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SEATING DEPTH and CARTRIDGE OVERALL LENGTH (COL)
QUESTION:
ANSWER:
The maximum COL is
with two drive bands in the case neck and the mouth of the case above the second
from last drive band, as in A below. The minimum COL is as in B
below. The end of the ogive must never be inside the case neck and the
mouth of the case must be below the end of the ogive. The measurements for
each bullet are on the Technical Data pages and are given as a minimum
measurement and a maximum measurement to which the case length of the particular
cartridge must be added.
QUESTION:
I find that, when loaded with some types of GSC bullets, the
cartridge has unacceptable runout. I have also noticed that, on some
cartridges, the bullet noses were bent. With one brand of die sets, the
seater die seem worse than another make. Have you also found
this?
ANSWER:
Yes. On some brands the stem that
seats the bullet into the case has to be modified. What happens is that
the seater plug pushes on the tip of the bullet as in A below. That
allows the tip of the bullet to contact the flat surface at A anywhere and the
bullet can assume an angle as it is seated. The seater should grip the
bullet at B around the ogive because that allows the bullet to be centered in
the case.
Modify the seater plug at C by machining a hole as shown. It ensures that all bullets are seated by pushing the bullet by the ogive and not the tip. Ensure that the seater plug machining is perfectly concentric, otherwise it will still cause runout when the cartridge is checked.
QUESTION:
It is recommended to seat bullets off the rifling to prevent
pressure spiking up to dangerous levels. What is your recommendation for GS
Custom Bullets?
ANSWER:
Treat our older HP bullets, without drive bands,
as you would any conventional or grooved bullet.
This does not hold true for GSC drive band bullets in the HV, SP and FN ranges.
The good news is that lab testing done at Somchem Ballistic Laboratory in South Africa, showed that loading GS Custom Drive Band HV, SP and FN bullets, in contact with the rifling, or off the rifling, did not make any appreciable difference to speeds or pressures. It is therefore not a problem if load development with HV, SP and FN bullets is started with bullets touching the rifling, if the magazine and action length will allow this. HV, SP and FN bullets are not as sensitive as older designs to speed variation. Tuning for group size is done primarily by varying the overall length of the cartridge.
There are two considerations with pressure and COL, if all the reloading components remain the same. When loading with conventional smooth or grooved bullets, pressure increases as the COL becomes longer and the bullet approaches the rifling. At the same time, pressure is decreasing because the bullet is seated further forwards, creating a greater volume within the case. With drive band bullets, the COL pressure component is greatly reduced. The chart below shows the relationship between these factors.
QUESTION:
What COL do you recommend with GSC bullets?
ANSWER:
There
is no COL recommendation for reloading your own cartridges. The rifle will
determine what COL works best with the combination of rifle and components that
you have chosen. As long as the cartridges fit the magazine of the rifle
and also the chamber of the rifle, the most important thing is to find the COL
that gives the best accuracy. See the the Load Data page and the
guidelines given under 'Procedure'.
COL tables are published as a guideline for manufacturers of rifles and cartridges so that rifle magazines are not shorter than the specification and cartridges are not longer. This ensures that all cartridges manufactured will fit all magazines that are manufactured.
See the Load Guidelines for HV bullets for more detailed information.
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GS Custom Bullets, situated in Port Elizabeth on the East Coast of South Africa, manufactures solid copper, turned, monolithic bullets for hunting and sport shooting. These bullets are used by hunters on several continents, hunting from the smallest of antelope to the largest of dangerous game, using the smooth HP bullet, as well as the more popular HV, FN and SP bullets with the patented drive band concept. GSC bullets are configured for the highest possible ballistic coefficients. SP bullets are mainly used for sport shooting. All GS Custom Bullets are coated.