Normally five, but additional uppers and caliber changes do not count against that number (e.g., an AR with a 223 upper and a 22 upper counts as one). There are also exceptions for hunters (+1, I think) and collectors, though what you are a collector of must be very specific, such as, "HK pistols from 1980-2000".Are their any limits on how many firearms you can own in the Netherlands?
I am currently collecting the parts to do the UMP conversion. I will post pictures as that moves forward (in the Long Guns section).Very nice collection! You just need to convert that USC to a UMP. Where do you shoot there? I would guess it is rather restricted. I lived in Amsterdam for several years, but my HK colection stayed in the US and I never explored shooting there. Fantastic country even if you can only own five guns, we loved the NL!