Ok, been quite some time since I took electromagnetism, but let's see what I can recall:

If memory serves in principal a Railgun consists of the following:

In principal the Railgun has 4 components:

 1). 2 conductive Rails on either side of the projectile.  The Rails should be fiarly long compared to the gap between them, as longer rails mean more acceleration for the projectile

2). A conductive solid or plasma bridging the Gap between the two Rails- This solid or Plasma is palced behind the projectile and is what is actually accelerated by the Railgun- the Projectile is accelerated by this object pushing it from behind.  Despite completing the circuit between eh Rails, this component like the projectile is not actually attached to the Rails and can slide freely along the rails.   This component also must be affected by magnetism.

3).  The projectile it's self.  Note for a highly conductive projectile this may be the same component as #2

4). A VERY powerful source of electricity.

they Are wired as followings:

Each column of # denotes one of the two Rails from 1)

VVVV denotes the conductive object from 2)

OOO represents the projectile

(+)[powersource](-)

 |                       |

 |                       |

 |                       |

   |                    |

    |                  |

     |                |

      #VVVVVVV#

      # OOOOO #

      #             #

      #             #

      #             #

      #             #

      #             #

      #             #

Electricity flows down the the negative Rail, accross the VVVVVV and back along the positive Rail to the powersource.  WHile I'll spare you the nitty gritty detailed, at the precise point of VVVVV(between the two rails at the point where the circuit is completed), the entire force of the magnetic field created by the flow of electrons happens to point in the direction the railgun is facing  and since VVVVV it's self is move forward by the force of it's circuit's magnetic field.   If memory serves at the position of VVVVV the Magnetic Field of the positive and negative Rail both are exerting force in the same direction- But I could be remembering this last bit wrong.

Ordinarily moving even a  bit forward would move VVVVVV out of the butter spot where all of the magnetic field's profce is projected in a single desired location, but as VVVVV moves, the nature of the circuit changes as VVVVV it's self is part of the circuit.  Said "butter" spot will always be between the rails at the point where the two Rails are connected into a circuit- Which is to say VVVVV will always be at the point where the desired magnetic field force is present.

So long story  There is a large force pushing componenet 2, which in turn exerts an equal force on the projectile along the entire Rails.  Force causes acceleration, which means especially on longer rails this sustained acceleration can generally result in much higher projectile speeds then conventional weapons which only give a single initial burst of force and thus acceleration.

Of course this is also a bit of a simplification of the whole truth, but in principal is really just taking advantage of the nature of a square circuit's magnetic field.

hard to say being that modern science doesn't really have much i nthe way of force shields 

That said I'd say in the sins lore "no".  They would have better penetrating power in the sense that Railsguns tend to be very high damage weapons and as a result may take less shots to drop shields.  But from Sins abilities they have never demonstrated any ability to penetrate shields.

If the Railgun is firing an explosive round, I'd definitely say the answer is no- the round is just as likely to explode on hitting the shield as anything else.

Otherwise I could see an argument beign made- after all, Railguns are very very good at penetrating conventional physical Armor.

That said though, ultimately I think I'd go with "no"- The TEC are supposed to be the least technologically advanced race by a significant margin-  Having them possess a weapon that can easily bypass both armor(Railsguns unquestionably excel at this) and shields of the more technologically advanced races seems a bit off to me.

 True, but at the same time in actual warfare if something is that overpowered before long everyone is using it.  And being that the Advent & Vasari haven't adoptedthe Railgun tech I think it can be assumed that Railguns aren't utterly superior weapons to other common weapon types.

It's certainly not outside the Other race's reach technologically-  Railguns are actually pretty simple in terms of the science involved(especially considering how technologically advanced compared to modern times all three races are).  

Nothing to say on these later points- Well this may be influenced by me having a detist appointment in 15 minutes and needing to book it now 

From the Sins universe, it does not appear that any speed will allow it to bypass shields. Phase missiles work by traveling between dimensions then rematerializing inside the target's hull. That's the only way to bypass shields.

Original: Pretty standard military warfare, TEC gets invaded by Vasari, loses a lot of ground, eventually mounts a counter attack and stars winning. Then Advent invade, forcing them to split forces.

Entrenchment & Diplomacy: Stalemate between empires as Starbases makes campaigns take far longer, less likely to succeed. No one appears to have the edge.

Rebellion: All hell breaks lose as the factions split apart. The Vasari are certainly moving a lot, with the Loyalists raiding as many planets as possible for resources, while the Rebels are probably moving to the edge of the galaxy while they negotiate with the other factions. The TEC Rebels are going to be attacking any Advent or Vasari group that looks vulnerable, while the Loyalists are staying put and building more starbases. Hard to tell what the Advent would be doing strategically, the Loyalists are probably mostly static, spreading culture with the occasional military campaign. No idea about the Advent Rebels.

Some of this information was found by looking closely at the intro cinematics, including the TEC capital. Someone put it in a thread but I can't find where it went.

https://en.wikipedia.org/wiki/Railgun

https://en.wikipedia.org/wiki/Coilgun

The TEC Rebels Ragnarov Titan uses a Rail gun as primary weapon.... and Gauss Guns as secondary weapons.

Railgun = Railgun

Gaus Guns = Coilgun