Bullet Resistant Wall Construction
“Based on these tests, it is my professional recommendation, when practical, that we utilize the combination of Oriented Strand Board (OSB) and concrete. For new construction this combination appears to offer the best results at a cost far less than the commercially available ballistic fiberglass.”
The recommendation was made to the city of Boulder, Colorado following a series of bullet penetration tests by the city facility manager William Boyes, who concluded that the best bullet resistant wall construction (versus cost) is 5/8″ Gypsum on 2″X4″ studs with 1 1/8″ OSB (oriented strand board) both sides and cavity filled with concrete. The OSB is simply used as a material strong enough to hold the poured concrete, and the Gypsum is for the interior wall aesthetic appearance (typical drywall).
The bullet penetration tests were performed to determine the ability to withstand penetrations by a number of commonly used bullets (9mm, .45 auto, .357, .44, 12 ga. Slug, .223, .270 Win). They were selected based on press coverage of incidents around the nation, as weapons/calibers commonly used in attacks on citizens. These range from what are commonly referred to as “plinking” to “big game” calibers. All test shots were from 7 yards downrange.
The materials cost for the recommended solution was determined to be a little more than $3 per square foot (apprx. $100 for a 4×8 section). Of course your price will vary, and does not factor in labor costs (which were estimated at the time to be similar to the materials cost itself). To do it yourself may be relatively straight forward for those of us who can do this sort of thing… but… (disclaimer: your building codes may vary, so do your due diligence).
Typically, concrete has a density of 150 pounds per cubic foot (150lbs/ft), which means that a block of concrete that is one foot wide, one foot long, and one foot high would weigh 150 pounds. The gap in a 2×4 constructed wall (which is actually 1.5 x 3.5) is 9.3 cubic feet within a 4×8 section (typical size of plywood/gypsum/osd, etc.). Therefore, each 4×8 section when filled with concrete will have a downward force weight of 1,400 pounds. Be sure that your floor/foundation can support it, etc.
ballistic test source: http://www.huts.com/Huts%27sBallisticTest.htm