From the Thompson Center Reloading manual (yeah, there really is one) they make the statement:
"First time fired cases (fire forming) should be loaded with 10% less powder than standard loads. Successive loadings should be full length sized."
They do however, give what I believe are reduced loads and possible fire forming loads- they really don't comment on it but noting the loads are a major difference, you might consider trying it. Using a 158gr lead bullet 9.0grs Blue Dot =1190'ps, Federal 215 primers.
Same bullet, 12.0 grs 2400, CCI200 primers=1181'ps.
The velocity is out of a 10" barrel. Blue Dot is used a lot for fire forming brass so this data may be just what yer looking for. When I fire formed my 357 Herrett brass, I went with max loads and never looked back. The brass will fire form long before peak pressures are reached and there was zero difference in bullet impact or velocity between fire formed brass and virgin unformed brass. YMMV.