NEW .300 AAC BLACKOUT CARTRIDGE
this is a big minus. Moreover, there are engineering downsides to adapting the M16 bolt for the 6.8 and 7.62X39mm cartridges. Stoner originally designed his AR15 around the .222 Remington and its small 0.378” dia. case-head; the cartridge grew into the larger capacity 223 version but retained the original case’s diameters. The AR / M16 bolt can be opened out to accept the 6.8’s 0.422” and the 7.62mm M43’s 0.447” case-heads, but it leaves precious little metal at the base of the locking lugs to support them. 7.62X39mm/22PPC AR bolts used by civilian Service Rifle competitors are known to have a finite life and are more likely to crack or fail in use than in the original 223 Rem form.
The ideal alternative calibre M16/M4 cartridge meets the following criterion:
• Allows use of standard bolts and magazines. Conversion to be limited to new barrel.
• Provides 7.62X39mm M43 ball external ballistics in supersonic versions. (123gn FMC flat-base bullet at 2,350 fps MV from a 20” barrel – SAAMI spec.)
• Offers a heavy bullet subsonic version for short-barrel sound moderated special forces carbines and SMGs.
• Optimised for efficient muzzle flash suppressor operation.
• Operates standard M16/M4 actions reliably in both semi and full-auto operation.
• Provides good barrier penetration (buildings, vehicle bodies, personal armour etc).
Whisper it Quietly! Enter the 300 AAC Blackout earlier this year,
developed by the Advanced Armaments Corporation with manufacturing / technical support by Remington Arms’ ammunition division. The ‘Blackout’ has been registered with SAAMI and given an official abbreviation as the 300 BLK. Basically it’s a cut- down 222/223 Remington case (43/45mm reduced to
35mm) reformed with a short larger calibre neck to hold a standard 30 Cal (0.308” dia.) bullet.
There is only a vestigial shoulder when you do this to such a skinny case but it’s still adequate for headspacing in the rifle chamber in the normal way. The military standard ball round utilises either a 115gn UMC type (FMJ) or 125gn OTM (Open Tip Match) design, both flat-based, in the cartridge’s supersonic loadings. For sound-moderated carbines, it uses a 220gn OTM bullet at just over 1000 fps MV.
Hang on a second! Those who know their cartridges will recognise this as the .300 Whisper wildcat developed by J.D. Jones of SSK Industries around 20 years ago and popular amongst US handgun hunters in weapons like the Thompson/Center Encore. This was based on a necked-up 221 Remington Fireball case which in turn is a truncated 222 Rem.
This is exactly what the new 300 BLK is but regularized and specified in the SAAMI database, also with loadings sorted out that will feed reliably through a rebarrelled AR15/M16 and operate the gas-powered action reliably without overstressing the moving parts, including very short barrel carbine formats – as little as nine inches.
Whilst the Whisper user can adopt any bullet/COAL that his single-shot pistol’s barrel has been throated for and any load that both pushes the bullet clear of the muzzle or without creating excessive chamber pressures, the BLK must run at around 2.25” COAL, 2.26” maximum and be tuned for gas-operated selective-fire assault rifle operation. That’s what AAC has done and sold the idea to Remington and the US military.
The nominal ballistics are: 9” barrel: 16” barrel: 9” barrel: 16” barrel: 9” barrel
115gn UMC 2,120 fps MV 1,136 ft/lb ME 115gn UMC 2,295 fps MV 1,344 ft/lb ME 125gn OTM 2,030 fps MV 1,143 ft/lb ME 125gn OTM 2,215 fps MV 1,360 ft/lb ME 220gn OTM 1,010 fps MV 498 ft/lb ME
Effective ranges are quoted as 500 metres for the supersonic ball versions and 200 metres for the 220gn heavy bullet moderated weapon type. The benchmark for the latter is much lower performance subsonic 200gn 9mm Para pistol cartridges currently used in MP-5 type carbines.
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