I didn't shoot that gun much, but it would hold 2" groups with iron sights, (and with my eyes it would certainly do better with a scope!) but I didn't test it with scope - there was a QD scope mount with it.
Ackley improved chambers are cut so that you can use both factory loads or expanded cases. The advantage of the sharper shoulder is lower pressure or more bullet speed, at the same pressure. If Ackley chambers are not cut correctly they can cause excess headspace with factory loads. But the 7x57R headspaces on the rim, so there is no issue with shooting normal factory loads in any rimmed Ackley chamber, velocity will drop maybe 30FPS and the case will just move out to fit the sharper shoulder. The 7x57R is a very common European chambering, ammo is available from Norma, Sellier&Bellot, RWS, etc.
My Merkel shoots S&B or Hirtenberg 175 gr. factory loads at right around 2400 FPS.