Here is some more, I repost this data somewhat frequently because it's completely trounces the anecdotal comparisons that are typical of caliber arguments. It's kind of like the engine analogy when people argue engines....there's simply no replacement for displacement and that has proven time and again at the track regardless of technical arguments for or against. In the end, you just have to use it and see how it pans out.This is some awesome data! Thanks for providing it!
Keep in mind I don't generally agree with the mindset that "well if the AR platform allowed a longer case like 6.8x47mm" yada yada yada it would be x amount better but we'll have to settle for it as is....those arguments that talk about further increasing velocity via a larger case are moving too close to a full powered cartridge like 7.62x51...at some point it just becomes a slightly underpowered .308 with all of the draw backs of a full powered cartridge....why not just use .308 then?
Keeping muzzle energy in the 1600 to 1800 ft-lbs (depending on load, SAAMI spec, Handloads or NATO equivalent) range for 110 to 120gr keeps the ammunition weight low, capacity high and recoil low all of which are endearing qualities of the original 5.56 cartridge we don't want to move too far away from, while simultaneously addressing it's weaknesses.
However unlike 5.56, 6.8 SPC offers significantly increased single shot terminal performance and intermediate barrier penetration which are the weaknesses of 5.56, a somewhat marginal performer for medium sized game and human enemy combatants. 5.56 is lethal, but does not provide optimal incapacitation in a a variety of situations because well....there is just no replacement for displacement!
Weather by happenstance or not, keeping it to a small frame AR platform has basically created a modern American take on the 7.62x39mm concept. Unlike 7.62x39mm however, 6.8 SPC provides decent mid-range performance where 7.62x39mm tends to really start to peter out past 300 yards and is more optimal at close range, but is quite devastating at close range with modern fragmentation or expanding loads, ask hog hunters running that cartridge. It's more or less a 54R Short, kind of like 6.8 SPC is akin to a .270 Short.
Even the SAAMI spec commercial loadings offer good performance relatively, typically in the low to mid 1600 ft-lbs muzzle energy range out of a 16" barrel which is right on par with 7.62x39mm for close range applications while basically matching the trajectory of 5.56 77gr IMI Razor Core when also fired from a 16" barrel. I chronoed IMI 77gr Razor Core 5.56 in my 16" Daniels barreled 5.56 upper at 2586 fps average on the same day I chronoed 110gr Hornady OTM in my 16" Daniels barreled 6.8 upper...so it is what it is and that's what it's producing the real world (5.56 is particularly sensitive to barrel length, especially with heavy loads).
With 110gr Hornady OTM factory (aka American Gunner line, now discontinued, but using the original 110gr OTM bullet), I get 2584 fps average. Both Daniels Defense barrels are chrome lined, hammer forged, mid-length. Same chrono, same day one hour apart on the same lower. The 5.56 barrel is 1:7 twist 6R, the 6.8 barrel is 1:11 5R. Both even run the same muzzle device, an AFAB on the 5.56 upper and EFAB (7.62 version) on the 6.8 upper. Note the efab has slightly better flash suppression due to divergent nozzles, but from a back pressure standpoint, identical, similar design overall.
Both loads (77gr Razor Core and 110gr OTM) are MOA or just below MOA (I only have 6x mag LVPO, so better magnification I could probably squeeze a bit more out of both like a 15x Nightforce for example). Run of the mill 110gr 6.8 loads only running SAAMI spec pressure offer significant overmatch to even the best 5.56 loads without question. At close range, they are in two different leagues and barrier blind performance (for any tactical applications), is vastly superior with 6.8 as well.
The only thing I'd change about 6.8 is wanting factory NATO spec loadings (higher chamber pressures) to maximize performance a little more, but even as is, it's still quite superior, more is NOT always better in practice either, more muzzle energy = more recoil = slower follow up shot split times. For hunting or long range use, hot loads may be more beneficial, but for general purpose, I think SAAMI spec is quite optimal and extends component life. There is ALWAYS a trade off, so the question becomes what is the best balance for the application?
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