As discussed previously, while the 6.8 mm has repeatedly demonstrated outstanding terminal performance in JSWB-IPT testing, FBI BRF testing, USMC testing, and the recent CTTSO/TSWG MURG Congressional demonstration, keep in mind that the 6.8 mm design is a compromise that does not maximize assault rifle terminal performance, as it is constrained by the requirement to fit and function in the 5.56 mm M4/M16 magazine. The 6.5 mm Grendel is inhibited by this same limitation.
Primary focus during SPC cartridge design was to offer improved terminal performance, accuracy and flight characteristics from CQB range out to 500 meters from the M4 type platform compared to all existing 5.56 mm loads. The SPC was required to be easily retrofitting to current SOF 5.56 mm rifles (HK416, Mk18, M4, Mk12, M16) and be adaptable to proposed future systems (SCAR-L/Mk16, XM-8). The 6.8 mm SPC easily meets these criteria and has proven extremely reliable and durable in extensive functional testing.
Below is a 6.8 mm Horn 115 gr OTM shot fired from a 12" barrel into a bare gel block at 100m. MV = 2466 f/s, Impact Vel = 2263 f/s. Pen = 13.5", NL = 1", Max TC = 4.5" diam at 4.5" depth, extending from 1 to 9". RW = 85.6 gr.
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If freed from the M4/M16 platform imposed design compromises that limit both the 6.5 mm Grendel and 6.8 mm SPC, an "idealized" combat rifle cartridge, can be explored. As noted, virtually every wound ballistic test in the last 100 years points to a 6.5-7mm cartridge as offering the ideal combat performance--be it the 1920's era .276 Pederson, the post WWII .270 & .280 British cartridges, or the newer SPC program.
While at USAMU, Cris Murray, one of the co-designers of the 6.8 mm SPC simultaneously developed an "ideal" combat rifle cartridge, with none of the M4/M16 platform imposed design compromises that limit both the 6.5 mm Grendel and 6.8 mm SPC. Murray's 7 x 46 mm, offers better range and terminal performance than 6.5 mm Grendel, 6.8 mm SPC, or any other common assault rifle cartridges, including 5.45 x 39 mm, 5.56 x 45 mm and 7.62 x 39 mm. Since the 7 x 46 mm is based on the proven Czech military 7.62 x 45 mm cartridge, it has an established record feeding and functioning in both magazine and belt-fed full-auto fire. Likewise, recoil appears manageable and weapons remain controllable in FA fire, just as with the Czech cartridge. Like the 6.8 mm, the 7 x 46 mm is optimized for shorter barrels and larger magazines than the heavier, bulkier, and harsher recoiling 7.62 x 51 mm/.308 cartridge. In addition to Murray's 7 x 46 mm, the older FN 7 mm's (7 x 44 mm, 7 x 47 mm, and 7 x 49 mm), as well as the newer 6.5 mm Creedmore are worthy of consideration. For that matter, revisiting the British .270/.280 wouldn't be a bad idea. Keep in mind that the OAL of these cartridges is a bit too long to fit into the M4/M16 or other 5.56 mm size weapons/magazines
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As a result, these cartridges should ideally be used in all new rifle designs optimized for their characteristics.
Below is a 7 x 46 mm shot from a 16" barrel, using the 120 gr Hornady OTM fired into a bare gel block at 100 meters. MV = 2801 f/s, Impact Vel = 2529 f/s. Pen = 15.5", NL = 1.5", Max TC = 6" diam at 5" depth, extending from 1.5 to 9". RW = 84.2 gr.
Hard armor of NIJ Level III/SAPI protective levels will stop ALL standard military OTM and FMJ, including mild steel core ammo, such as 5.45x39 mm M74 FMJ, 5.56 mm M193 and M855 FMJ along with Mk262 OTM, 7.62x39mm M43 FMJ, 7.62 x 51 mm M80 FMJ and M118LR OTM, 7.62 x 54 mm Type L FMJ, and .30-06 M2 FMJ. This same Level III armor can be easily be penetrated by any of the same calibers listed above when using common military AP ammo.
If you want to stop most rifle AP ammo such as the .30-06 M2 AP "black-tip, all you need to do is use NIJ Level IV/eSAPI type hard armor. Yet even that can be penetrated using the right ammunition... Penetrating armor is not about caliber--it is about bullet construction.
7.62x33mm, 5.56x45mm, 6.8x43mm, 7.62x39mm, 7.62x45mm, 7x46mm, 6.5x47mm, 7.62x51mm, 7.62x63mm
As I have publicly stated previously, we have three choices:
-- Adopt improved barrier blind 5.56 mm ammunition for our current weapons.
-- Adopt an improved intermediate assault rifle caliber, like 6.5G or 6.8 SPC, that can be retrofitted to our current and near term weapons.
-- Adopt a larger case capacity combat caliber, like 7 x 46 mm or an enhanced 7.62 x 51 mm load, along with a new modern rifle system.
