clark33,
I recall the issues from the past as well. However, recently I have shot the 5.56 versions of the 68 grain and 75 grain Frontier offerings for the last two years and have great results. All of my barrels shoot both the 68 and 75 grain versions well...with no kabooms.
I shot about 800 rounds of the 75 grain offerings in a recent class and several of the other students were shooting the 75 grain Frontier offering too. For clarification, all the examples I know of were shooting the 5.56 version.
BC