Mike Irwin, read the link in my post that explains why the SMLE's were so accurate at the longer ranges. Click on the "PDF" link in the "View the Book" window on the page's left side.
Same thing can happen at short ranges; check out the following:
http://www.varmintal.com/apres.htm
The M14NM competition service rifles did this to a lesser degree due to the gas port's location about mid point in the barrel. One of the service teams learned this testing these rifles for accuracy shooting bullets through chronographs.