April 21st, 2021

Beyond .223 Rem — The Many Alternative AR Chamberings

AR15 AR AR-15 cartridge alternative
AR-15 Cartridge line-up image from 80% Arms, used with permission. This selection omits our favorite alternative — the 20 Practical (.223 Rem necked down to .204 Caliber).

Instead of using the standard .223 Remington or 5.56x45mm NATO round, you have many options for an AR-15, as shown above. This photo is from Complete Guide to Alternative AR-15 Rounds in the 80% Arms Blog. Some of the most notable alternative chamberings for AR-15s are:

20 Practical — Simply the .223 Rem necked down to .204 caliber. Requires new barrel. Same bolt, same magazines. Best Bang for the Buck.
6.5 Grendel — Moderately expensive, 6.5 Grendel requires a new barrel, bolt, and magazines. Most use the 6.5 Grendel for competitive shooting and/or hunting.
.300 Blackout — Moderately expensive, the .300 Blackout requires a barrel change. This is used for home defense, and hunting. WARNING — with some bullets this round can be chambered in a .223 Rem barrel, with disastrous consequences.
.458 SOCOM — Pretty expensive, requires new barrel and bolt. The .458 SOCOM round is typically used for hunting though it was originally designed for Close Quarters Battle (CQB).
.50 Beowulf — The most expensive alternative AR-15 cartridge, this requires new barrel and bolt. The .50 Beowulf was created for game hunting, but most hunters use something more practical.

Of these five options, our top choice is the 20 Practical, followed by the 6.5 Grendel. Check out our featured 20 Practical AR Rifle Report. This 20 Practical cartridge is highly effective on small varmints, and has shown outstanding accuracy in AR-platform rifles crafted by Robert Whitley.

20 Practical — High-Velocity, Affordable Alternative

The 20 Practical is simply a .223 Remington necked down to .204 caliber. This efficient little cartridge can launch 32-grainers at over 4200 fps, with impressive results on P-Dogs. This makes the 20 Practical a great choice for an AR-based varmint rifle.

20 Practical20 Practical Ultimate Varminter
A decade ago, as a “proof-of-concept”, AccurateShooter.com created a 20 Practical AR15 Ultimate Varminter with a custom 20-caliber upper from Robert Whitley of AR-X Enterprises, LLC. That project rifle was ultra-accurate — every 5-shot group out of the gun was less than the size of a dime. That gun was auctioned off, but Robert Whitley continues to produce custom 20 Practical AR15 uppers. (The 20 Practical cartridge is simply the .223 Rem necked down to 20 caliber — you can use standard .223 brass and load with standard .223 Rem dies. Just swap in a smaller expander and use smaller neck bushings.)

The 6.5 Grendel — Accurate, Plus Good for Hunters

The 6.5 Grendel round is one of the most accurate cartridges for the AR-15 platform. The 6.5 Grendel round offers a larger-diameter, .264-caliber (6.5mm) bullet running at good velocities. This provides ample energy for smaller game and deer. The 6.5 Grendel is often used for hunting deer up to 300 yards.

6.5 Grendel

History of the 6.5 Grendel Cartridge
The 6.5 Grendel originated as a 6mm PPC necked up to 6.5 mm. After Alexander Arms relinquished the “6.5 Grendel” Trademark, the 6.5 Grendel was standardized as an official SAAMI cartridge. It has become popular with target shooters and hunters alike because it is accurate, efficient, and offers modest recoil. Good for small to medium game, the 6.5 Grendel is becoming a popular chambering in lightweight hunting rifles, such as the Howa 1500 Youth Model.

6.5 Grendel Saami Hornady Brass

The .300 Blackout — Risky Business

The .300 Blackout appeals to folks who want a .30-caliber defense round. This can be loaded at various velocities. Loaded at subsonic speeds and shot with a suppressor, the .300 BLK offers very low sound levels. 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 5.56The .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 Remington.
2. Mark .223 Rem upper handguards with the caliber in bright paint.
2. Fit all your uppers with caliber-labeled ejection port covers.
4. Mark all .300 BLK Rounds with heavy black marker.

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April 21st, 2021

CMP Warns Against High-Pressure Loads in Garands and 1903s

CMP .30-06 ammo ammunition safety warning M1 Garand m1903 1903a3 50000 CUP high pressure

The Civilian Marksmanship Program (CMP) has issued an ammunition safety advisory to all users of M1 Garands, M1903s, and M1903A3 rifles. Ammunition that is loaded beyond 50,000 Copper Units of Pressure (CUP) and using bullets weighing more than 172 grains should be limited to modern rifles, and NOT USED in old military rifles aged 70+ years.

