Funny you should ask this. A good part of my Sunday range day was spent on fire forming new brass.
Simple answer: When applied to new brass, No. Proper fire forming should be done with a bullet (preferably flat based) jammed into the lands.
If you cannot reach the lands then there is another more labor intensive way that still requires a bullet.
If the brass has been fired then the damage is done and oatmeal or some other cereal can be used.

 

If you want to fireform a set of cases, you need at least 55K PSI of pressure in the chamber.
I don't see how you could do that <easily> without a bullet.
I do know of laboratory equipment that could do it, but bullets are very much lower on the expense scale.

 

10-15 grains Unique (careful...****'s REAL fast compared to rifle powder), Cream-of-Wheat to fill the rest of the case OVER the powder, then a dollop of Crisco over the top in just the neck, as a place holder to keep Cream-of-Wheat in place. Also, depending on what you are trying to form, you may need to neck UP, then partially size the neck to create a small false shoulder on the neck to keep the casing in a slight crush fit so the firing pin has resistance enough to get good ignition. Poor ignition will show up as an incompletely formed case, and unburnt powder and C-o-W all over the action when you extract.

Chamber and fire. OUTDOORS.

Properly done, the yield is a fairly completely burnt charge of Cream-of Wheat, a nasty ass barrel, a formed casing, and zero damage to the rifling or chamber.

But READ THIS:


http://www.6mmbr.com/260AIforming.html


-Nate

 

But READ THIS:


260 Ackley Case Forming


-Nate

And this:
https://sierrabulletsblog.com/2016/09/14/reloading-101-fireforming-cases/
If done properly, case life will by extended by quite a bit.

 

Or your could get one of the hydraulic dies from Whidden or Hornady.

 

That's a good one, lukino. I hadn't seen it. I don't think everything Sierra does is perfect, but in their publications, they do generally take a safe, sane, and conservative approach to reloading.

 

6mmbr.com or accurateshooter.com,check out “6mm ppc” or “6ppc” down the left column on home page. It explains to the readers how to fire form 6ppc cases.

 

Another thought is to use your own home cast bullets for fire forming. Zero impact on riling yet sufficient pressure to form. If you don't cast you can purchase inexpensive cast bullets.