Laser Beam

I can't provide a parts list, but perhaps you should look at simple IR controls like TVs and VCRs have been using for years. The only difference, is instead of using omnidirectional IR LEDs, you will be using a directional laser (Or perhaps IR and optics to focus the beam).
Each receiver will need to be programmed to associate a 'command' with the 'mode' you want to use... ie, a couple rapid pulses and the gun knows it's been requested to fire in rapid-fire.
I would suggest against 'reprogramming' the gun in this way. Simply tell it to use mode 1, 2, 3, 4, etc... and what each mode does.

 

You just need an LDR and a PIC chip.

 

Doesn't a "PIC" chip need some kind of circuit, or circuit board?

 

Waveshare Laser Receiver Module Laser Sensor Module Transmitter Module

First it says: Receiver Module then Transmitter Module ??

 

Colin, it's a POS laser-pointer diode emitter mounted next to a photo-sensor (both unspecified) with a lens. It is intended to be used as a reflective "trip wire" sensor, reflector also unspecified. That's why the "range" is so short. It would probably work at longer distances if you could reflect the laser pointer back into the lens with a flat mirror.

 

I'm sure you could make it work... but I wouldn't bother with it.

Food for thought, you will NEED to be able to tell the difference between a laser and normal light. If you are using these outside, it may be difficult due to the power of the sun... That is why most IR stuff is 'modulated'. It's not just 4 simple flashes... It flashes at a specific frequency.

Anyway, you only need a detector. I would urge you to ignore Colin's comment about the LDR... They tend to have a slow response... This would be ok if the signal you send is slow enough, or if you have the time to hold the gun in-line with the laser long enough for the program to load.
Using a photodiode or photo-transistor is quicker and would be ideal for this application, but you still need to do your best to make sure that only the laser light triggers is. (This is largely why IR is used... as it's easy to filter out IR from other light sources to prevent interference and false positives.)

 

Oh hey, think about making some kind of system whereby the fully-auto setting skips every few shots to simulate lowered accuracy, or if it's a damage or point based game, make the single shot mode give more damage\points. Otherwise, why would anyone not use the fully-auto mode? Unless every gun will only have a fully-auto mode or you just want the advantage. Ha! It is your game after all!