Wonder of wonders, sometimes things happen top drive home the point. The other day we were working with the cop squadron doing a TRQC shoot. Out of the 15 shooters we had, several of them had dead batteries in their M-68 and guess what, '68 batteries isn't a benchstock item for us at the range. Sorry bud but you are either going to have to use your iron sights or go back to the squadron and explain why you didn't qualify that night to the commander. Some of their performance wasn't that great especially during the night fire portion of the course but by using their iron sights, every one of them managed to qualify.
The last TRQC class we had featured one cop whose BUIS sight was taken off (damaged and waiting on a repair) that tried to fire with just his front sight post during the iron sight portion of the course of fire. Of course the first two stages he didn't have a single hole on the target and finally took our advice to get a different rifle from the armory.
So, what are the lessons learned here? Have a BUIS in the event your optics (be it a '68 or ACOG) goes down. If you don't have a BUIS and your optics can't be used, you ain't gonna hit crap!