I had a rifle like that. If it's German, they're rounding up the 5.56mm to 6mm and it takes a .22 BB cap and the chamber is too short for CB shorts. I slugged the bore on mine and it was a perfect .223" so I had the chamber cut longer for .22 Short. It's wickedly accurate and worth having opened up to .22 LR.
At the time, 22 years ago I had a 5 year old duaghter and I didn't want anything more powerful than the .22 short to teach her to shoot. Over the next several years she became an amazingly good shot and still has this rifle.
I planned to use it to teach my granddaughter to shoot but I bought a pink chipmunk for her instead. I really like starting family traditions...
Anyway slug the bore and if the dimensions are right, you could have the chamber opened up for cheaper ammo.
I was talking with a German guy about it and it seems these turn up in estates over there all the time and half the time the family won't pay the transfer tax (about $50 USD) so they turn them in. I was concerned about ruining the collector value but after hearing this, I think I did the right thing.