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Converting a .223 Rem case into a 300 AAC Blackout round
November 5th, 2015 by RoundsReloaded

As a reloader I never, until recently, gave any attention to the 300 AAC Blackout round, mainly because I only reload calibers for which my firearms are chambered in.
As a reloading instructor, I had many people ask me about the 300 AAC Blackout round and, until now, I had always brushed it off as mass hysteria.

Things changed when I started building my own AR-15 rifle. I read something somewhere on the net that made me take a closer look at this round, in a nut shell this is what got my attention: You keep the same AR-15 lower, magazines; same bolt carrier group and same charging handle and only switch the upper and done! You got yourself a new rifle chambered in a 30 caliber round; what a cool idea!!!

Then, as a reloader, I started looking at what it was needed to convert a 223/5.56 NATO shell into a 300 AAC Blackout round and realized that it is easier than you might think, as I am about to show you here below.

If you already reload you already have many of the tools you need, what you will need additionally though are: a mini chop saw and a rig to hold the .223 shell in place while cutting it plus, of course, a set of 300 AAC Blackout dies.

Step 1: Sizing and depriming a 223/5/56 NATO case.

I started by sizing and depriming the shell casing, as I would do if I was preparing to reload another 223 round (Figure 01). At this time is a good idea to check the primer pockets and make sure to clean and deburr the primer crimp, if you are reloading military surplus rounds, they usually have a crimped primer.

Figure 01: .223 REM/5.56 NATO shell casing, sized and decapped

Figure 01: .223 REM/5.56 NATO shell casing, sized and decapped

 Step 2: Cutting the shell casing.

To accomplish this step I purchased an inexpensive mini chop saw with a 2″ blade (Figure 02). It seemed to be a tool made especially for this task. I also bought a jig specifically made to hold 223 cases firmly in position for cutting. It comes already made to accommodate the slight taper of the 223 round so the cut is perpendicular to the shell’s longitudinal axis. This eliminates excessive trimming later. One thing worth mentioning at this point is that the case holding jig was set on the base of the cutting tool by carefully measuring the location of the cut with a caliper and firmly tightening it into position. The mini chop saw and the holding jig are readily available online through various websites including Amazon.

Step 3: Measuring and trimming.

After cutting the case I measured it again to make sure the cut was accurate (Figure 03) and then I proceeded to trim the case (Figure 03) to its final new dimension as per SAAMI specs.

Figure 04: Measuring case after cutting

Figure 03: Measuring case after cutting

At this point I deburred the mouth of the case (Figure 04).

Deburring the case

Figure 04: Deburring the case

 

Step 4: Sizing and priming.

I run the case through the resizing die and I primed the case (Figures 05 & 06).

Sizing the case

Figure 05: Sizing the case

Priming the case

Figure 06: Priming the case

A 300 AAC Blackout case is now ready to load (Figures 07 & 08).

Figure 07: 300 AAC Blackout case

Figure 07: 300 AAC Blackout case

300 AAC Blackout case

Figure 08: 300 AAC Blackout case

 

From this step forward the process is the same as for any other round, that is, charge the case using reloading data found in any reloading manuals, sit the bullet, also selected by using data found in the reloading manuals and finally crimp the mouth of the cartridge.

I have not yet made it to the range to test the rounds I have made, therefore, as for performance the jury is still out.

I will report back once I shoot some rounds downrange. Until then, keep reloading my friends.


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