I think before readers spend their hard earned cash on a brick or cinder block structure (thinking it is much safer then stick framed construction) then watching all three parts of this [“Concealment Doesn’t Equal Cover”] video  is essential. All [high power] rifles (.223, 7.62×39, .308) and 12 gauge slugs went through normal brick and [hollow] cinder block construction. Just food for thought. – Ryan
JWR Replies: I first posted a link to that Dahlgren/Marine Corps training video in SurvivalBlog in December of 2006 . There was also a discussion of this topic in July of 2007 ., following my initial reply , in which I recommended supplementary sandbagging.
I do not recommend standard hollow cinder-block construction to my consulting clients. Instead, I recommend super-insulated masonry, preferably with an air gap. (Although a rock facade directly over poured masonry or brick works fairly well.) The first wall typically breaks up .30 caliber or smaller projectiles, and the second wall then nearly always stops them. This design will also stop individual 12 gauge slugs, but not .50 BMG  hits.
The bottom line is that typical stucco-covered wood frame construction is pitiful, but two-course brick (two thicknesses of bricks) or concrete-filled cinder block walls offer some protection. They are certainly not absolute protection, but they are much better than wood frame houses, which offer hardly any protection at all from high power .30 caliber bullets. Even super-insulated masonry construction will not stand up to repeated, well-aimed high power .30 caliber rifle fire. Tests at the Box-o-Truth  web site show that short of pouring 20 inch thick reinforced concrete, sandbags are just about the only truly reliable protection from well-aimed repetitious rifle fire. If I were expecting incoming rifle fire, even if I lived in a poured, reinforced concrete house or a Monolithic dome house, I would still construct interior supplementary fighting positions. These would have room for a cot, and be set back a few feet from windows, per current MOUT  doctrine. These would be built of sand bags, with 2″x10″ or 2″x12″ boards built into boxes (sans ends) to provide firing ports. Sandbags are presently cheap and plentiful. But they someday may be highly sought after, so it is important to lay in a large supply (with extra for barter and charity) before the balloon goes up! (SurvivalBlog reader “MurrDoc” recommended Saddleback Materials in Lake Forest, California  as a good source for sandbags. Phone: (800) 286-7263.)