Forming 300 Blackout brass

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Forming 300 Blackout brass

Category : Reloading

Forming .300 Blackout Brass

300 AAC Blackout, SAAMI short name 300 BLK, also known as 7.62×35mm is a rifle cartridge developed in the United States by Advanced Armament Corporation (AAC) for use in the M4 carbine. Its purpose is to achieve ballistics similar to the 7.62×39mm Soviet cartridge in an AR-15 while using standard AR-15 magazines at their normal capacity, and retaining the standard 5.56/223 Remington AR15 Bolt Carrier Group (BCG). 300 AAC BLACKOUT was approved by SAAMI on January 17, 2011. In theory, conversion from .223/5.56 to .300 Blackout requires only a barrel change. In places where a suppressor is legal, the 300 BLK can be loaded to subsonic velocities with heavier (190+gr) spitzer-style bullets, which are much more efficient than the pistol bullets normally used in these applications.

Forward by Keith Byrnes

I would like to start off by saying that I never had any plans to get involved with long guns, or forming brass, or swaging bullets at all. It all started out with my friendship with orville Deutchman. He is the person responsible for all of the rifle stuff that I do, including brass forming and bullet swaging addiction. I call him my “dealer”, a term of endearment meaning mentor. We started out using Orville’s set of .224 swaging tools, which converts used .22 LR brass cases into donor jackets for making 55 grain bullets for 223 Remington. So, hence, I bought an AR15 in 223 Remington. Then, Orville brings out a 300 Blackout AR, and mentions that we need to swage .30 cal 150 grain bullets from 5.7 X 28 FN donor cases. So, I end up building a 300 AAC Blackout. The cases for 300 AAC Blackout are hard to come by at the range. And, being on a budget, purchasing the quantities that we needed was cost prohibitive. So, Orville suggests we can make 300 AAC Blackout cases out of 223 Remington brass. Now for the rest of the Story.

Beginning Plans

After doing some research, we settled on 5.56 Lake City brass, primarily due to the conformity of the brass. It has the proper dimensions, especially regarding the wall thickness. When cut down, and reformed, the necks would be the perfect thickness, .0015”. Commercial brass varies in the thickness of the brass, and would give results from .012” to .0135, too thick”. The .0015” necks on the Lake City brass turned out to be very consistent, and eliminated any need to otherwise try to fix the brass.

We had to come up with a way to cut the brass down. And, it was important that the cut length was somewhat precise and consistent. We needed to leave a slightly longer length than was needed, about .002”, so that we could trim the brass to final length and deburr it. I had been swaging several sizes of pistol bullets, and had a set of pop through fixtures made for my Harbor Freight cut off saw. One of those fixtures was one which handled .223 Remington cases. We decided that Keith would handle the initial stages of the conversion from 5.56 Nato brass to 300 AAC Blackout.

The Steps

  1. Batch size is 3,000 pcs. Sort brass by head stamp, choosing only Lake City 5.56 Nato brass
  2. Brass is cleaned and polished. SS Pin tumbling for 2 hours, rinsed with fresh water, followed by drying in a Harbor Freight food dehydrator tray, on high for an hour. Polished in walnut shell, with NuFinish car polish and mineral spirits.
  3. A Dillon RL550b is set up with a case feeder, and brass is run through the Dillon, with only a Lee Universal Decapping Tool in station 1.
  4. The crimps in the primer pockets are then removed using a Dillon Super Swage 600.
  5. The cases are cut trimmed to 1.370”, using the pop through fixture in the Harbor Freight saw. We use a good quality saw blade :
    1. The P/N for the saw we are using from F&D is: 15397-J156
      The specs are: 15397-J156 Jewelers Slotting Saw
      Outside diameter:2″
      Thickness: .020″
      Hub diameter: 3/8″
      Teeth per inch: 24
      Teeth per blade: 152
    2. Or….
      Malco equivalent, JS202038000, same specs
    3. The blades cost under $10 each, and are much superior to the so-so quality blades from Harbor Freight. We have run over 10,000 cuts on one of the good blades, whereas the HF blades only last for 3-4,000 cuts. The burr from the cutting operation is almost non-existent with the quality blades.
  6. The cases go back into the case feeder for the Dillon 550, and get run through a Lee 300 AAC Blackout die set. The overall diameter dimensions are now right on the money. The neck is a little long, due to the planning in step 5.
  7. The cases are trimmed to final length using a Giraud Trimmer to the final 1.368” overall length. The Giraud trims and deburrs at the same time.
  8. The resultant cases are then run through a neck annealer, made by Annealeez. . The Annealeez machine was chosen because it was a lot less expensive than many of the other options.The proper amount of annealing is achieved by heating the neck to about 800° F for about 6 seconds, while ensuring that the body and case head do not exceed 425 ° F in the process – a process made extra difficult by the relative shortness of the 300 Blackout case. Annealing must be precise and consistent. The old “spin-the-case-on-a-welding-rod-in-a- BernzOmatic-flame-for-a-10-count” method won’t cut it.You can try skipping the annealing step, but if you have problems with inconsistent velocity, poor accuracy, and short case life, annealing may be the only fix. If the price of an automated annealer is too prohibitive, try to find another reloader to go in on it with you.
  9. The final product is again run through the crushed walnut shell vibratory system with the NuFinish polish and mineral spirits. That gives them a long lasting protection against humidity.

Keith and I are also producing our own 150 grain bullets for the 300 AAC Blackout cartridges. We’re using 5.7 X 28 FN cases as the donor jackets for these high quality, home made jacketed bullets. They will be the subject of another article. Stay tuned.

If you have any questions regarding the making of 300 Blackout brass from 5.56 NATO cases, feel free to Contact Orville at 386-753-8898.



Figure 5 – Prep steps from left-to-right: A 5.56 NATO parent case, trimmed , annealed, and sized/cleaned

Final thoughts

Many shooters buy a .300 Blackout upper to add versatility to their existing 5.56 AR-15. As stated earlier, one benefit is that you can use the same magazines with both calibers. Technically speaking, you can use the same bolt too, but it’s not a good idea to do so. There’s a saying about the AR-15: “New barrel, new bolt”. Because the bolt and barrel wear and break in together, you should always use a new bolt with any new AR-15 barrel, and not use a bolt with more than one barrel. If you’re going to get an “extra” 300 Blackout upper, get a new dedicated bolt or entire bolt/bolt carrier assembly to use with it.

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