What Capesam said... The angle you fire at still allows for groove to slide over tongue. And on an exterior, with longer lengths needing some persuasion, you aren't trying for as tight a fit as you would need on a flooring installation. If the wood is really dry and you get some splitting, try backing off the pressure at the compressor, then again you may have to use the punch to set the nails flush. Don't sweat it, you'll be fine by your 4th or 5th board. And keep checking for plumb
before you reach the window or door casings.
IMO the stainless steel products we get today suck. I have some bleeding through on the Azek trimboards around the windows of my own house
