Plasma Cannons for White Star

I've been working on a supplement for White Star that focuses on starship weapons and modifications.  My current working draft contains forty different items in various stages of completion, and I thought it might be fun to share some of them with the rest of the world as I work on them (especially those items that I could use some feedback on).

Presenting the first in my "White Star Ship Modifications" series of posts:

Plasma Cannons

Plasma cannons fire bursts of ionized gas. Upon a successful hit, the target takes 2d6 points of damage. If the initial damage is not completely negated by the target's shields, the plasma will continue to damage the target, bypassing the target's shields completely and doing an additional 1d6 damage per round directly to the target's hit points for the next 2 rounds.

• Range: 12 8
• Cost: ???

It's a pretty simple writeup, which is what I am aiming for. Feedback is greatly appreciated. In particular:

• Is the damage - particularly the part that bypasses shields - too much? The final supplement will contain a few different starship modifications that will help to heal starship HP during battle, if that makes any difference.
• The range is the same as standard laser cannons. Does that seem like a good range? It was suggested that I drop the range a bit, to reflect the fact that the wepoan fires bursts of gas as opposed to laser.
• How much should these cost?

Thanks in advcance for any tips and advice.