They appear (to me at least) that they are setup for suppressors. Are they?
The G36 is. And I'd suspect that it's very likely that the Mexican FX-05 Xiuhcoatl is too; it's development was followed VERY closely by the Mexican Special Forces community, who had input into its design. And the Mexican boffins are working on an air-burst grenade delivery system for it similiar to the US XM25; whether a 25mm like the US version, a 20mm like the Korean, or other is unclear at this time. But I suspect that once in the hands of troops, the Zetas drug gang hitmen will have them shoirtly thereafter.