I’ve written quite a lot about the ballistics one of the first Western competitors to 5.56mm in the new millenium previously, and you can read that by following the link here. The 6.8x43mm Remington SPC was developed in the early 2000s by MSG Steve Holland and civilian US Army Marksmanship Unit gunsmith Cris Murray as a second iteration for the Mk. 12 SPR precision upper receiver for the AR-15. The 6.8 SPC was never adopted by a Western fighting force, but it subsequently became a popular civilian hunting cartridge, and it still features prominently in discussions about next generation military calibers, so let’s take a look at the ballistics of two popular 6.8 SPC loads:
The XM68GD 90 grain soft point round is one of the lightest 6.8mm SPC rounds there is, at about 15.9 grams (245 grains) per. The 110 grain Hornady load weighs about 17.6 grams (272 grains) in contrast, while the heaviest factory load, the 120gr Hornady SST, weighs about 18.2 grams (281 grains).
Note: All ballistic calculations are done with JBM’s Trajectory calculator, using the ballistic coefficient appropriate to the projectile being modeled, and assuming an AR-15 as a firing platform. Also, keep in mind that there is no single true velocity for a given round; velocity can vary due to a large number of factors, including ambient temperature and chamber dimensions. Instead, I try to use nominal velocity figures that are representative of the capability of the round in question. The velocity figures I use here are educated guesses for the barrel lengths used, based on velocity figures collated from here, here, and here.