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Cast in an AR?  Really?

© 2014 - Ed Harris


italy 093

Ed shooting a SBR in Italy…

If you currently reload for an AR platform, you know that ordinary 55-grain FMJ bullets cost 10+ cents each when you buy in bulk, 1000-up quantities.  Rifle powder costs upwards of $24 a pound if you even can find something suitable.  A pound loads about 270 5.56 rounds, so you are looking at about 9 cents per round just for powder. Buying 8 pound caddies can save you a little bit.

Primers are about $35+ per thousand, again, if you can find them....  So you are very fast approaching 25 cents per shot just in component costs to reload your "free" range pickup brass. That doesn't consider amortization of dies or equipment or put a value on your time to load the stuff.  But it is lots better than $1+ per pop for factory stuff when you cannot find any......

An option is cast bullets!  In a 5.56mm?  Are you nuts?

Well, my neighbor is an avid reader of the CBA forum.  He has learned “what works” by reading the gleanings from postings of other experienced shooters, which greatly shortened his learning curve (Click this link to go to the Cast Bullet Association thread on this topic).  

He has been shooting cast in his M4 clone for several years now.  His has a 16" barrel with military 5.56 chamber.  The 5.56 chamber is larger in the neck and throat diameters than the .223 Remington.  His M4 gas port is only 8" from the bolt face.  QuickLoad, the interior ballistic computer program estimates his port pressure at ~ 12000 PSI. which is as low as you can go with (about 15 grains) of RL7 and still work the action reliably.  After 1,000+ rounds accuracy equals or is better than cheap Russian FMJ ball ammo, the gas system shows no problems at all and the gun runs as clean with his cast reloads as with imported Tula ammo. He says that the best use of cast loads is to preserve the expensive factory stuff for serious work.... They work best for practice and casual shooting.

He follows the advice of others, casting hard bullets, blending linotype from Roto Metals and wheel weights 50-50, running his mold hot enough so that bullets drop uniformly frosted, quenching in water direct from the mold.  Gas checks are crimped on in a .225” sizing die so that the driving bands of the bullet are not sized. Bullets are seated as far out as they can be and still load into and feed from the magazine. His barrel twist is 1 in 9".  Until recently he hadn’t tried any other powder than RL 7, because he keeps that around to load in the .30-30 and 7.62x39, which he also load casts for.   Velocity is 2120 fps using 15 grs. of RL7 and the RCBS 225-55 gr. bullet. Here is the Bullet Mould he uses (Click here to go to Midway USA) - RCBS 2-Cavity Bullet Mold 22-055-SP 22 Caliber (225 Diameter) 55 Grain Semi-Point Gas Check.


This load performs well considering the generous military chamber dimensions. The major problem with shooting cast lead in AR's is their fast twist barrels in current rifles and their sloppy military chambers. Most folks who give up on cast in their ARs do so because they don't understand that the bullet surface which engraves ~ .002" deep simply does not have adequate shear strength to spin the bullet up in such a short distance without slipping the lands and damaging the bullet's integrity. Slow the load down to the minimum which cycles reliably, about 2100-2200 fps and they shoot even better than steel cased Russian ball! 

Computer modeling of slower powders such as Varget through QuickLoad, bullets lighter than about 70 grains, don't develop adequate port pressure at suitable velocities normally useable with cast bullets. Harder, quenched bullets can be driven 2400 fps without leading, but accuracy is best in older 12-inch twist barrels, which limits you to flat based bullets no heavier than about 65 grains. In 9" and faster twists stay below 2200 fps. 

The computer-generated curves predicting pressure vs. bullet travel show that RL7 has the best characteristics to reliably function and efficiency is almost 100% with the powder being fully burned in a 16 inch barrel. A standard 20" length AR barrel is harder to make "work" as its gas port is further down the barrel than it is on the M4 carbine. 

Before the weather turned cold he did some accuracy testing in his M4 with his “standard load" of 15 grs. of RL 7 and the 55 gr. RCBS bullet, for which the double cavity molds are commonly available, and putting a scope on the rifle. Five-shot groups off sandbags at 100 yards averaged well under two inches in aggregate and were more accurate than the junky Tula FMJs. 

A buddy visiting from VA brought his Colt Military/law enforcement model with 7-inch twist barrel. We were pleasantly surprised to see it shoot a one hole 10-shot group of 3/4 inch at 25 yards. The load of 15 grains RL7 would occasionally would short recoil, ejecting the spent casing but without feeding another round.  Additional experiments a 60-grain Saeco mold and 18 grains of H322 or IMR 3031 clocked 2100+ fps and cycled with no signs of leading. Bullets were lubricated with Lee 50/50 Alox-beeswax. Adequate bullet diameter, not less than .225" is critical to accuracy. Load the largest bullet diameter that will chamber/function. Bullets must be of adequate hardness, not less than commercial 92-6-2 “hardball” alloy or 50-50 linotype and wheel weights, especially above 2200 fps. Heavier loads of slower powders such as Varget or 4895 may be needed to boost port pressure in full-length 20-inch ARs. 

To load cast bullets without damage you must inside chamfer case mouths with a shallow-angle Lyman "VLD" deburring tool, and slightly bell the case mouths with a Lyman "M" die   - so that the bullet can be hand started into the case mouth up to the top of its gas check and seated smoothly into the neck without risk of shaving lead. Then, during the seating operation apply a light taper crimp to remove all mouth flare, but not a heavy crimp which could deform the bullet. Also drop-check all rounds 100% in a maximum length cartridge gage to ensure that they will chamber and extract freely. The same as required for any cast bullet load to be used in any semi-auto, AK, Garand, M1 carbine, M1911A1, etc.

There are heavier custom molds available up to 75 grains, optimized for the 5.56mm military chamber, but I have no personal experience with them. Users on other forums report reliable functioning with 18 grains of IMR4895 or Varget for about 2000 fps with the MiHec 75-grain NATO bullet.



Target using MiHEC bullet mould for 22’s in the AR Platform…

The HM2 225-62-1 design is a good choice for either the .223 Remington with 12" twist, or in the faster twists, with appropriate loads. Their six-cavity gang mold is great for quantity production and is VERY affordable at $125, fitting RCBS handles.


Heavy Metals HM2 225-62-1 Bullet Mould…


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