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Sounds like a reasonable idea to me, although I have not tried it.

To understand why this works, you need to understand that brass (like most any material) stretches under stress in two ways. These are called 'elastic deformation,' which is reversible like stretching a rubber band, and 'plastic deformation,' which is permanent like swaging a lead bullet. If the amount of deformation (expansion) due to firing is small, i.e. with a 'tight' chamber, most of the expansion will be elastic. The looser the chamber, the more plastic (permanent) deformation you will get. Remember that with almost any reasonable load, the pressures will be high enough to force the brass out in full contact with the chamber wall, sealing the chamber and acting as a gasket. This is one of the primary functions of the brass.

With handguns having 'sloppy' chambers relative to the unfired case diameter, you will get more plastic deformation. Provided that you are not loading above normal working pressures, you will always get some elastic deformation, so the brass will spring back some after it is fired. It will spring back to the dimensions set by its elastic deformation limit.

Once the brass has been fired, and the bottom of the case not sized, when it is fired again IN THE SAME GUN that lower portion of the case will not undergo significant additional plastic deformation, i.e. it will spring back to pretty much the same as-fired dimension. Repeated sizing and firing of brass causes it to work harden, and this eventually causes failure. The necks of many cases are annealed (which softens and intentionally weakens the brass) so they can stand more sizing-expansion cycles than the rest of the case.

The IN THE SAME GUN thing is important, since the dimensions of the fire-formed and unsized brass will often exceed SAAMI limits, particularly if your chambers are loose. This is not a problem if you are re-firing in the same gun, but it can be if you want to use the ammo in a different weapon. I think that Marshall said something on this site about how the Lee Loader (for example) only resizes the case neck, and therefore is recommended only for use to reload for the same weapon.

According to an article I read by John Linebaugh on the sixgunner website, for the 45 Colt the problem of sloppy chambers is quite prevalent and is the result of two factors: the chambers are often made at the upper end of the SAAMI limits to ease chambering of cartridges, and current-production brass is at the lower end of its dimensional limit. This results in excessive expansion, and therefore shortened case life. It is an interesting article, "The 45 Colt: Dissolving the Myth, Discovering the Potential." You can find the article at:
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