This is an early production model of the HK G-3. They're still being produced by license in some countries though not in Germany.
I have a Century Built G3. When Century first start producing them with parts kits and American receivers, there were some problems. This rifle features a rather unique bolt, and Century didn't get it quite right. Mine is from about the middle of the production run, and functions fine. It has black plastic furniture instead of wood. I bought a complete set of wood furniture from Sportsmans Guide and someday when I get really motivated I am going to swap out the newer plastic for the more attractive (if less functional) wood.
For years, the big issue with the G3 was magazines . They come in two forms, a steel magazine and an aluminium alloy magazine. Both were expensive, in the 1980's they ran about $35.00 or $40.00 per example. Then in the mid 1990's the Germans released thousands of magazines, in unissued condition, from their war reserve. You could buy the steel mags for about $6.00 and the aluminum alloy magazines for $2.00. I bought about 50 of the latter and another 20 of the steel magazines. I knew this was going to be a one off opportunity.
The G3 aluminum alloy magazines were cheaper of course, and they were lighter. I read that they
The steel magazines were much more robust ,and significantly heavier. Because they cost more, I didn't buy as many of them but I laid in a good supply.
With a semi-automatic rifle, it pays to have a lot of magazines. They don't last forever, even with good care. Feed lips get bent, springs go bad, followers get bent. Some of this stuff you can repair, if you have the appropriate parts. Sometimes though, you just have to put a magazine in the scrap box and cannibalize it for parts down the road.
The HK G3 chambers the 7.62X51 NATO round. I've used both that and Winchester .308 in my rifle without the slightest difficulty. Overall, the G3 is a good, stout weapon that you can rely on. Parts are a bit hard to find but you can still do it.