6mm GT Load Development: A Practical Guide

The 6 GT was purpose-built for exactly one job — run high-BC 6mm bullets fast enough to compete, feed reliably from an AICS magazine, and do it on less powder than a 6 Creedmoor. It landed in 2019 and PRS shooters took to it quickly. Here is how to develop a load for one.

Why the 6 GT caught on so fast

George Gardner of GA Precision and Tom Jaczko of Alpha Munitions designed the 6 GT around a practical problem rather than a ballistic one: the 6mm cartridges winning matches were either hard on barrels, awkward to feed from a detachable magazine, or both. The 6 GT’s case body and shoulder were shaped to feed cleanly, and its capacity was set to push 105–110 grain bullets to competitive speed without running the case at its limit.

The practical result is a cartridge that gives up very little to a 6 Creedmoor on paper while burning less powder, producing less heat, and generally lasting longer in a barrel. It is also mild enough to spot your own impacts, which is the whole game in a timed stage.

What shooters reach for (starting points)

• Powder: Varget and Alliant Reloder 15 are the traditional starting points for the 105–110 grain range, with Alliant AR-Comp, Vihtavuori N150 and N550, Hodgdon H4350, and Shooters World Precision all in common use. The 6 GT is not a picky case — several powders will get you into a workable window, which is exactly why testing your own barrel matters more than copying a recipe.
• Bullets: the 105 Berger Hybrid, 109 Berger Long Range Hybrid Target, 110 Sierra MatchKing, and Hornady 108 ELD-M are the mainstays. These are long, high-BC projectiles — check that your throat and twist actually suit the one you pick before you buy a case of them.
• Brass: Alpha Munitions made the first 6 GT brass and it remains the reference; Lapua and Hornady both produce it now as well. Small primer pockets are standard, which suits the pressures this case runs.
• Primers: small rifle — CCI 450, CCI BR-4, and Federal 205M are the usual picks. Match the primer to the powder you settle on and keep it constant through your testing.

The process — same as any cartridge, 6 GT flavored

1. Pick your components and look up published minimum and maximum charges for your exact bullet and powder pair. The 6 GT’s published data is younger than a Creedmoor’s — Hodgdon, Alpha Munitions, and the bullet makers are the references worth trusting.
2. Run a powder ladder. Load a spread of charges across the safe range and chronograph every one. You are looking for the velocity flat-spot — the stretch of charge weights where adding powder barely moves speed. That is the window that tolerates a cold morning and a warm afternoon. How to read a powder ladder →
3. Run a seating-depth test at the charge you confirmed. Long-ogive 6mm match bullets respond to jump, and the 6 GT is no exception. Let your own groups make that call rather than a forum thread. How to run a seating-depth test →
4. Confirm at distance. A 6 GT load that looks identical to another at 100 yards will separate at 600 — velocity consistency shows up as vertical, and vertical only becomes visible with some range in front of it.

Let the data pick your best load

The 6 GT has a short enough history that there is no decade of accumulated folklore to lean on — which is an advantage if you test properly. Import your chronograph data (Garmin Xero, LabRadar, MagnetoSpeed, Athlon) and your target groups, and Loadscope scores every charge and seating depth you shot on velocity flat-spot, velocity SD, mean radius and vertical spread, then names your best load and prints a pocket range card for it. How the scoring works →