According to Bill Calfee, the problem with 52s was the receivers were machined before heat treating, and the receivers could warp.
Regardless, my 52D was dead straight; we checked before fitting a new Shilen BR barrel. Both the receiver threads & front of the ring were true to the bolt raceway.
Having said that, in my 4-position days, it was never as accurate as my older 52 with the Titherington barrel. I always figured that was due to the factory barrel, and so it proved. With the new Shilen ratchet barrel, the first 400 rounds fired in matches with the D were all 10s, using the somewhat forgiving IBS 50-yard benchrest target. Shot indoors. There were X's of course, I just didn't keep count. Then it threw an 8, which I blamed on the ammo.
Good enough action. Though contrary to prevailing opinion, I don't think the action is all that important in a BR rifle, if it doesn't have a particular defect. Aside from ammo, I think it is the barrel that matters most. I realized this is heresy, but there you are.