I'm very curious about the 5.56, too.Thanks for the info, is it feasible that it is a universal mount if the 7.62 if needed, also a point of interest on my part, what is the coax ammunition load out.
Here's what I found: http://wapedia.mobi/en/Puma_(IFV)?p=1
"The secondary armament is a coaxially mounted 5.56 mm HK MG4 machine gun with an approximate rate of fire at 850 rounds per minute and an effective range of 1000 m. The ammunition capacity is 2000 rounds; 1000 ready to fire and 1000 in storage. While this again is a smaller weapon than the western-standard of using a 7.62 mm caliber MG as secondary armament and may lack power in certain situations, it again offers advantages because it has a higher practical ROF and the crew can use the ammunition in their individual firearms as well. In situations where the lower penetration of the 5.56 mm rounds is an issue, the high ammunition load of the main gun enables the vehicle crew to use one or two main gun rounds instead. Nevertheless, the gun housing can host the 7,62mmm MG3 also."