I recently acquired a FWB 603 with a laminate stock, makes a good comparison to the 603 Junior model that I already had.

Weight is the biggest factor, the full size 603 is considerably heavier ( 5+kg to just under 4kg for the Junior)

The Junior version does not have the anti vibration tube

Apart from the anti vibe tube and shorter sight radius the Junior has the same superb trigger, sights, adjustable stock and barrel as it’s big brother.

Junior by name but still has all the attributes of the full size rifle.

https://flic.kr/s/aHsky3fbvh