Michael,
Many variations occurred, once you had finished the ALL ARMS SNIPER Course to suit the individual, but I have to say none were a serious deviation from the norm.
In terms of wanting ideas surrounding the actual shooting not camouflage, these relate primarily to the use of a well fitted sling and your hold of the rifle using that as an aid.
Parachute Regiment snipers were issued with smocks minus the sling clips as it was these very same smocks that were used to parachute in on operations and the clips if retained in the normal issue ones would snag rigging lines.
My label in my old smock says simply SNIPERS DPM but it is a PARA issue and as rare as rocking horse poo, as only 100 were made for Military Parachutists and I was lucky.
In short it was the selection of the right sling which proved the best solution and I always preferred the SEYNTEX Belgiumfibre sling issued but we did also get the leather 1907 one from the USA
as well.
Hope that helps