Quote:
Originally Posted by Trivers
"Compared to the 6.8×43mm Special Purpose Cartridge, another round made to have increased stopping power over the 5.56 NATO, the 300 Blackout has different capabilities. The 300 BLK was designed with a specific shorter-range focus to have equal or more energy than the 7.62 Soviet and work reliably with suppressors. The earlier 6.8 SPC was simply designed to have more energy at all ranges than the 5.56 mm. It has a relatively small projectile with a high velocity that maintains performance at range. At 200 yd (183 m), the 300 BLK drops 2 in (51 mm) lower than the 6.8 SPC, while it drops 30 in (760 mm) lower at 500 yd (457 m). The 115 gr (7.5 g) 6.8 round has a higher muzzle energy of 1,694 ft·lb (2,297 J) due to its greater velocity, while the 125 gr (8.1 g) 300 BLK round has a muzzle energy of 1,360 ft·lb (1,840 J). Both rounds were made to be used in an easily converted AR-15 platform. The 6.8 SPC has a more difficult conversion because it was designed around the .30 Remington cartridge, requiring a different bolt and decreasing standard magazine capacity. The 300 BLK was made specifically for ease of conversion, so the standard bolt will work and a magazine can be used to its full capacity, so the only change needed is the barrel.[12]
Extreme care should be taken with 300 BLK ammo, as with certain bullet profiles, the round may chamber in a standard .223 or 5.56 AR platform with disastrous results and possible injuries."
From Wiki.....
So all one has to do is change the barrel from 223 to 300 BLK before using?
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Yep. So basically you have two different yet complete uppers, one for the 5.56 and one for the 300 blk. All you have to then do is swap the uppers out with the one lower (super easy to do). Same magazine will work for the 5.56 and the 300 blk.
Now, it is a bit costly to have two complete uppers but the swap is so damn easy it's almost too good to be true. I've priced out building a 300 blk upper and it costs
up to $1400. The key is getting a good barrel. You may be able to do it for around $1000.