If the factory bullet slides freely in a fired case neck, then you have no neck issues. If not, you might be able to correct it with a slightly larger expander.

It's my policy also to expand necks oversize and then size then down a bit at a time until the bolt closes with a light resistance. This is especially important if you spot, for instance, that the primer has partly backed out of the case after firing. It's filling the excess headspace. I used C-H tapered expanders to over-expand.

If the necks split on expanding, (not likely but possible), you can either accept the failure rate, try another brand of case or anneal first. I use moulten lead, 5 seconds MAX - NECK AND SHOULDERS ONLY. The way to ensure only these get treated is to have a shallow tray of moulten lead. A lead shotmaker was ideal for me. I also made up a heat-sink, being a thick block of brass with a case sized hole in the middle. This was then cut in half and each half mounted by a thread to a vice-grip jaw. Case's that had been treated could then be quick-released into a bucket of water to stop any further heat transfer to the case body or head especially. You must leave the SPENT primer in, by the way, when you do this.

My bore was .358 and Hornady bullets in that caliber worked very well. I never used a pistol bullet to fire-form. The 9x57 case was originally made from an 8x57 Mauser and I would think they're close enough, (see cartridge drawings available on the net), that one will make the other.