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July 20th, 2023

.300 Blackout Fired in .223 Rem AR — Recipe for Disaster

.300 AAC Blackout 300 BLK kaboom accident blowup cartridge failure barrel .223 Rem 5.56
Photos and Facebook post by Tactical Rifle Shooters

Yet another .300 Blackout disaster. Unfortunately, that .300 Blackout cartridge can fit in a .223 Rem chamber. Shooting a .308-caliber bullet in .223 bore is a recipe for disaster.

.300 AAC Blackout 300 BLK kaboom accident blowup cartridge failure barrel .223 Rem 5.56

.300 AAC Blackout 300 BLK kaboom accident blowup cartridge failure barrel .223 Rem 5.56 The .300 AAC Blackout aka “300 BLK”, is a compact 30-caliber cartridge designed to work in AR-15 rifles. It has a shorter cartridge case to accommodate the bigger 30-caliber bullet while still fitting in a standard AR-15 magazine. Unfortunately, that’s the danger. A careless shooter can toss a .300 Blackout cartridge in with .223 Rem rounds without noting. And because the case-head size is the same as the .223 Rem (5.56×45) the rifle’s bolt assembly will happily chamber and fire the .300 BLK round. Problem is, that forces a .308 diameter bullet down an undersized .223-caliber bore. Not good!

This images were provided by Tactical Rifle Shooters on Facebook. The message was clear: “Don’t try to run 300 Blackout in your .223/5.56mm. It won’t end well. The problem is identical rifles and identical magazines but different calibers.”

Image from Accurate Shooter Forum. Cutaway shows the jammed .30-Cal bullet:
.300 AAC Blackout 300 BLK kaboom accident blowup cartridge failure barrel .223 Rem 5.56

For those who MUST have a .300 Blackout, here are some things you can do:

1. Use different colored magazines for .300 Blackout vs. .223 Rem.
2. Fit all your uppers with caliber-labeled ejection port covers.
3. Mark .223 Rem upper handguards with the caliber in bright paint.
4. Mark all .300 BLK Rounds with heavy black marker.

.300 AAC Blackout 300 BLK kaboom accident blowup cartridge failure barrel .223 Rem 5.56

Comments by Folks Who Viewed these .300 Blackout Disaster Photos:

“The .300 Blackout is simply a badly-designed round. A properly-designed round would have had a feature in the shape that would have prevented cross loading in the first place.” — D. Santiago

“I almost made that mistake… I had a magazine of 300 BLK inserted in my .223/5.56 all night. Fortunately, I never pulled the trigger. Once I realized the mistake, I almost got ill. [After that incident] I no longer own a 300 BLK.” — B. Welch

“Happened to me hog hunting from a helo. Gun exploded in my face.” — B. Hood

“Fire-forming projectiles [is] so wrong in centerfire!” — M. Stres

“Had some dude come into the store the other day wanting .300 Blackout ammo to shoot in his 5.56 AR. It took 15 minutes of explaining for him to understand you got to have a .300 Blackout Upper!” — R. Williams

Permalink Bullets, Brass, Ammo, Gunsmithing, Tactical, Tech Tip 2 Comments »

July 20th, 2023

6mm Creedmoor — How Velocity Changes with Barrel Length

6mm 6.5 Creedmoor rifleshooter.com Bill Barr barrel length cut-down velocity test chronograph Magnetospeed chrono

A while back, our friend Bill Marr of Rifleshooter.com conducted a fascinating 6mm Creedmoor barrel cut-down test that reveals how velocity changes with barrel length. This time Bill started with a 24″ Proof Research stainless steel barrel on a Howa action. Bill says this was a well-used barrel, with over 1800 rounds through it. So, the velocities might be a bit different than a new barrel of similar length. Bill cut the barrel down in one-inch increments. Here are some results from the test:

24″ Velocity: 2893 FPS | 20″ Velocity: 2755 FPS | 16.1″ Velocity: 2598 FPS

CLICK HERE for FULL TEST REPORT on RifleShooter.com »

6mm 6.5 Creedmoor rifleshooter.com Bill Barr barrel length cut-down velocity test chronograph Magnetospeed chrono

6mm 6.5 Creedmoor rifleshooter.com Bill Barr barrel length cut-down velocity test chronograph Magnetospeed chrono For this latest test, Rifleshooter cut the barrel in one-inch increments from 24″ to 16.1″ (just over legal minimum). Velocities were measured with a MagnetoSpeed V3 chronograph mounted on arm attached to the stock. This allowed the chrono to be adjusted inwards as the barrel was cut shorter, inch by inch.

For the 6mm Creedmoor cartridge, Bill loaded Hornady 108gr ELD Match bullets over 41.5 grains of Hodgdon H4350 with CCI 200 primers in new Starline brass.

The results were interesting to say the least. Bill reports: “Muzzle velocities ranged from 2,893 ft/sec at 24″ to 2,598 ft/sec at 16″ for a decrease in muzzle velocity of 295 ft/sec. Muzzle velocity changes per inch of barrel length ranged from 6 ft/sec per inch between 20 and 19 inches to 63 ft/sec per inch between 19 and 18 inches. Average velocity change per inch of barrel length was 37.9 ft/sec.”

Bill concludes: “An average drop of 37.9 ft/sec/inch of barrel is fairly significant and is what would be expected with a fast moving 6mm cartridge like the 6mm Creedmoor. While I’m used to seeing 6mm Creedmoors with slightly longer barrel lengths than 24″, when coupled with a sound suppressor the additional length can make moving the rifle quickly more difficult.

I’d suggest staying with longer barrel lengths wherever possible with this cartridge. At shorter lengths, it does give up more performance than its big brother the 6.5 Creedmoor.”

More 6mm Creedmoor Velocity Data from 2017 Cut-Down Test

If you’re curious about 6mm Creedmoor velocities at longer barrel lengths, back in 2017 Rifleshooter completed a 6mm Creedmoor barrel cut-down test from 31 inches all the way down to 17 inches. The test included four bullet types from 95 grains to 110 grains. With the 110gr Sierra MK, velocity at 31″ was an impressive 3110 fps. Surprisingly the velocity didn’t decrease that much for the first few inches. Even at 26″ (a five-inch reduction), measured velocity with the 110s was 3073 fps, a loss of 7.4 fps per inch on average. With a barrel shortened all the way to 20″ however, velocity had dropped down to 2949 fps, a significant (161 fps) loss. CLICK HERE for complete results from that 31″-17″ Barrel Cut-Down Test.