Well, 105 degrees does approach the hot side of the equation, I'll give you that. (But it's a dry heat, right?
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At the Web Shooters "SECRET in the Heat" last year, participation was down a bit at the dez shooting spot in the Barstow area. I doubt it hit 100, though my memory isn't as good as it used to be. I don't recall much of a wind, though there was a slight breeze that seemed to take some of the edge off the temps.
It was warm enough to cause the rubber portion of the Hogue free-float tube on my Colt to shift a bit. On the plus side, I got to work on my tan--no covered shooting bays or trees or even bushes to hide under.
If it's the desert, facing similar conditions, just drink lots of water and let your aptitude for dealing with heat guide you. I'm sure there are a few here (especially from the AZ or NV or NM crowd) who wouldn't hesitate to shoot if it was 110 even. Personally, I'd prefer shooting in 110-degree heat in the dez than in 95-degree heat and 95-percent humidity in, say, OK. YMMV. BTW, good luck to your son and his buddy; bravo!