Comments by "Titanium Rain" (@ChucksSEADnDEAD) on "Task & Purpose"
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@chef7734 "The 6.8 spc has as much energy at 250 meters as the m855 has at the muzzle" - not true. M885 at the muzzle from a 14.5" is roughly 1600 J. A 110gr 6.8 SPC will have around 1300-1400 J at 200 meters. I don't see the energy climbing another 200 joule in the next 50 meters.
"You gain 40 to 50% kenetic energy at 300 meters and in and 35%greater out to 600 meters" - energy isn't everything. You need to put that energy into tissue. We know that with two bullets travelling at the same velocity, the lighter one tumbles better. We all know that with two bullets with the same mass, the faster one tumbles better. 5.56 is both faster (by about 100 ft/s) at 300 meters and lighter. More energy on a round that is more likely to icepick through and not put that energy on tissue means very little. Remember, you're gonna be using FMJ rounds which depend on the tumbling to transfer energy, not hollow points. With hollow points, by all means pick 6.8 SPC.
If the round weighs more, you're carrying less for the same weight. If the recoil is higher and bullet slower, marksmanship goes down because it becomes harder to guesstimate bullet travel time and bullet drop at unknown distances and once you pull the trigger you're gonna be slower to line up a second shot. You're gonna be carrying less firepower into battle, you're gonna be more likely to miss, and even if you hit you're less likely to actually put the target down. I think you're getting a bad deal with 6.8 SPC because of sheer physics alone. You can simply carry the same amount of ammo and add a bunch of weight to the rifle to bring recoil to 5.56 levels, but you're punishing your back for a caliber that's not going to do much for you and is gonna have worse trajectory anyway.
"You have a larger round that has more powder pushing it in the same magwell as the 5.56." - the larger bullet also takes up more case space. If I go by Nosler load data a 223 Rem case (for some reason 5.56 NATO doesn't have 62gr load data on their website) loaded with a 62gr bullet has a 27.6 gr H2O capacity. A 6.8 SPC loaded with a 110gr bullet has a 27.5 gr H2O capacity. Again through Nosler's website a 69gr loaded in a 5.56 case has 27.5 gr H2O capacity so I rest my case, the round itself is indeed larger but because you need to stick a bigger bullet in it and still respect the OAL of the AR's magwell and magazine dimensions... you're gonna have to push the bullet deeper into the case and lose powder capacity.
If you want more powder, you need either a lighter bullet (which is also shorter which gives it lower ballistic efficiency - an 85gr will have around 1040 J at 200 yards versus 5.56 62gr's 990 J - you're virtually negating the energy difference at this point) or neck it down. You're either back to 5.56 territory or trying to recreate 6mm SAW.
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