reading values from an IR receiver in a laser tag gun
You should look at the output signal of the IR receiver. It is not likely to be an analogue voltage. Instead expect it to be a modulated digital signal which you will have to decode in your MCU software. The 38 kHz typically used for IR communications is the carrier frequency of the IR signal. The transmitter will send a signal by sending bursts of IR light at 38 kHz. When the bursts are coming it means one logic level say a '1'. When transmitter holds back on the bursts and there is no light coming to the receiver that would be the opposite logic level say '0'. Note that the modulated '1's and '0's typically will persist for multiple cycles of the 38 kHz. The IR receiver strips away the 38 kHz bursts and outputs a waveform the follows the modulation signal. A typical IR protocol is setup to transmit about 10 times per second.

The best way to get a handle on the actual signal is to look at it with an oscilloscope. Alternately you can use a timer in an MCU to measure the interval between each sequence of low to high transition and high to low transition in the IR protocol transmission and store the measurements for later inspection. A simple setup could take the readings and then send it out a serial port to a PC for study.