Sound Noise
Level
(dB) Effect
Jet engine (near) 140
Firecracker 140
Gun firing 140
Rock concert 110-140
Boom box 120 Threshold of pain (125 db).
Thunderclap (near) 120
Stereo (over 100 watts) 110-125
Chainsaw 110
Jackhammer 110
Snowmobile 105
Airplane (near) 103
Garbage truck 100 Regular exposure of more than 1 minute risks permanent hearing loss (above 100 db).
Farm tractor 98
Motorcycle (near) 90 No more than 15 minutes of unprotected exposure recommended.
Subway 88
Lawnmower 85-90 Level at which hearing damage begins (85 db).
Television 70-90
City traffic noise 80 Level at which constant exposure may cause hearing damage.
Alarm Clock 80
Washing machine 78
Dishwasher 75 Long exposure to sounds less than 75 db is unlikely to harm ears
Vacuum cleaner 70
Hair dryer 70
Laughter 60-65
Normal conversation 50-65
Refrigerator humming 40
Quiet room 40
Whisper 30
Rustling leaves 20
OK those are some normal everyday sounds here are some airsoft pistols loudness
Springer - TM S&W PC356 84dB
Maruzen S&W M4506 88dB
Marushin Bren Ten 8mm 86dB
Tanaka S&W M29 6.5" 84dB
KSC H&K Mk23 SOCOM 94dB (86dB with silencer)
Western Arms SV Infinity Ltd 6" 96dB
Western Arms Beretta Cougar 8045 96dB
S&W Performance Center M945 94dB
KSC M93R II 94dB
So I personally dont think it was teh loudness of the pistol but when the gun was fired he was near the ports that release the air pressure. That in turn ruptured or tore his eardrum. I personally would go get checked out for that possibility. Check out this site it will explain what I mean....
http://www.nlm.nih.gov/medlineplus/ency/article/001038.htmNow I may not be a doctor but going by what you said I did a little investigation and my opinion is to go get checked out.