BMK Modelmarine.de Shop has released a brass barrel upgrade for the 28cm main guns of your Academy 1/350 Graf Spee. This set of 6 brass barrels is machined to BMK's high standard, with drilled out muzzle and mounting pin in the rear.

This set of barrels are even better than the nice plastic ones included with the kit- the kit barrels have a nice slide molded, open muzzle, but are too large in diameter. These barrels are correct in shape, and are just the thing for you Academy Graf Spee

This barrel set (A6350KM28052) retails for 9.00 Euros, or about $13.30. You can order them direct from the Modellmarine Shop or where ever BMK accessories are sold.