i think using an ammo to block is useless.. yes it can take an extra impact from a rant or sniping goon
but .. why not use a turret that also does a bit of damage
they cant get passed it untill it blows up anyways.. plus blowing up deals bonus damage 
Point is, turret will blow even if someone repairs it while goon is sniping it. Turret has 190 hp, goon snipes 110 damage per sec. And tyr destroys it, while having about 50 damage from turret. So one way or another, turret is bad blocking device. Armory has 280 hp. If goons throws all barbs on it, total damage is 330 on 2 secs. You must heal atleast 50 damage to survive third blow. Its like 50:50 chance, sometimes you success, sometimes you not. Big disadvatage on arms is, they are to big, humans shoot at him,its hard to go over it and its big target to snipe. So, in some situatsions, its better to use telenode. Advantages are, 310 hp(if you repair, goon cant destroy it with 3 barbs), its harder to snipe, you have faster respawns -> more defending humans. Disadvantages, destroyer gets 1 evo, There are not many places where you can put it as a blocker.
Mostly, it there are alot players, arm or tele as blocker works. If less, then use better turrets on great numbers.