With what seating depth can load development be started and to what depth can GSC drive band bullets be seated?

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 (the first drive band) must never be inside the case neck.  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, to get the COL.

Please note that the bullets in the illustration below have seven drivebands.  The first drive band is cut onto the rear of the ogive and has a different shape to those drive bands that follow.  Depending on the cartridge and the length of the shaft, a GSC drive band bullet can have 4 to 7 drive bands.

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?

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.

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?

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.

What COL do you recommend with GSC bullets and is 'jump' to the rifling of the barrel important?

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.

There is a rule about GSC drive band bullets that is cast in concrete and that rule says:  There are no rules!

Do the tests at these pages and, if the rifle passes, do the third test below.

Test #1

Test #2

Test #3:  A GSC drive band bullet centers itself in the freebore, To achieve accuracy, it is not required to have ammunition that is as close to the rifling as possible.  Do the test whereby you load five or ten rounds and measure the runout of the bullets in the casing.  Cycle the reloads through the action of the rifle and measure them again. The ammunition has less runout than what they were before.

 See the Load Guidelines for HV bullets for more information.