That name of game, particularly when it comes to semi-auto firearms is “gas control.” When we were using semi-autos with 20-inch barrels, as were standard on the original AR-15s, a simple flash hider/compensator, such as the ubiquitous “birdcage” design worked just fine. The split brake on the front of the XM16E1, despite being decried by troops in the jungle for catching on vines, actually worked very well. Gene Stoner and his team were smart guys.