Actually from what I'm reading, no a AP 4 Pistol would not be able to damage the wielder of a heavy tactical shield with it's BAR of 6 and integrity of 12 in a single shot. Even if you load it with AP. You'd have to completely deplete the shield's integrity before damage could be done to the wielder.
Barriers as long as they have integrity left and the AP is not greater than the BAR the shot will be stopped.
Page 186-188 for reference.
There are slightly different rules in place for Personal Armor, Tactical Armor, Battle Armor, and Barrier Armor. Having 4 similar systems with subtle differences is a gnarly way to do things, but it's what we have.
As mentioned on page 187 in the Armor Degradation section, Barrier Armor Degradation: "When attempting to determine the effects of an attack against (or through) a barrier, the rules for tactical armor
degradation apply." Emphasis mine.
To my reading, that means that Barrier armor is like tactical armor ONLY in that it takes damage like tactical armor rather than like personal armor. It's been letting damage through that wasn't reduced to 0 by the BAR the whole time, because of:
Per page 185, AP vs BAR, Personal Armor and Barriers: "Any damage that passes through personal armor or barriers (other than tactical armor) is applied as damage to the targeted character."
So in the case of an AP 4 pistol shooting through someone's tactical shield with a BAR of 6, it'd be hitting at -2 to its original AP and BD to whatever personal armor the target might be wearing, or applied directly to the target if there is none. The only reason the shield has an integrity value is to allow it to keep its BAR 6 up until it's so riddled with holes it's no longer any practical use as a barrier and becomes useless.
Paul
verified this is the way it works, as well.So, without a GM applying Rule #1, a shot can shoot through entire buildings, city blocks even. Any barrier without a BAR greater than the AP is treated as not being there at all. I could shoot a sniper rifle at a target 1000 meters away, with a solid block of layers of 'bulletproof glass' barriers 1000m thick extending from the target's skin clear to the barrel of my rifle.. and the shot would still hit the target at full AP/BD if none of the barriers had a BAR greater than the AP.
EDIT:
I'm kicking around the idea of a house rule that applies a reduction in max range of a shot based on what % the BAR was of the AP. For example, a AP 5 rifle will punch right through a BAR 4 barrier, but it should at least be slowed down. So after defeating the BAR 4, the shot's max range is now only 80% of what it would have been without barriers in the way. In the case of AP < BAR, it still punches through to damage something immediately on the far side, but that's it. No shooting an AP4 pistol through a BAR 5 or 6 to hit somone 50 meters beyond the wall... they're only hit IF they're right up with the barrier.