How to choose a BC for your barrel?

1. Know the rifling pitch (twist) of the barrel.
2. For your Twist, choose the heaviest bullet possible (for our tasks: Long Range) with a gyroscopic stability factor FGS – (Sg) not lower than 1.5 in the MOST EXCELLENT conditions (according to Brian Litz’s guide).
3. Among them, find a bullet with a minimum form factor (i7).

IMPORTANT!
– Sierra Match King HPBT bullet – used in BC GGG
– GGG 175 gr – is a complete analogue of NATO – M118 LR with a difference in muzzle velocity +10 m/s (175 gr is also a stunner) – for ballistic Calculators – important!!!

Matching a bullet to your barrel

Brian Litz’s rationale:
“It’s quite common to judge a bullet’s potential ballistics by its ballistic coefficient, and rightly so, because BC is a very important parameter. However, you can’t easily determine a bullet’s aerodynamic drag by BC alone, because BC is a combination of the bullet’s lateral load and its form factor.

The lower the aerodynamic drag of a bullet, with a given lateral load, the better it will maintain its velocity. In other words, a bullet with low aerodynamic drag (as indicated by a low form factor) will more efficiently use the energy (velocity) imparted to it by the rifle.

I move on to an important conclusion: when choosing a bullet from the point of view of external ballistic characteristics, the first step is to choose the caliber and the corresponding weight range (light, medium or heavy) that you are interested in, and then look for a bullet with a low form factor in that range.

When selecting a rifling pitch for a particular bullet, it is advisable to strive for a FGS (Sg) value
of at least 1.4. .the military uses a safety margin in the range from 0.5 to 1.0 (+ to a minimum value of 1) due to the extreme natural and combat operating conditions.

– Best conditions: Altitude: 1000 ft (305 m), 100% humidity, T air: 100 °F (37.7 °C), Vo: 3000 ft/sec (914 m/sec).
– Nominal condition: Altitude: 0 m, 50% humidity, T air: 59 °F (15 °C), Vo: 2800 ft/sec (853 m/sec).
– Limit conditions: Altitude: 0 m, 0% humidity, T air: 0 0F (- 17.7 °C), Vo:2600 ft/sec (792 m/sec).

Glory to Ukraine!