You can do a lot of creative things with breaching rooms that have Combine soldiers in them.
Actually, the trick is not to breach the room. You can use barrels and crates to make yourself cover, and you can set oxygen tanks or gas containers next to the doorway to shoot and cause a soldier or two to burst into flames.
Get close and in cover with the shotgun, throw a grenade through the door, maybe one dies, they all come out, shoot the propane tank to catch one on fire and block up the door, shoot them as they come through.
Aim for the head - but the goofy-ass FIRE BOTH “BARRELS” thing does help, I’ll admit.