Berry 125 grain flat nose 357 ok to use in 9mm?

Your seating depth will be determined by the full diameter bullet shank where it breaks over into the nose ogive.

You will have to seat them probably about a 1/16" inch of the ogive out of the case to prevent the full diameter bullet shank from jamming into the rifling.

Do the 'Plunk Test' and continue to seat deeper until they will fall in the chamber full depth, and the fall back out.

The other potential problem you could run into is that .357" bullets won't chamber at all in your gun if it has a tight chamber intended for .355" bullets.

You need too load a few and see if they will drop in the chamber.

Your load of 5.3 Power Pistol is 0.4 below the 5.7 Max according to Lyman # 49, so you should be good if they will chamber.

rc

I've heard that some Berettas have large bores in their 9mm (92). Might be awesome in those.

The larger .357 bullet in the .355 bore of a 9mm would cause higher pressure. I would either load down from max, or get a bullet sizing die from Lee to squeeze them back down to .355".

A change of components warrants backing up and starting at the standard 10% less than max charge. Based on the info in this thread, that would be 5.1 gr.

So it would be smart to load 5 or 10 at 5.1 just to make sure. If you get fantastic velocities out of range for a 124-gr 9mm from your length of barrel, back it off some more.