Quote Originally Posted by nsaqam
The Gibbs cartridges blow the case out, sharpen the shoulder angle and move the entire shoulder forward a considerable amount.
You don't do this by jamming a bullet hard into the lands but instead by forming a false shoulder precisely where the new shoulder will be in the FF'd case....
Your description of cartridges that were introduced by Rocky Gibbs is very good.

In fireforming a case to a Gibbs chamber the requirement is that you maintain a tight headspace for the initial fireform. This can be accomplished, as you stated by creating a false shoulder. It can however be accomplished by using a bullet seated very long and pushed into the lands to hold the case tight against the bolt. In order to get a good fireformed case the case head needs to be held tightly to the bolt face.

I have a 240 Gibbs that I have fireformed cases for using both methods. The only drawback that I have with using a bullet into the lands is it wastes a good bullet and needs a medium load of powder, Where using a false shoulder I can use a small charge of a fast powder and a cotton ball.

Here is a pic of a Gibbs before and after fireforming using 30-06 brass



To the orignial post ...... mechanically, yes you can do as you described. NOT a good idea but it would do as you described.