Bolter rifle`s armor penentration is nice though... Armored Ortnok bites the dust after three hits, but to hit that ortnok three times you have to be at kissing range which isn`t something you want to do...
Bear in mind that you can *shoot through most walls* with them, at reduced damage. You can't shoot through the exterior side walls of an intact harvester (too thick, AFAICT), but you *can* shoot through, say, from the ground level to the upper deck through the ceiling/floor, or from right outside the back through the thin walls around the doorway. You can shoot through a window, through the roof of an ordinary building, and nail a target to whom you didn't even have line of sight (with that shooter; *somebody* should spot so you know where to shoot)...
A Bolter has a 'throughwall' factor of 2. The first wall the shot goes through, divides damage by sqrt(2) (to 46-65 from the original 65-85); the second wall, by an additional sqrt(3) (to ~26.5-34.7) and /then/ you subtract the armor's value against the shot's damage weight. Medium alien armor subtracts 22 from the relevant damage weight, so
# walls / no armor / light alien armor (12pt) / medium (22)
0 / 65-85 / 53-73 / 43-63
1 / 46-60 / 34-48 / 24-38
2 / 26.5-34.7 / 14.5-22.7 / 4.5-12.7
So vs. medium armor, a burst through one wall can still hurt nastily (72-114 if you hit 100%), and against an unarmored opponent a three-round burst through two walls is still vicious, but it's not that useful against a medium-armored opponent.
For comparison, a sniper rifle has a throughwall of 1, so it can penetrate one wall, but it has a higher base damage of 105 (always) and the same damage type (normal_heavy), so again 12 or 22 pt reduction.
# walls / no armor / light armor / medium armor
0 / 105 / 93 / 83
1 / 74 / 62 / 52
The coilgun has a throughwall of 3, the same damage type, and a damage of 180+/- 36 (thus 144-216). This results in
# walls / no armor / light armor / medium armor
0 / 144-216 / 132-204 / 122-194
1 / 102-153 / 90-141 / 80-131
2 / 59-88 / 47-76 / 37-66
3 / 29-44 / 17-32 / 7-22
For reference, civvies should have ~5-10 health, Tamans 100-130, Ortnoks 150-190, Shevaars 120-160, Bloodspiders 150. So a three-round Bolter burst through a single wall (100% hit: 138-180, 102-144, 72-114 health for no armor, light alien and medium alien respectively) is pretty significant. Now consider that judging from the 2.3.1 source there seems to be no penalty to precision or accuracy for shooting at a completely obscured target (just significantly reduced damage for when you hit, up to the number of thin walls allowed -- zero for most weapons), and therefore the odds of hitting somebody who's just on the other side of the wall/ceiling are pretty high, and that the aliens have no weapons which can return fire through a solid wall...