Does my homeowner's insurance pay for the damage to their house?
Highly unlikely, you could ask your insurance company, but I would't bet on it
Am I potentially liable for some sort of civil charges because of the damage?
Almost certainly, if you swerve your car to avoid a dog and crash into their home then you can be sued for the damages and any duress caused. i can't imagine that punching their home with holes is any different legally.
Would I get charged with vandalism or something similar?
Depending on the situation you could also be charged with criminal negligence, reckless endangerment or other firearms offenses, it depends on your local ordinances and safety laws you're allowed to defend yourself, but you can't destroy the block or endanger bystanders to do so.
For instance if you're engaging with something that is grossly overpowered, say a 50 BMG I'd expect that you would be charged with something. Likely this would come down to a defense/prosecution of "would a reasonable and prudent man believe" arguments. So based on that you could look at the common applications of a rifle/round combo and make a decision.
Problem is that with FMJ rounds in a military style weapon then the prosecution is going to look at military applications of those rounds. What's below will be used on the prosecution side if they're smart in particular section b subsections 2 and 3 (common house construction materials).
from FM 3-06.11 Combined Arms Operations in Urban Terrain Chapter 7
7-2. RIFLE, CARBINE, AND SQUAD AUTOMATIC WEAPON
<snip>
b. Weapon Penetration. The penetration that can be achieved with a 5.56-mm round depends on the range to the target and the type of material being fired against. The M16A2, M4, and M249 achieve greater penetration than the older M16A1, but only at longer ranges. At close range, the weapons perform the same. Single 5.56-mm rounds are not effective against structural materials (as opposed to partitions) when fired at close range—the closer the range, the less the penetration.
(1) 5.56 mm Maximum Penetration. For the 5.56-mm round, maximum penetration occurs at 200 meters. At ranges less then 25 meters, penetration is greatly reduced. At 10 meters, penetration by the M16 round is poor due to the tremendous stress placed on this high-speed round, which causes it to yaw upon striking a target. Stress causes the projectile to break up, and the resulting fragments are often too small to penetrate.
(2) Reduced Penetration. Even with reduced penetration at short ranges, interior walls made of thin wood paneling, Sheetrock, or plaster are no protection against 5.56-mm ball ammunition rounds. Common office furniture, such as desks and chairs, cannot stop these rounds, but a layer of books 18 to 24 inches thick can.
(3) Wood and Cinder Blocks. Wooden frame buildings and single cinder block walls offer little protection from 5.56-mm rounds. When clearing such structures, soldiers must ensure friendly casualties do not result from rounds passing through walls, floors, or ceilings.
(4) Armor-Piercing Rounds. Armor-piercing rounds are slightly more effective than ball ammunition in penetrating urban targets at all ranges. They are more likely to ricochet than ball ammunition when the target presents a high degree of obliquity.
c. Protection. The following common barriers in urban areas stop a 5.56-mm round fired at less than 50 meters:
- One thickness of well-packed sandbags.
- A 2-inch concrete wall (nonreinforced).
- A 55-gallon drum filled with water or sand.
- A small ammunition can filled with sand.
- A cinder block filled with sand (block will probably shatter).
- A plate glass windowpane at a 45-degree angle (glass fragments may be thrown behind the glass).
- A brick veneer.
- A car body (5.56-mm rounds penetrate but may not always 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 7-2).
(1) Breaching Masonry Walls. The best method for breaching a masonry wall is by firing short bursts (three to five 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, protective vest, and helmet should be worn.
(2) Ball and Armor-Piercing Ammunition. Ball ammunition and armor-piercing rounds produce almost the same results, but armor-piercing rounds are more likely to fly back at the shooter. The 5.56-mm round can be used to create either a loophole (about 7 inches in diameter) or a breach hole (large enough for a man to enter). When used against reinforced concrete, 5.56-mm rounds cannot cut the reinforcing bars.
YMMV IANAL, etc. I personally would not use 55gr or 62gr FMJ 5.56mm for home defense in a home with common construction and at common US ranges.
