Making 300 Blackout Cases From .223 Brass
The Range Squirrel
My wife’s son is building a 300 Blackout AR pistol, the trouble is factory ammo is made of that precious commodity known as unobtanium. I looked at my stash of prepped .223 brass and decided to do something about it.
Converting .223 to 300Blk is not difficult, however the forums are full of new reloaders, and helping new reloaders is what we are about here, so maybe this will be timely for someone.
The “World’s Cheapest Trimmer” referenced in this post was previously reviewed here. The much more precise “World’s Finest Trimmer” was reviewed in this post.

I owned a Marlin 60 since 1987, but never really got ‘into’ guns until 2011 when I bought my first 9mm pistol. That was soon followed by a .380 and a 12 guage pump, and I was all in. I had done some 20 guage reloading growing up, and threw myself into 9mm and .223 reloading in 2017,ย .380 in 2019 and 7.62×39 in 2020. It is so satisfying to go to the range and string together ever improving groups with ammo I loaded myself; it doesn’t hurt that I’m a little OCD about technical things, the tangible/visible rewards are really gratifying.
I have a nagging but as yet unattained ‘want’ for a .358 Yeti unloader, it just looks like a really cool caliber. My next learning curve, space permitting, is casting and coating.