CMP .30-06 ammo ammunition safety warning M1 Garand m1903 1903a3 50000 CUP high pressure

After this warning was issued by the CMP, the California Rifle and Pistol Association (CRPA) provided further safety recommendations for owners or older firearms:

CRPA Ammunition and Older Firearms Guidelines
Many of us have either purchased or inherited firearms in excess of 25 years of age. The issue … noted as an example by the Civilian Marksmanship Program in regards to certain ammunition leads as they apply to the M1 Garand is not isolated to that particular firearm. The CRPA… has seen similar issues exposed with other [older] firearms when using modern loads. We strongly advise you to check with the manufacturer for recommended load limitations before purchasing modern ammunition for an older firearm.

CRPA also recommends these safety procedures:

Have a gunsmith check your older firearm for safety prior to using it.

Take a reloading class to help develop a safe load for your older firearm.

Inspect older ammunition for defects such as a green patina or rust build up on the cases or crystallization on the projectiles. If defects are observed, the CRPA suggests disassembling the ammo into components for proper recycling and disposal.

Storage of Ammo for Older Rifles
The CRPA also cautioned that you should be cautious about older ammo that may be decades old, including old milsurp ammunition. The CRPA advises:

1. Store ammunition in a cool, dry, location where little temperature fluctuation occurs.
2. If storing ammunition in an air/watertight ammo can, utilize water absorbent silica packs and place packs in the can with the ammunition.
3. Conduct periodic checks every 12-24 months and replace the silica packs as needed.

CRPA Notification provided by EdLongrange


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April 21st, 2021

How to Verify Your Scope’s True Click Values — Box Test

Click Optics MOA turrent verification test

Let’s say you’ve purchased a new scope, and the spec-sheet indicates it is calibrated for quarter-MOA clicks. One MOA is 1.047″ inches at 100 yards, so you figure that’s how far your point of impact (POI) will move with four clicks. Well, unfortunately, you may be wrong. You can’t necessarily rely on what the manufacturer says. Production tolerances being what they are, you should test your scope to determine how much movement it actually delivers with each click of the turret. It may move a quarter-MOA, or maybe a quarter-inch, or maybe something else entirely. (Likewise scopes advertised as having 1/8-MOA clicks may deliver more or less than 1 actual MOA for 8 clicks.)

Nightforce scope turretReader Lindy explains how to check your clicks: “First, make sure the rifle is not loaded. Take a 40″ or longer carpenter’s ruler, and put a very visible mark (such as the center of an orange Shoot’N’C dot), at 37.7 inches. (On mine, I placed two dots side by side every 5 inches, so I could quickly count the dots.) Mount the ruler vertically (zero at top) exactly 100 yards away, carefully measured.

Place the rifle in a good hold on sandbags or other rest. With your hundred-yard zero on the rifle, using max magnification, carefully aim your center crosshairs at the top of the ruler (zero end-point). Have an assistant crank on 36 (indicated) MOA (i.e. 144 clicks), being careful not to move the rifle. (You really do need a helper, it’s very difficult to keep the rifle motionless if you crank the knobs yourself.) With each click, the reticle will move a bit down toward the bottom of the ruler. Note where the center crosshairs rest when your helper is done clicking. If the scope is accurately calibrated, it should be right at that 37.7 inch mark. If not, record where 144 clicks puts you on the ruler, to figure out what your actual click value is. (Repeat this several times as necessary, to get a “rock-solid”, repeatable value.) You now know, for that scope, how much each click actually moves the reticle at 100 yards–and, of course, that will scale proportionally at longer distances. This optical method is better than shooting, because you don’t have the uncertainly associated with determining a group center.

Using this method, I discovered that my Leupold 6.5-20X50 M1 has click values that are calibrated in what I called ‘Shooter’s MOA’, rather than true MOA. That is to say, 4 clicks moved POI 1.000″, rather than 1.047″ (true MOA). That’s about a 5% error.

I’ve tested bunches of scopes, and lots have click values which are significantly off what the manufacturer has advertised. You can’t rely on printed specifications–each scope is different. Until you check your particular scope, you can’t be sure how much it really moves with each click.

I’ve found the true click value varies not only by manufacturer, but by model and individual unit. My Leupold 3.5-10 M3LR was dead on. So was my U.S.O. SN-3 with an H25 reticle, but other SN-3s have been off, and so is my Leupold 6.5-20X50M1. So, check ‘em all, is my policy.”

click values scope Mrad moa scope test

From the Expert: “…Very good and important article, especially from a ballistics point of view. If a ballistics program predicts 30 MOA of drop at 1000 yards for example, and you dial 30 MOA on your scope and hit high or low, it’s easy to begin questioning BCs, MVs, and everything else under the sun. In my experience, more than 50% of the time error in trajectory prediction at long range is actually scope adjustment error. For serious long range shooting, the test described in this article is a MUST!” — Bryan Litz, Applied Ballistics LLC.

Bryan also uses a Tall Target Test to determine true click values. CLICK HERE to read a detailed, explanatory article about Litz’s Tall Target Test.

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