|In debates over what would be an optimal round for infantry forces, it is often brought up that the optimum is thought to lie somewhere between 6mm and 7mm calibers. Perhaps the most often mentioned round is the 6.8mm Remington SPC. The round, however, is 6.8 x 43mm, so its trajectory would likely be worse than that of the 5.56mm. This might be compensated for by its other benefits, but would it not make more sense to use longer rounds, in order to achieve better trajectories? For example, we could take the length of the 7.62x51mm NATO round and create a 6.3x51mm round. This would have the same mass/volume of projectile to mass/volume of propellant ratio as the 5.56x45mm round (assuming round proportions would stay the same, which they well might not [I am not an expert], but the principle holds regardless), so it would have a very flat trajectory, but would lie in the 6mm-7mm caliber sweet spot and still be significantly lighter than the 7.62x51mm round.
What do you think?