This was posted on trueachievements.com by Ayerow, so thanks to him.
Before you start you have to make sure you spawn in as a the default pirate or the kills wont count.
Once you've done that head on over to the battlegrounds and raise the flag, then Just let the zombies/plants bunch up around you then blast them away. you should be able to stay alive long enough to finish both the spyglass and the scattershot
Note: In case you didn't know you need to aim with LT to switch to the spyglass &
The Scurvy Scattershot ability is when the Pirate is sitting on a canon shooting.