Question 1

Will a 9mm round penetrate a brick wall?

Accepted Answer

A standard 9mm round generally does not fully penetrate a solid brick wall. Brick is a brittle material with high compressive strength; the Poncelet cavity-expansion model predicts the round embeds within the brick or stops at shallow depth, losing most of its energy to fracture and spallation. Exact penetration depends on velocity, bullet construction, and brick density. BallisticEngine computes this per-input.

Question 2

Why does a hollow-point bullet fail to expand after passing through drywall?

Accepted Answer

A jacketed hollow-point (JHP) can clog with gypsum dust when passing through drywall. The hollow cavity fills with material, preventing the bullet from expanding (mushrooming) in the next layer, so it behaves like a full metal jacket (FMJ) round and over-penetrates. This is the scenario tested in FBI Protocol #5 and is a key consideration for home-defense ammunition selection.

Question 3

Why does this model use 60 MPa for brick when brick's compressive strength is only about 20 MPa?

Accepted Answer

Because those are two different measurements. A handbook compressive-strength test squeezes a free-standing cube in a press: the cube is free to bulge sideways as it fails, and red clay brick cracks at roughly 10-30 MPa. A bullet does something else entirely. It punches a cavity in the middle of a wall, where the surrounding brick confines the impact zone and leaves it nowhere to expand. Confined material resists far more than free material. This is triaxial confinement, described by Forrestal's cavity-expansion model. Forrestal, Altman, Cargile and Hanchak (SAND92-1948C, 1994) fitted a dimensionless constant S to concrete penetration data and reported S = 7 to 21 across targets from 13.5 to 96.7 MPa unconfined strength — the weaker the concrete, the larger the multiplier. Their headline finding is that S depends only on the unconfined compressive strength and is independent of the projectile. BallisticEngine therefore applies an effective resistance, sigma_eff = sigma_c multiplied by a confinement factor, rather than the handbook number. Feeding the unconfined value into a penetration model would predict that ordinary handgun rounds pass straight through brick walls, which they do not.

Question 4

How does ceramic body armor destroy a bullet?

Accepted Answer

Hard ceramic armor (such as alumina) defeats bullets through hydrodynamic erosion, described by the Tate-Alekseevskii model. When the target's hardness exceeds the projectile's yield strength, the bullet erodes and shatters on impact rather than penetrating, much like water hitting rock. A soft lead or FMJ bullet retains only a fraction of its mass, while a hardened tungsten-core armor-piercing round can survive because it is harder than the ceramic.

Question 5

What is the difference between BallisticEngine and other ballistic calculators?

Accepted Answer

Most ballistic calculators model exterior ballistics only (trajectory, drop, and wind drift). BallisticEngine additionally models terminal ballistics, computing how deeply a projectile penetrates into different materials using five physics models (Poncelet, Johnson-Cook, KEVLAR fiber, Mohr-Coulomb, and Tate-Alekseevskii erosion). It also exports parameters for Unreal Engine 5 Chaos Physics.

Question 6

Is BallisticEngine free to use?

Accepted Answer

Yes. The core penetration and trajectory calculator is free, including all 18 materials and Unreal Engine 5 export. An optional Pro tier adds DOPE card PDF export, bulk CSV export, and unlimited multi-layer barrier stacking.

Material	ρ kg/m³	σ_c MPa	σ_c dyn MPa	K_IC MPa√m	C_L m/s	Model
Red Brick	1800	15	45–75	0.3–0.5	2700	JH-2
Concrete	2400	30	90–150	0.8–1.5	3800	JH-2
Pine Wood	500	35	40–60	0.4–0.6	3500	Orthotropic
Oak Wood	720	55	70–100	0.6–1.0	4000	Orthotropic
Steel A36	7850	250	350–500	50–80	5940	Johnson-Cook
Steel AR500	7860	1300	1500–1700	80–120	5940	Johnson-Cook
Aluminum 6061	2700	276	350–450	29–37	6320	Johnson-Cook
Tempered Glass	2500	150	300–600	0.7–1.2	5600	JH-2
Kevlar NIJ III	1440	2800	3000–3500	2.5–4.0	7000	Custom
Packed Sand	1600	1–3	5–15	0.05–0.1	500	Mohr-Coulomb
Compacted Earth	1900	0.5–2	3–10	0.03–0.08	400	Mohr-Coulomb

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