I've never had nor heard of headspacing problems with a KK300, ours shoot superbly with RWS R50 or Eley Tenex, and I know people who shoot Lapua with them. They are designed as a very ammo tolerant rifle. We've had two, and I still have one, both before, and now the one I still have extracts and ejects each shot neatly into a 6 in square tupperware box if the bolt is lifted with the same effort each shot, (saves picking up empties!), try that with an Anschutz!

The only time I've seen a KK300 not extract is with an unshot live round and that is because the bullet is stuck in the rifling, but that should be a very rare experience.

We clean our rifles after every shoot with a few dry felts to remove carbon, and wipe out the breach and bolt face, perhaps once a year I give them a good scrub out to remove any lead build up, (whether they need it or not!) this is the recomended Walther cleaning regime.

Walther use R50 for its new Rifle group testing. We have never bothered to batch test, and we both shoot RWS R50 exclusively, and have never had a misfire or failure to extract from either rifle in five years, and we both shoot 5K+ a year.