Nothing wrong in necking up 6 Rem brass! Also, made brass from 7x57 brass, but had to neck-turn the brass. PPU 7x57 brass is tough brass.
Today, I shoot a Roberts AI.
In the late 80's, I was at the rifle range and a friend had bought a new Ruger 77 in Roberts. That rifle was shooting patterns, not groups. He was so angry at the rifle. He had fired around 100 rounds during the day trying to sight in and find a good factory load that the rifle liked.
He offered to sell me the rifle for cheap, and I bought it on the spot. I cleaned the barrel, bedded the rifle, free-floated the barrel, and removed that center screw. I reload at the rifle range, and the Next time at the rifle range, I was shooting 1/2-3/4" groups with little effort with my reloads. Since he was a friend, I sold him the rifle back. 117g Sierra btsp with IMR 4350 was magic in that rifle.
On these rifles, make sure you can open the floor plate, reach up inside with a finger and easily wiggle the mag box. If the mag box is tight, then it is pushing up on the center of the action, and often this stress will ruin accuracy. Often a little filing with a square file, making the notches deeper for the trigger guard and the floor plate. Once you see this for the first time, the lights come on....you wonder why such a simple fix is not done at the factory.