FT: ST designing, railgun

I just can't leave it alone.  I tinker and tinker and tinker. I've
modified the ship designs about 3 times already.  But what fun!
I reduced the Fed CA's screen level to 1, removed a class-1,
removed a FC, added hangar bays (2 shuttle craft, 
3 mass total), 2 mass of science labs, 1 mass of cargo space.
And then I made a command cruiser.  I added a 360 degree class-2,
1 armor, and 1 space for a "flag" bridge.  Thus jumped the mass
from 84 to 100.  Then I designed a CL.
Now for the Klingon ships:  I split the D7 into two designs;
a D6 at 54 mass with 2 class-3s as disruptors and 1 class-1 as a 
small phaser (token anti-missile/small craft defense); the D7
got 3 class-3s and 2 class-1s.	No hangar bays or science stuff,
these are purely warships (was a Klingon shuttle ever seen?).

I read the rules on the railgun.  I see several problems.
1) Not in the FB.  Small matter, easily modified.  Acceptance by
others is another matter.  Is this "anti"matter?
2) Screens do not affect it, but in ST the E was taking shield
hits from disruptor fire.  Armor could represent this but I
want screens to have some effect.
3) Limited to 1 arc of fire.  So far most of my K designs fit
this but I did expand the arcs by 1 for two of the disruptors
on my new D7.  I have no problem going back to 1 arc.

Back to 2.  My ideas for modifying railguns to be disruptors
for FB and being affected by screens, since the effect I want 
is from an energy weapon and not a mass driver:
Each level of screen modifies the damage die roll by -1.  A modified
result less than 1 has the disruptor class do 1/2 damage, rounded
down.  So a class-1 disruptor will do no damage, a class-2 and
class-3 will do 1 point of damage.  Reduce the cost to 3 per
mass instead of 4 (gee, in line with beam weapons, the class-3
equals a pulse/photon torpedo launcher).
(uh oh, fuzzy memory; mass were 1, 2, and 4 for each class, right?)

Glen