A Railgun is a hybrid turret that fires hybrid charges. Railguns are generally accurate at among the longest ranges of any turrets ingame. Caldari and Gallente ships often receive significant bonuses to railgun usage.
From the ingame description:
 "A railgun uses magnetic rails to fire solid chunks of matter at hypersonic speeds. The accurate range of railguns is very good, but due to technical limitations it cannot use onboard guidance. This results in a fairly rapid drop in accuracy at extreme ranges. Requires hybrid ammo types: antimatter, iridium, iron, lead, plutonium, thorium, tungsten, uranium."
Frigatesize railguns. (Click link for a more complete list.)
Civilian
This railgun does not require ammunition.
Name 
Meta 
Optimal Range 
Accuracy Falloff 
Rate of Fire 
Damage Modifier 
CPU Usage 
Powergrid Usage 
Tracking Speed 
Activation Cost

Civilian Gatling Railgun 
0 
875m 
3,500m 
2.0s 
0.5x 
4tf 
6MW 
0.5 rad/s 
1.00 Energy

75mm
Can load up to 160 smallsized hybrid charges.
Name 
Meta 
Optimal Range 
Accuracy Falloff 
Rate of Fire 
Damage Modifier 
CPU Usage 
Powergrid Usage 
Tracking Speed 
Activation Cost

Gatling Rail I 
0 
6,000m 
3,000m 
2.6s 
1.5x 
5tf 
2MW 
0.13 rad/s 
1.67 Energy

Carbide Railgun I 
1 
6,300m 
3,000m 
2.6s 
1.575x 
4tf 
2MW 
0.13 rad/s 
1.59 Energy

'Scout' I Accelerator Cannon 
2 
6,600m 
3,000m 
2.6s 
1.65x 
4tf 
2MW 
0.13 rad/s 
1.5 Energy

Compressed Coil Gun I 
3 
6,900m 
3,000m 
2.6s 
1.725x 
4tf 
2MW 
0.13 rad/s 
1.42 Energy

Prototype I Gauss Gun 
4 
7,200m 
3,000m 
2.6s 
1.8x 
4tf 
2MW 
0.13 rad/s 
1.34 Energy

Gatling Rail II 
5 
7,200m 
3,000m 
2.6s 
1.8x 
6tf 
2MW 
0.13 rad/s 
1.67 Energy

125mm
Can load up to 80 smallsized hybrid charges.
Name 
Meta 
Optimal Range 
Accuracy Falloff 
Rate of Fire 
Damage Modifier 
CPU Usage 
Powergrid Usage 
Tracking Speed 
Activation Cost

Railgun I 
0 
9,000m 
5,000m 
3.25s 
2.0x 
15tf 
7MW 
0.085 rad/s 
2.15 Energy

Carbide Railgun I 
1 
9,450m 
5,000m 
3.25s 
2.1x 
12tf 
7MW 
0.085 rad/s 
2.04 Energy

'Scout' I Accelerator Cannon 
2 
9,900m 
5,000m 
3.25s 
2.2x 
13tf 
7MW 
0.085 rad/s 
1.93 Energy

Compressed Coil Gun I 
3 
10,000m 
5,000m 
3.25s 
2.3x 
14tf 
7MW 
0.085 rad/s 
1.83 Energy

Prototype I Gauss Gun 
4 
11,000m 
5,000m 
3.25s 
2.4x 
12tf 
7MW 
0.085 rad/s 
1.72 Energy

Railgun II 
5 
11,000m 
5,000m 
3.25s 
2.4x 
17tf 
8MW 
0.085 rad/s 
2.15 Energy

150mm
Can load up to 40 smallsized hybrid charges.
Name 
Meta 
Optimal Range 
Accuracy Falloff 
Rate of Fire 
Damage Modifier 
CPU Usage 
Powergrid Usage 
Tracking Speed 
Activation Cost

Railgun I 
0 
12,000m 
6,000m 
4.25s 
2.75x 
25tf 
10MW 
0.07 rad/s 
3.34 Energy

Carbide Railgun I 
1 
13,000m 
6,000m 
4.25s 
2.8875x 
20tf 
10MW 
0.07 rad/s 
3.17 Energy

'Scout' I Accelerator Cannon 
2 
13,000m 
6,000m 
4.25s 
3.025x 
22tf 
10MW 
0.07 rad/s 
3.0 Energy

