Tech Tip: Wildcatting for the AR-15 - Part 1 

Brownells Gun Techs™ Caleb and Steve are about to go wild! They are kicking off a new multi-episode series on wildcatting for the AR-15. A wildcat cartridge is any cartridge that's not mass produced by a commercial ammunition manufacturer. Handloaders develop wildcats to fill a need not covered by an existing factory round. A lot of popular cartridges started out as wildcats. Check out our Quick Tip episode, "Caleb's Wild About Wildcat Cartridges" (link below) for more on the wonders of wildcatting.
Nowadays, you do have more factory options for the AR-15 than just 5.56 / .223. There's .300 Blackout, 6.5mm Grendel, 6.8mm SPC, .224 Valkyrie, and even AK rounds. But what if you want something different? Early non-standard AR-15 cartridges that started as wildcats like .450 Bushmaster and .50 Beowulf were cool but used expensive proprietary cases. If you plan carefully, you can use the case for an existing cartridge that fits the AR-15's magazine well. Let's say you want to wildcat something with a .257 caliber bullet.....
Caleb has converted an AR-15 upper receiver to the .25 GPC wildcat round (GPC = General Purpose Cartridge). The .25 GPC uses a 6.8mm Remington SPC case necked down to take a .257" bullet. With its narrower diameter, the projectile will have a higher ballistic coefficient and achieve higher velocities than the 6.8mm bullet - both good things. The higher capacity of the 6.8 SPC case means there's room for a little more "fuel" to motivate that bullet, too. That roomy 6.8 SPC case is actually very adaptable for developing wildcat cartridges for the AR.
Caleb will be loading Starline 6.8 SPC brass with precision CNC-machined solid copper match / competition bullets from Cutting Edge Bullets. What about the dies? Hornady will still make custom dies for you, and Caleb has a set from them for .25 GPC.
And the rifle? Caleb's new .25 GPC wildcat AR has a barrel from Mad Dog Weapon Systems (MDWS), a company that specializes in AR wildcatting. If you have a lathe, a mill, the right reamer, and machining skills, you can make your own barrel from a blank. If you're not so equipped, the folks at MDWS will make a custom AR-15 barrel for you and even configure its gas system.
• Quick Tip: Caleb's Wil...