MCRP 12-10B.1, page 236

A cinder block filled with sand (block will probably shatter) A plate-glass windowpane at a 45-degree angle (glass fragments will be thrown behind the glass) A brick veneer A car body (5.56-mm round will penetrate but normally not exit). d. Wall Penetration. Although most structural materials repel single 5.56-mm rounds, continued and concentrated firing can breach some typical urban structures (See Table B-2). Type Penetration Rounds Required 8-inch reinforced concrete Initial Loophole 35 250 14-inch triple brick Initial Loophole 90 160 12-inch cinder block with single-brick veneer Loophole Breach hole 60 250 9-inch double brick Initial Loophole 70 120 16-inch tree trunk or log wall Initial1 1 to 3 12-inch cinder block (filled w/sand) Loophole 35 24-inch double sandbag wall Initial1 220 3/8-inch mild steel door Initial1 1 1Penetration only, no loophole Table B-2. Structure Penetration Capabilities of the 5.56-mm Round Against Typical Urban Targets (Range 25 to 100 Meters) (1) The best method for breaching a masonry wall is by firing short bursts (3 - 5 rounds) in a U-shaped pattern. The distance from the gunner to the wall should be minimized for best results—ranges as close as 25 meters are relatively safe from ricochet. Ballistic eye protection, a protective vest, and a helmet should be worn. (2) Ball ammunition and armor-piercing rounds produce almost the same results, but armor-piercing rounds are more likely to fly back at the firer. The 5.56-mm round can be used to create either a loophole (about 7 inches in diameter) or a breach hole (large B - 4 MCWP 3-35 .3