Compressed Coil Gun I 
3 
14,000m 
6,000m 
4.25s 
3.1625x 
23tf 
10MW 
0.07 rad/s 
2.84 Energy

Prototype I Gauss Gun 
4 
14,000m 
6,000m 
4.25s 
3.3x 
21tf 
10MW 
0.07 rad/s 
2.67 Energy

Railgun II 
5 
14,000m 
6,000m 
4.25s 
3.3x 
28tf 
11MW 
0.07 rad/s 
3.34 Energy

Cruisersized railguns. (Click link for a more complete list.)
Dual 150mm
Can load up to 160 mediumsized hybrid charges.
Name 
Meta 
Optimal Range 
Accuracy Falloff 
Rate of Fire 
Damage Modifier 
CPU Usage 
Powergrid Usage 
Tracking Speed 
Activation Cost

Railgun I 
0 
12,000m 
6,000m 
3.9s 
1.5x 
32tf 
80MW 
0.04 rad/s 
5.00 Energy

Carbide Railgun I 
1 
12,600m 
6,000m 
3.9s 
1.58x 
25tf 
80MW 
0.04 rad/s 
4.75 Energy

'Scout' I Accelerator Cannon 
2 
13,200m 
6,000m 
3.9s 
1.65x 
28tf 
80MW 
0.04 rad/s 
4.5 Energy

Compressed Coil Gun I 
3 
13,800m 
6,000m 
3.9s 
1.73x 
30tf 
80MW 
0.04 rad/s 
4.25 Energy

Prototype I Gauss Gun 
4 
14,400m 
6,000m 
3.9s 
1.8x 
27tf 
80MW 
0.04 rad/s 
4.0 Energy

Railgun II 
5 
14,400m 
6,000m 
3.9s 
1.8x 
35tf 
84MW 
0.04 rad/s 
5.0 Energy

200mm
Can load up to 80 mediumsized hybrid charges.
Name 
Meta 
Optimal Range 
Accuracy Falloff 
Rate of Fire 
Damage Modifier 
CPU Usage 
Powergrid Usage 
Tracking Speed 
Activation Cost

Railgun I 
0 
18,000m 
10,000m 
4.875s 
2.0x 
35tf 
180MW 
0.03 rad/s 
6.45 Energy

Carbide Railgun I 
1 
18,900m 
10,000m 
4.875s 
2.1x 
28tf 
180MW 
0.03 rad/s 
6.13 Energy

'Scout' I Accelerator Cannon 
2 
19,800m 
10,000m 
4.875s 
2.2x 
31tf 
180MW 
0.03 rad/s 
5.81 Energy

Compressed Coil Gun I 
3 
20,700m 
10,000m 
4.875s 
2.3x 
33tf 
180MW 
0.03 rad/s 
5.48 Energy

Prototype I Gauss Gun 
4 
21,600m 
10,000m 
4.875s 
2.4x 
30tf 
180MW 
0.03 rad/s 
5.16 Energy

Railgun II 
5 
21,600m 
10,000m 
4.875s 
2.4x 
39tf 
189MW 
0.03 rad/s 
6.45 Energy

250mm
Can load up to 40 mediumsized hybrid charges.
Name 
Meta 
Optimal Range 
Accuracy Falloff 
Rate of Fire 
Damage Modifier 
CPU Usage 
Powergrid Usage 
Tracking Speed 
Activation Cost

Railgun I 
0 
24,000m 
12,000m 
6.38s 
2.75x 
40tf 
225MW 
0.023 rad/s 
10.0 Energy

Carbide Railgun I 
1 
25,000m 
12,000m 
6.38s 
2.8875x 
32tf 
225MW 
0.023 rad/s 
9.5 Energy

'Scout' I Accelerator Cannon 
2 
26,000m 
12,000m 
6.38s 
3.025x 
36tf 
225MW 
0.023 rad/s 
9.0 Energy

Compressed Coil Gun I 
3 
28,000m 
12,000m 
6.38s 
3.1625x 
38tf 
225MW 
0.023 rad/s 
8.5 Energy

Prototype I Gauss Gun 
4 
29,000m 
12,000m 
6.38s 
3.3x 
34tf 
225MW 
0.023 rad/s 
8.0 Energy

