You might want to build a pellet trap using something like rubber mulch. Those field targets are ok outside but I imagine you are getting lead splatter.
I have one of the refurbs, too. I really like it a lot .
You might want to give a somewhat heavier pellet a try, like the JSB Exact Heavy. These Gamo's are known as pretty powerful springers and the heavy pellet can help a bit to calm down the shot cycle, which also will make the Swarm Maxxim slightly less hold sensitive and thus more easy to shoot. The JSB pellets are as known as very high quality and accurate pellets (if your bore likes them, but most do).Btw nothing wrong with the smell of a dieseling springer, it makes me feel alive