slammer,

With Win. factory .223 ammo, it shoots fine for me at 80 degrees, but at 105 degrees about every 3rd round blows its primer. Disregarding all theory, this is first hand experience that tells me heat can have an effect on pressure in ammo. There were reports of Rem factory .416 ammo causing sticky extraction in African summer temps. But Rem has since changed their loading and there are no recent reports of this problem. Some factory .458 win. loadings also suffered from sticky extration. And Weatherby factory ammo has experienced several incidens of stuck cases in African heat.

In a DG situation I prefer to use a load which is well below max pressures just in case. Better safe than sorry.