Tech Note

December 27, 1998

TECHNICAL NOTE 20: AMMUNITION, BARRELS, AND ACCURACY OF AR-10B RIFLES

PURPOSE: This technical note provides information concerning the accuracy guaranteed of ArmaLite .308 caliber AR-10(T) rifles

GENERAL: ArmaLite occasionally receives AR-10(T) rifles which are returned for accuracy problems. In virtually all cases, the problem is due to poor ammunition, poor break in procedures, or poor firing procedures.

ACCURACY GUARANTEE: ArmaLite AR-10(T) rifles are guaranteed to meet the same targeting requirements (the center of impact of the rifle) as the M16A2 rifle as spelled out in milspec MIL-R-63997. In addition, they produce 5 shot groups of less than two inches extreme spread at 200 yards, measured between the centers of the extreme shots, when using Federal Gold Medal (GM308M) ammunition or better.

AMMUNITION: Even a fine rifle cannot make good ammunition from poor ammunition. It's amazing how frequently ArmaLite is asked why surplus or imported ammunition shoots poorly. A key fact of ammunition is that a target rifle exhibits its best accuracy with ammunition tuned to THAT PARTICULAR RIFLE. Even high quality ammunition varies between lots, and even the highest quality ammunition may not be quite optimal for a given target rifle.

The AR-IO(T) has a special match grade barrel featuring 1 turn in 11.25 inch rifling. It is superbly accurate when used with proven lots of Black Hills moly coated .308 Win Match, Federal .308M, M852, or other match quality ammunition. Accuracy naturally is less impressive if lower quality ammunition is used, or if less capable lots are used.

BARRELS: The barrel of the AR-10(T) is produced from a custom, target grade blank. For optimum accuracy and improved life expectancy, it absolutely MUST be properly broken in. This timeconsuming process will allow the barrel to smooth out without an accumulation of copper fouling in the pores of the steel. VIRTUALLY EVERY ACCURACY PROBLEM WITH THE AR-10(T) IS CAUSED BY FAILURE TO CAREFULLY BREAK THE RIFLE IN, AND FAILURE TO USE HIGH GRADE MATCH AMMUNITION.

BREAK IN PROCEDURE: To properly break in the barrel, first fire 11 single shots, each shot followed by about 20 strokes of a tight fitting patch bearing J-B bore cleaner (available from Brownells, telephone 515-623-5401) or another high quality paste type cleaner. Failure to use J-B or another paste type cleaner can triple the break in period. Use a Parker Hale or other wrap-around style jag rather than a slotted jag. It is convenient to perform this step from the muzzle, but a brass or plastic rod guide must be used to assure that the rod never touches the rifling at the muzzle.

From shots 12 to 30, clean after each 3 shots. From shots 31 to 50, clean after each 5 shots. From shots 51 to 100 clean thoroughly with a high quality bore cleaner every 10 shots. The barrel should thereafter be cleaned every 20 rounds to assure best match accuracy.

It is best to use solid based, hollow point match bullets for break in: full metal jacket ammunition normally contains a lead slug which is exposed at the base of the bullet. A small amount of lead ablates as the bullet travels down the bore and is deposited on the bore.

Black Hills Ammunition's moly coated .308 Win Match ammunition can reduce or eliminate the normal break in procedure. Accuracy has proven to be outstanding. To procure this ammunition, con- tact either ArmaLite at 800-336-0184, or Black Hills at 800-568-6625.

FIRING PROCEDURE: ArmaLite tests rifles from a wooden bench using only simple sandbags as rests both fore and aft. A more complex machine rest is not needed to meet the minute of angle accuracy guarantee, but proper break in and consistent, sound firing procedure is.

An ArmaLite ST96-10 telescopic sight is used in factory accuracy tests.

Accuracy varies in different firing positions. Bipods, in particular, tend to allow inconsistent rifle movement and are not as conducive to accuracy as a simple sandbag or rest.

Copyright © 1998 ArmaLite, Inc.