It definitely contributes negative buoyancy (it sinks, after all!). The unknown is what does your current BC contribute. You can measure this if you are so inclined and decrease lead accordingly.
Alternatively, the easy bet is to just use the same weight but test whether your wing is empty at the safety stop. (Purge regulator to about 500 psi first.) If you can then vent more than a few bubbles, drop 1-2 lbs off before your next dive. Repeat until it's dialed.
I would measure, but I also have access to a deep tub in which I can sink it.