TexasMac's Web Site
By Wayne McLerran
Updated: 7/28/13

Resizing cartridge cases will work harden the brass and increase the
chance of it eventually splitting or separating, but there are other good
reasons for minimal resizing or not resizing at all.  Following is my
viewpoint on the subject.  While reading further, keep in mind the
discussion is for black powder cartridges for single-shot rifles, but most
of the comments will also apply to smokeless ammo as well.

As with just about every subject there are pros and cons to consider.  If
the ammo is used for hunting it’s a good idea to full length resize for
adequate bullet neck tension and to ensure the cartridge easily slides
into and out of the chamber which may be slightly fouled from previous
shots.  If the ammo is being fired in more
than one firearm, full length
resizing is also recommended to ensure the cartridge will fit chambers
with slight dimensional variances.

Although long straight-wall cartridge cases can stretch, especially those
using compressed powder, if the firearm uses a bottleneck cartridge,
due to the shoulder the case is more likely than a straight wall case to
stretch when fired.  For additional discussions on the subject see
Stretching & Separating in Black
Powder Cartridge Rifles.  If the case
does stretch, full length resizing will not only reduce the diameter of the
main case body and neck but also set the shoulder back slightly.  The
result is that some of the brass will be forced to the neck by the resizing
die, lengthening the neck and the overall case.  Sooner or later the case
neck will need to be trimmed.  Therefore, each time the case is used
and full-length resized, brass migrates from the main body to the neck,
thinning and weakening the main body of the case, eventually resulting
in case separation, typically in front of the thick region forward of the
rim.  This is better understood by high velocity smokeless shooters but
also applies to black powder cartridge shooters, only to a lesser degree.

It’s always been my viewpoint that, for maximum accuracy, the
dimensions of the loaded cartridge should match the chamber and throat
dimensions as close as possible, resulting in minimal bullet expansion and
distortion and maximum alignment with the chamber and bore.  
Therefore, if the brass is being used in only one firearm, the best
practice is to never full-length resize after initial firing, commonly
referred to as using “fire-formed” brass.  But depending on several
factors including dimensions of the bullet, chamber neck, throat and
bullet seating depth, minimal neck resizing may be necessary to hold the
bullet under slight tension and proper alignment.  For those shooters,
and I count myself as one of them, that “slip-fit” the bullet by hand with
very little or no neck tension, some neck-only resizing may still be
necessary for bullet alignment.

If done properly, annealing (heating the brass to soften it) can reverse
work hardening of the case neck, but for safety reasons is definitely not
recommended for the main case body.  For more details on annealing,
see to the article titled
Annealing BPCR Case Necks.

Wishing you great shooting,