I've done lots of fireforming and my experience has been very positive.
The photo is 243Lapua brass being fireformed to 243Ackley
I've done the same practice with 22-250 to make 22-250Ackley,
Used this for 20PPC ... 20BR....20BR Improved
I use 700X powder in every caliber, cream of wheat poured level with top of the case, compressed with an allen tool that fits the neck as tight as possible and compressed to the base of the neck, a pinch of polyester fiber fill which is rolled between wet fingers and stuffed into the neck. I then use that allen tool to compress it down flush with the top of the neck.
Powder charges are started low and worked up while watching for pressure signs on the primer flatness/cupping. While fireforming, the barrel can get warm, so I shoot 5 or 6 rounds every 10 minutes usually in my backyard into a post hole to muff the blast.
(((((( Here in Alberta, covid is at a very bad level with hospitals at near collapse based on local news. The government is pushing for everyone to get vaccinated with incentives like $100 gift certificates and loto draws. Personally I havn't been vaccinated. The vaccine is not mandatory to the public. However, many other companies, schools and business's have made it mandatory. The noose is tightening with none vacineers not being allowed into public places.
My wife is 24 year RN (registered nurse) has handed-in her resignation. "Time will tell what to do" ))))))