How I cut 5.56 to .300 Blackout brass

| January 31, 2014 | 2 Comments

In the quest to build a super-short AR pistol, I turned towards .300 Blackout as my caliber of choice. 5.56×45 (the “usual” AR caliber) is very velocity dependent and does not do well in shorter barrels. I like 7.62×39 for civilian use, but unfortunately there are all sorts of feeding problems with that cartridge and the AR platform.

So, here we are at .300 Blackout.

The problem with .300 Blackout is that commercially loaded ammunition is scarce and expensive. Bottom of the barrel plinking-grade practice ammunition is about $0.40 a round, compared to $0.23 / round I pay for 7.62×39. Worse yet, ammunition we’d use for defense exceeds a dollar per round.

At current market demand, if you want to shoot .300 Blackout you’re going to need to reload it.

Luckily, that’s a pretty easy proposition. You take a 5.56x45mm case and cut it down. Then you reshape the brass in a resizing die on your press, do the usual reloading steps, cram a .308 bullet on top and call it good.

Commercial reloading component companies make pre-made .300 Blackout brass, but it’s expensive. There are¬†several¬†cottage industry-style mini companies making .300 Blackout brass, down to annealing the neck cases.

If you are a do-it-yourself type of person, then making your own .300 Blackout brass out of spent 5.56 casings is pretty easy.

I recommend a 2″ cut off saw and a special jig made by David Semrad.

Here’s a short video I put together:

About the Author:

Short Barrel Shepherd Short Barrel Shepherd is a regular guy and works to make Web sites and mobile apps easier for people to use. He spends his free time attending fight-focused firearm, knife, and combatives training, motorcycling, writing, and playing games. His daily carry is a Glock 19 pistol and an AR15 .300 Blackout pistol in a backpack.
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2 Comments on "How I cut 5.56 to .300 Blackout brass"

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  1. Marc says:

    Hey man so you have picked up a 300 BLK upper?

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