Three Letters Re: .300 AAC Blackout Uppers for AR-15s

Jim.
An additional point or two on the viability of the 300BLK. While I agree that the primary concern should be to have your standard calibers covered, the 300BLK has the additional advantages. Because it is made from 223/5.56 brass, and uses any 30 caliber bullet, it will be easily reloaded in a SHTF situation. Another advantage is the ability to use the round suppressed (using subsonic rounds)with as close to “Hollywood” results as you will get. Although the advantages of using silenced weapons in a SHTF situation has been touched on in this forum I believe the subject could use more emphasis. Thank You James, – Rick .S

Jim,
Regarding the .300 AAC Blackout (“300blk”) cartridge for the AR-15 rifles, I would like to add some favorable comments about the new caliber. But first, I really don’t like new calibers (for AR-15/M4 variants) at all. I never jumped on any bandwagon for a new AR-15 caliber (6.8, 6.5, 5.45, etc) over the last 15 years and have and still do preach the “common caliber” mantra… but now I have jumped into the “new  caliber” crowd with the .300 AAC blackout. Here is why:

I want the best of many worlds. I have for years wanted an AR-15 that will put down the threat effectively, punch through medium barriers, but also be super sneaky quiet like an MP5SD. In fact I have often lamented the fact that I can’t cross the MP5SD (quiet) with an AR-15 (ergonomics, low recoil, accuracy) that punches through barriers like an AK-47. Laugh if you will but I want all in one! With good ammo the 5.56×45 does just fine or even fantastic at putting down threats, but definitely lacks in barrier penetration and really can’t be considered to be anything but loud, even with a suppressor. This all changes with the 300blk.

The 300blk cartridge is gaining significant steam down south (among other places and including some special units) where hog hunters need decisive effects on target like Paul S. said. It basically gives you a 7.62×39 ballistic effect (.30 caliber, heavier projectile for barriers, etc) but in a package that allows you to have both the MP5SD and 7.62 advantages. With the swap of a magazine (lighter grain supersonic loads in one, heavier subsonic loads in the other) and rack of the charging handle, you do indeed go from a 7.62×39 equivalent “full power” carbine/assault rife round to a super quiet round comparable to the long standing standard in suppression, the MP5SD, presuming of course you do have the suppressor attached. The advantages to having both options at your fingertips within seconds without carrying a secondary long-gun should be obvious.

Another great feature of the 300 AAC Blackout cartridge is that it was optimized in both supersonic and subsonic loadings to get maximum velocity out of only a 9” barrel! With the ever-increasing popularity of SBRs (short-barreled rifles, requiring a $200 NFA tax stamp through the BATF), and the handiness and lighter weight of short rifles, this is in my opinion, a very significant breakthrough, as the biggest disadvantage of SBRs is usually the significant drop in velocity (and associated drop off in terminal effects on target), which is NOT the case with with the 300blk. It has its full potential out of just the 9” barrel! Quality supersonic cartridges are capable of sub-moa, while subsonic cartridges are hovering consistently around 2 moa, but custom subsonic loads are doing sub moa. With ammo standardized by Remington and nearly everyone making ammo for it now, it seems to be catching on with far deeper roots than the other recent “fad” calibers for AR-15s. Another great thing about the caliber is the ability to use the AAC 762SDN6 (or similar .30 caliber suppressor) suppressor on many calibers. I tried mine on my 5.56 SBR and it sounded the same or slightly quieter than my dedicated 5.56 suppressor did while only being about 3/4” longer and about two ounces heavier than my AAC M42000 (5.56 suppressor).

Keeping in mind that the 300blk is very rare in comparison to “common calibers” it would likely be a good idea to keep at a minimum a 5.56 barrel (and gas block and gas tube for the 5.56 barrel) on hand in case your supply of 300blk dries up in a TEOTWAWKI situation. Of course a complete 5.56 upper would be easier to swap but would cost more. I would like to add to Paul S.’s comments that the 300blk uses the same bolt, carrier, upper, and magazines, like he said, but unlike some other AR-15 variant calibers, the 300blk does not just use AR-15 magazines such as the Magpul PMAG in a tolerable manner, but in a perfectly reliability manner, just as good as the 5.56 cartridges due to the same cartridge base, width, taper and OAL.

Downsides? I’ve already disclaimed that you should have your “common calibers” at hand. That aside, I could see someone claim that 30 rounds of 125 grain ammo weighs more than 30 rounds of 55-77 grain ammo. True, but for the advantages I think it well worth it. Also, the 300blk does have more of a “lob” ballistically than the 5.56 which somewhat limits its practical range to around 400 meters (compared with the generally accepted practical range of the M4 at 500-600 meters — though of course Travis Haley was ringing steel at 600 meters with ease with his) before you really really have to know the range and hold-overs perfectly. But in my opinion a carbine isn’t really very useful past that in most cases anyhow.

All in all, as long as you already have stocked your “common calibers” the .300 AAC blackout AR-15 uppers have just about every advantage and no noticeable disadvantages and when mated with a quality suppressor, provide an operational flexibility and force multiplier that should not be ignored. – PPPP

Dear Editor:
Just one potential problem must be noted for those who wish to swap uppers back and forth between 5.56/.223 to .300 Blackout: If you forget, or get distracted, it is possible to put a magazine full of .300 AAC Blackout ammo into your AR with the 5.56/.223 upper installed. When you hit the bolt catch, the first round of Blackout will be completely chambered in the 5.56 upper. This can happen because the bullet will be forced deeper into the Blackout brass. If you pull the trigger, the chambered .300 Blackout round will ignite, and the bolt will explode, and most likely split the carrier and the upper receiver as well. I have seen this happen. You have been warned! – CTBill