increments for regionals) will be placed in the bottle and the total mass will be the "added mass", plus the bottle and any carabiner/clasp used?
With 50 g of mass in our bottle, the whole mass was about 87g. So when we get to the competition, although we can measure the mass before we drop it, we can 't actually prepare or a given mass, as the mass of the bottle/carabiner will be different depending on what the event judge brings?
I agree with your interpretation that the drop mass is not the total mass of the bottle + attachment.
It looks like the writers tried to make it easier by specifying the drop mass will be in 25g increments for regionals and 10g for states but this was made effectively useless when the unknown variable of the bottle and attachment method was added. The last line specifies the total mass including attachment mechanism will be posted after impound.
If I were you I would submit a clarification.
Maybe the rules writers will realize the (possibly unintended) difficulty with having the attachment variable and change the wording such that the total
mass will be between 50 ~300g and will be in in 25g increments for regionals and 10g for states. Since I would expect most supervisors to use a plastic bag full of sand for the drop mass amount, it can easily be changed to compensate for any attachment and get a nice even number for regionals and state.