The concept of a metal gear is for a tank to fire nuclear warheads from any given terrain without the need of a silo. Rex in particular accomplished this with a rail gun (for stealth purposes), hence me using it for reference.
Also, never doubt the logistics of Metal Gear. They actually do go into VERY explicit detail of all the physics, science, mechanics and logistics of this kind of thing.
http://metalgear.wik.../Metal_Gear_REX
My point was that firing a nuke through a Mass Effect field, it seems to me at least, would be largely redundant. What I meant was that the cannons from a ME gun largely outclass a nuke's yield, so at best you could hope for the damage to be equivalent, in which case...again no difference. Unless you somehow made the nuke's blast delayed to go through an opening in the shields that the initial cannon blast created. But a nuke by itself would likely do next to nothing to a Reaper.
What I know about the Metal Gear Solid frenchise is that they tend to insert obviously fantastic things like certain "super powers" into their lore, and get out of actually having to call it magic by simply saying: "nano machines", as if this could explain everything.
So first you claimed that the explosions "cancel each other", and now you claim that the damage is merely unnoticable, or that it won't be enough to harm a Reaper.
Speculations about the potential damage to a Reaper aside, that's just... not how things work.
First, Like SuperJogi pointed out, explosions can cancel each other out only in very specific circumstances, which shouldn't be relevant here assuming that the munitions are designed by people who know what they are doing.
Second, no addition of a nuke-level amount of energy to any kind of discharge (aside from massive cosmic events like a supernova or a gamma ray burst) can be called insignificant. Even if the kinetic strike itself is measured by megatons of TNT, saying that a few more megatons are insignificant, is the same as saying that there is no difference between "Little Boy" and the "Tsar Bomba".
Third, I specifically mentioned an antimatter warhead. Antimatter is much more efficient than a nuke when it comes to causing a massive explosion.
When a nuke explodes, only a small part of the radioactive material is actually used, the rest is blown away by the explosion. An antimatter warhead on the other hand, merely needs to ensure that the antimatter come into contact with regular matter, and if I remember correctly, you only need a few grams of the stuff to cause a nuke level discharge of energy.
What will happen is this:
A. A Dreadnaught-sized rail-gun round containing a device to hold the Antimatter suspended is fired towards a Reaper.
B. The round impacts a kinetic barrier, discharging most of its energy in various ways - light, heat, kinetic energy, etc.
C. The device holding the Antimatter is destroyed, freeing the Antimatter to come in contact with matter.
D. A secondary massive discharge of energy occurs, possibly disrupting part the initial release of energy from the kinetic-kill-vehicle.
E. Depends on the amount of Antimatter used, the discharge of energy could be massive enough to take down a Reaper's barriers, or possibly even destroy it - remember, according to the lore, it takes around four Dreadnaught-sized kinetic strikes to destroy a Reaper's barriers, I'll leave the actual science to others (SuperJogi?
), but if a few grams of antimatter are enough to cause a small nuke-level explosion, I suspect that you won't need a large quantity - relative to the amount of radioactive material needed in a nuke - to reach the energy-discharge level of four Dreadnaught-sized kinetic strikes.
So, that thing about not being able to defeat the Reapers *conventionally*? It's actually correct, you simply need bigger, meaner, unconventional gunz. Or bombz.
You may still lose because of the Reaper numbers, but you will disrupt their economy and the ratio of Reapers lost / made per cycle enough, that maybe a few cycles down the line they will be destroyed.