Lego Space - Set 6861 X-1 Patrol Craft
Set 6861 is a fighter-type spacecraft, introduced in 1980, consisting of 55 pieces. I received this from an eBay auction in July 2012, in practically new condition with virtually no play wear; it appears to have been in a grownup's display collection.
The model has two oversized engine-gun assemblies. This is one of them, half-assembled.