Owner's Manual

MAGAZINES
AAC 300 BLACKOUT ammo can feed from standard USGI or Magpul P-Mags. A magazine with the standard MIL-STD
17-7 stainless spring may be stored fully loaded with 30 rounds indenitely. Note that Chrome Silicon springs will
not resist taking a set better than MIL-STD 17-7 magazine springs regardless of how they have been marketed.
SOUND SUPPRESSORS
The recommended sound suppressor is the AAC 762-SDN-6. This has been tested to provide a good balance
between sound level, weight, accuracy, and reliable function. Suppressed SPL with AAC subsonic ammunition is
approximately 126 dB both using MIL-STD measurements and at the shooter’s ear.
AMMUNITION
There are two special considerations for the AAC upper - gas port pressure, and reliable feeding from a magazine.
300 AAC BLACKOUT (300 BLK) ammo from Advanced Armament Corp. is designed for reliable function in self-loading
rearms.
HANDLOADING
If you load your own ammo, pay special attention to all of the normal safety practices. Recommended powders for
most supersonic loads are Hodgdon H110 and Lil’Gun.
For subsonic, there are special requirements and nearly all published loads are non-optimal for the 300 BLK upper.
Many existing loads were developed for Thompson Center® single-shot pistols, or for ARs by people not aware of
the magazine limitations. These loads pay no attention to automatic rie function and should not be used. Look for
a load which results in a cyclic rate of 700 rpm or more. AA1680 is recommended because its bulk density matches
the case capacity and it will generate enough gas pressure to cycle the weapon.
Suggested subsonic load:
Existing AR magazines have a rib which normally contacts the 5.56mm case-neck. With 300 BLK ammo, the
contact is on the bullet. Because the bullet is a larger diameter, the rib will push the cartridges out of alignment, and
can lead to binding potentially resulting in Failures to Feed. For this reason, it is important to load ammunition so that
the contact point with the magazine rib is on the bullet ogive in an area of about 0.250 inch diameter. Here are some
suggested OAL for popular bullets:
USER MODIFICATIONS
The gas-port diameter was selected after thousands of rounds of function testing and high-speed video analysis.
We do not recommend you enlarge your gas-port to aid subsonic function because then supersonic ammunition
will hyper-cycle the upper which will reduce the reliability and part life durability of the system. AAC has developed
subsonic and supersonic ammo that both function reliably (with and without an AAC 762-SDN-6 sound suppressor)
without the need for an adjustable gas block.
If your subsonic ammunition is not cycling the upper, consider using a powder which generates more gas-port
pressure. AA1680 seems ideal for this use.
BARREL LIFE
The barrel of the AAC BLACKOUT upper is made from 4150 CMV and specially processed to have up to 60% more life
than a chrome-lined barrel and without the potential loss in accuracy from uneven coating. This processing also
results in extreme corrosion resistance.
ACTION SPRING/BUFFER
Use either the standard USGI M4 or the HK 416 spring. For buffers, select a 4.6 oz (130 gm) H2 or an HK-416 buffer-
though a 5.5 oz (155 gm) H3 buffer may be a good choice if you don’t intend to shoot subsonic without a sound
suppressor or typically shoot supersonic ammo. Do not use a solid 9mm buffer as it may cause bolt bounce.
EXTRACTOR SPRINGS
We have 5.56mm test data for the Bushmaster ‘4 coil’ extractor spring with a blue insert and an o-ring. Four uppers
completed a 12,000 round test with no extractor spring related failures. Two uppers completed an 18,000 round test
with no extractor spring related failures.
We do not recommend using extra-power extractor springs because they are under higher stress and will likely
break sooner. The included o-ring adds the desired extra extractor force without requiring a spring which would
have more force and hence more stress. Also, extra-power springs, when combined with an o-ring, may make the
extractor harder to snap over the case rim and may lead to function problems. If you do use such a spring, please
don’t use an o-ring and change the spring every 1500 rounds for mission-critical use.
Note that, again per our spring discussion, Chrome Silicon springs do not resist taking a set better than ASTM A228
certied music wire when used at temperatures below 250 degrees F.
CLEANING/LUBE
Recent US Army testing has shown that ARs work best with heavy lubrication. This is even true when used in a
sandy environment. While many have said to avoid heavy lube to keep sand from sticking to the parts, this has been
proven to be incorrect. Lube keeps the sand in suspension and allows the gun to function. Even if you do not have
time to clean the weapon, add lube (such as CLP) every 300-500 rounds. Shooting with a suppressor requires more
frequent lubrication.
• R-P 300 AAC BLACKOUT brass
• Remington 7.5 primers
• 11.2 grains of AA 1680 powder
• Sierra 220 MK loaded to 2.089 OAL (this length is optimal for reliable feeding
from USGI magazines)
• Chamber pressure 21,100 psi.
• Hornady 110 V-Max, OAL: 2.000
• 110 TSX, 2.015 OAL
• Sierra 155 Palma, 2.150 OAL
• Sierra 220, 2.089 OAL
• Lapua B416 200 grain, 1.960 OAL
• Hornady 150 FMJ-BT 3037, 2.065 OAL
• Nosler Ballistic Tip 125 grain, OAL: 2.085
• Remington AccuTip 125 grain, OAL: 2.085
• Hornady 130 SP #3020, OAL: 2.010
• Sierra H2120 125 ProHunter, OAL: 1.950
• Speer TNT 125 1986, OAL: 2.010