Hiya
Checking for water in the barrel is simple. Just turn the gun upside down and listen!! If there is water in the barrel, you'll HEAR it sloshing around!! Having a barrel leak is not such a common occurance. Most manufacturers have good products, but small mistakes can and do happen. Sometimes a inferiorly fitted barrel plug will work fine until one day you dive very deep and the pressure then makes it leak!! Any barrel that leaks will be fixed under warranty.
MrX, try RA's NEW 6.0mm spear with a single 16mm or 18mm band!! GREAT for smaller, fast moving fish!!

Regards
miles