By the time they got to the D-model, they had a test stand where the plane was still on its gear (3-point) and the wing LE was nudged up to a set of curved chutes on a movable rig. The chutes had a slow 90 degree bend with some traps/suppressors/heat exchangers(?) on the end. The slugs went down the chutes into a collector box. I'm not sure if/how this allowed boresighting or if it was a prelimary weapon check only. As fast as they were building the things, I'd bet they combined the functional check with boresight. No time to do essentially the same setup twice. And the picture--shows testing going on at night in Inglewood, which is a couple blocks down the street from me. Noisy times.....