When I first looked into it each of the outfits I contacted recommended you break the barrel in properly according to the barrel manufacturers recommendations before nitriding.
Shooting cream of wheat fire forming loads would do nothing that is going to help you at all as far as barrel break in is concerned.
The metal is not heated to a high enough temperature to cause any changes in shape.
There are essentially two processing being done, the salt bath nitriding and meloniting processing.
Salt Bath Nitriding
Meloniting
These are not coatings like cerakote, they actually treat the metal changing it's surface properties making it harder and less resistant to heat damage as well as greatly reducing the friction by smoothing out the surface roughness.
Done properly there should be no negatives to having it done. Generally the barrels will run at higher velocities with lower pressures and resistant to any future damage from rust or chemicals being used such as cleaning solvents. You should also have far less problems in the future with copper and lead fouling.
The process when done on action parts also essentially makes them self lubricating by virtually eliminating friction.
It's used in military weapons particularly automatic weapons to greatly increase life by reducing damage done by running the barrels hot. That theoretically should also significantly improve accuracy when firing groups.
