I did one of these back in the mid-90s here in PDX. It was held out at a National Guard camp and you had to attend a mandatory safety session the day before.
The 5k was three one-mile loops of a XC course with the .1 added to the end of the final loop. After the first loop, you had to stop 50m before the target range and walk into it, finding an open stall with a .22 caliber target-type rifle there. You loaded the five-shot clip into the rifle and took aim at the salad plate size target 25 meters away, firing in the prone position the first time through. After your 5th shot, you had to walk 50m out of the range before resuming running. The second time through, you shot in the standing position. The clock is running thoughout.
Having always had a keen interest in the winter biathlon, I always wanted to try this event to really see how tough it was, but never lived near xc skiing areas. So when the summer version came along, I jumped at the opportunity to give it a, err, shot.
I already had a lot of experience both running and with target shooting (pistol). In the event I did, for ever target you hit, you got to subtract five seconds from you overall time.
I actually managed to hit 9 out of 10 targets, missing one in the standing position. The thing that got to me the most was not the elevated HR or breathing, although that was tough. It was the sweat running down my face and into my eyes. Next time I would wear a headband or something.
I think my overall time was something like 17:55, including the :45 I got to subtract for hitting nine targets. I loved doing this and wish there were more summer version events around. You could say I had a real blast and got a big bang out of it! Badda-bump. :)