AR-Alternate Calibers

Dealer’s choice: Bigger, faster, slower or quieter?

A “new” AR may only mean a new upper assembly. Here’s Glen’s with a choice of .223 or .300 Blackout.

Sometimes it seems nobody really likes the .223 Remington. Ever since the inception of the AR15 60 years ago, this little round has been under a magnifying glass. It honestly isn’t so bad, especially not for the uses most of us request from our AR-platform firearms.

However, your AR15 doesn’t have to be .223! There are so many choices now. I’ll confine this bit here to a scant few of the most popular and, I think, also those having the greatest capacity to redefine — or at least re-purpose — an AR15.

Notice I didn’t just say, “make it better.” Define better! The question is “Better for what?” Also, for this first look into alternate cartridges, I’m going to focus on those with the most straightforward of conversions.

Many cartridge changes require parts swappage — different bolts, different magazines, upper receiver modifications and more. The original .223-class of cartridge options use a 0.378" bolt face but others need larger diameters. Along with a larger-diameter bolt face, there can also be small differences in extractor geometry, bolt lug dimensions and bolt face recess depths. Here’s some advice: The best results come from using a proprietary bolt engineered for the specific cartridge you’ve chosen.

The hotrod Nosler and Valkyrie produce gas aplenty. Easiest way to counter that ill
effect is with a valved gas block, like this Odin Works Tuneable.

The .300 HAM’R comes close to matching .30-30 ballistics.

.300 Blackout

This ominous sounding round came from longtime wildcatter JD Jones and is, pretty much, a .221 Remington Fireball with a .308 neck. The Fireball was based on a shortened .222 Remington (some say .223) and developed for the old Remington XP100 bolt-action pistol.

Originally called the .300 Whisper, Advanced Armament Corporation secured production-cartridge status (which means it got SAAMI-certified) and called it the .300 AAC Blackout.

It was originally developed as a subsonic round, which is the reason for the bigger bullet (to retain more impact effect at slower speed). Nowadays, though, supersonic loadings with bullets up to 135 grains are its common application. Short course: the idea is to provide 7.62x39-level power in a round fitting into original AR15 architecture. It does! Same bolt, same magazine, same magazine capacity.

The short 1.4" case and bigger bullet doesn’t give much room for propellant. Therefore, it’s a faster-burning fuel and produces less gas. Carbine-length gas systems are routine. Because of this (and to offset velocity/energy loss from a short barrel), I think the AAC Blackout is the best choice for anyone wanting a pistol-format AR.

One of Glen’s faves is the 6.5 Grendel (right). It grew from the wildcat
“Tallboy PPC” (center) that grew from a PPC (left).

6.5 Grendel

This is one of my top recommendations for those looking for more energy and tight groups at longer ranges in a ready-to-go package (bolts, magazines, barrels, brass and loaded rounds).

Bill Alexander of Alexander Arms created this round based from experiments NRA High Power Rifle competitors (me included) were running on PPC “tall-boys.” It’s a PPC case with the shoulder elevated, thereby increasing its internal capacity after fire forming.

Bill improved on this wildcat and, as suggested, created a fully SAAMI-certified round. The Grendel has the well-proven PPC silhouette — 30-degree shoulder, “short/fat” overall design — which gave the PPC a reputation as “the world’s most accurate cartridge.”

Here’s a few “factory” rounds now commonly found inside AR15 uppers (from left): .
223 Remington, .224 Valkyrie, .22 Nosler, 6.5 Grendel, 6.8 SPC, .300 Blackout.

.22 Nosler and .224 Valkyrie

I know these are two different rounds, but I group them together because they each set out to do essentially the same thing — maximize velocity in .224-caliber bullets.

The .22 Nosler is a fully proprietary design (no parent case) with a rebated case rim to fit a standard .223 bolt face. Case length is 1.76 (same as a .223) and it has the hot-rod standard 30-degree shoulder.

It has a much bigger body, much more capacity, much higher velocity — about +300 fps with any weight bullet. It’s pretty much a .22-250 ballistically.

The .224 Valkyrie is from Federal and based on the mil-spec 6.8 SPC so it has a 0.422 case head. Compared to the .22 Nosler, it’s shorter but longer-necked. The idea was to maximize the best balance of velocity and accuracy with the biggest of the .224 bullets (75-90 grains). The shorter case length improves loaded round architecture because these long bullets are not seated as deeply into the case. The result is impressive. Velocity and longer-range accuracy are well improved over .223.

Which is better? The Nosler’s faster, the Valkyrie has better paper-punching potential and upward flexibility in bullet weight. In my experience, however, it’s not a simple “speed or accuracy” choice. One important factor is the Valkyrie is more available.

.300 HAM’R

Last, and maybe saved for best, is a brand-new round from Wilson Combat. Short course: In terms of performance, it’s a radically ramped-up .300 Blackout. It also fits a standard .223 bolt — simple swap.

Wilson based the .300 HAM’R on Kurt Buchert’s good-but-obscure 7.62x40WT which has been available from Wilson for years (Wilson offers over 20 alternate chamberings for its AR-platform guns). Much experimentation refined the round into the .300 HAM’R, and it’s now been SAAMI-certified and is a complete package (for buyers or builders). The cases are 0.040" longer than the 7.62x40WT and a whopping 0.260" longer than the .300 Blackout.

The result? An easy +300 fps beyond the Blackout with 110-135-gr. .308 bullets, which means a solid 2,600 fps with a 110 grain. For hunters, this means a +400 ft. lbs. muzzle-energy increase. It closely matches the good old .30-30 Winchester, which was Bill Wilson’s goal.

And the HAM’R hammers! Accuracy is superb.

There are more alternates to the .223 and I hope to get back on this topic shortly.

Read More Up On ARs Articles

Purchase A PDF Download Of The GUNS Magazine September 2019 Issue Now!