Manually start the tcp server by clicking "Start Recoil Server" on the recoil outputs tab.

Or select the checkbox to autostart on load or start the .exe with tcpserver parameter to autostart tcp server:
Lightgun.exe tcpserver

Commands are sent as a single message, you can't merge 2 commands in one message.

IMPORTANT
Each message starts with either 1,2 or B.  1 is Player1, 2 is Player2, B is Both lightguns.

Then follow with:

A - Fire Single Recoil
B - Start repeat recoil
C - Stop repeat recoil

D - Set to single shot recoil mode
E - Set to repeat recoil mode
F - Set to mixed recoil mode

G - Set to "Automatic Default" preset
H - Set to "Automatic Fast" preset
I - Set to "Automatic Strong" preset

These require a 0 or 1 after to enable/disable
J - Enable/Disable Recoil
K - Enable/Disable Trigger recoil
L - Enable/Disable Pump Action On event recoil
M - Enable/Disable Pump Action Off event recoil

These require a value added after
N - Set single shot recoil strength 0-10
P - Set Automatic pulse length (strength) 40-80
Q - Set Automatic delay between pulses (speed) 0-50
R - Set Automatic delay after first pulse (gives mixed functionality) 0-16
T - Fire a pulse, 0-9 = number of shots, 0-999 delay in between in ms
U - Fire a soft single recoil, 0-10 = strength

S - Reset to setting that are on the form

When using forced firing that will clash with trigger firing, so you need to disable 
trigger recoil before manually forcing recoil events.

Pulse can be used to do a reloading shotgun style cocking, like this T2200.  It can also be good for a character death like T4100.

If you are out of ammo, firing a softer single shot replicates an empty chamber like this U5.

The recoil communication does appear to be fast enough so that you can send realtime recoil events, so if you are connecting a game to the Lightgun, rather than utilise the fact the trigger will fire recoil, you can actually send the fire recoil event over TCP and it responds quick
enough.

You can test sending commands in the text box in the recoil outputs tab.