Railgun II 
5 
29,000m 
12,000m 
6.38s 
3.3x 
44tf 
236MW 
0.023 rad/s 
10.0 Energy

Battleshipsized railguns. (Click link for a more complete list.)
Dual 250mm
Name 
Meta 
Optimal Range 
Accuracy Falloff 
Rate of Fire 
Damage Modifier 
CPU Usage 
Powergrid Usage 
Tracking Speed 
Activation Cost

Railgun I 
0 
24,000m 
12,000m 
5.85s 
1.5x 
55tf 
1250MW 
0.0175 rad/s 
15.0 Energy

Carbide Railgun I 
1 
25,000m 
12,000m 
5.85s 
1.575x 
44tf 
1250MW 
0.0175 rad/s 
14.25 Energy

'Scout' I Accelerator Cannon 
2 
26,000m 
12,000m 
5.85s 
1.65x 
49tf 
1250MW 
0.0175 rad/s 
13.5 Energy

Compressed Coil Gun I 
3 
28,000m 
12,000m 
5.85s 
1.725x 
52tf 
1250MW 
0.0175 rad/s 
12.75 Energy

Prototype I Gauss Gun 
4 
29,000m 
12,000m 
5.85s 
1.8x 
46tf 
1250MW 
0.0175 rad/s 
12.0 Energy

Railgun II 
5 
29,000m 
12,000m 
5.85s 
1.8x 
61tf 
1313MW 
0.0175 rad/s 
15.0 Energy

350mm
Name 
Meta 
Optimal Range 
Accuracy Falloff 
Rate of Fire 
Damage Modifier 
CPU Usage 
Powergrid Usage 
Tracking Speed 
Activation Cost

Railgun I 
0 
36,000m 
20,000m 
7.31s 
2.0x 
60tf 
1875MW 
0.01167 rad/s 
22.0 Energy

Carbide Railgun I 
1 
38,000m 
20,000m 
7.31s 
2.1x 
48tf 
1875MW 
0.01167 rad/s 
20.9 Energy

'Scout' I Accelerator Cannon 
2 
40,000m 
20,000m 
7.31s 
2.2x 
54tf 
1875MW 
0.01167 rad/s 
19.8 Energy

Compressed Coil Gun I 
3 
41,000m 
20,000m 
7.31s 
2.3x 
57tf 
1875MW 
0.01167 rad/s 
18.7 Energy

Prototype I Gauss Gun 
4 
43,000m 
20,000m 
7.31s 
2.4x 
51tf 
1875MW 
0.01167 rad/s 
17.6 Energy

Railgun II 
5 
43,000m 
20,000m 
7.31s 
2.4x 
66tf 
1969MW 
0.01167 rad/s 
22.0 Energy

425mm
Name 
Meta 
Optimal Range 
Accuracy Falloff 
Rate of Fire 
Damage Modifier 
CPU Usage 
Powergrid Usage 
Tracking Speed 
Activation Cost

Railgun I 
0 
48,000m 
24,000m 
9.56s 
2.75x 
70tf 
2500MW 
0.009625 rad/s 
30.0 Energy

Carbide Railgun I 
1 
50,000m 
24,000m 
9.56s 
2.8875x 
56tf 
2500MW 
0.009625 rad/s 
28.5 Energy

'Scout' I Accelerator Cannon 
2 
53,000m 
24,000m 
9.56s 
3.025x 
63tf 
2500MW 
0.009625 rad/s 
27.0 Energy

Compressed Coil Gun I 
3 
55,000m 
24,000m 
9.56s 
3.1625x 
66tf 
2500MW 
0.009625 rad/s 
25.5 Energy

Prototype I Gauss Gun 
4 
58,000m 
24,000m 
9.56s 
3.3x 
59tf 
2500MW 
0.009625 rad/s 
24.0 Energy

Railgun II 
5 
58,000m 
24,000m 
9.56s 
3.3x 
77tf 
2625MW 
0.009625 rad/s 
30.0 Energy

Capital/installationsized railgun.
Dual 1000mm
Name 
Meta 
Optimal Range 
Accuracy Falloff 
Rate of Fire 
Damage Modifier 
CPU Usage 
Powergrid Usage 
Tracking Speed 
Activation Cost

Railgun I 
0 
96,000m 
48,000m 
14.35s 
5.5x 
120tf 
125,000MW 
0.0019 rad/s 
272 Energy
