6,000 feet, two moving objects, wind.... it's completely unrealistic.
The effective range of gunners in WW2 was about 400-600 yards. Period. Extend that slightly for the sighted and slaved nature of the -29.
Radar guided B-52 tail gun, range was about 1,200-1,600 yards, as a guidepost.
The gunners on the City of Bartlesville scored a kill on a Japanese interceptor over a mile away during a low level daylight raid over Japan. The radar guided fire control system enabled the gunners to hit targets further out since all the aiming and Kentucky windage was all done by computer. Not saying 100% hits all the time but getting hit 2,000yards away wasn't out the realm of possibility. I don't think a manually aimed gun turret like on the B-17 or B-24 would have pulled it off, but with a computerized radar guided fire control system, it was possible.
On a side note, Airman Albert E. Moore serving as the tail gunner on the B-52 "Diamond Lil" shot down a MiG-21 when it locked on the MiG with it's radar 4,000 yards out and destroyed it with his quad .50 caliber machine guns. This was the last time a tail gunner shot down a plane with machine guns. This took place on Christmas Eve, 1972 during the Linebacker raids.
A week earlier, Staff SGT. Sam Turner, detected two MiG-21s approaching his B-52 and locked on the closest one, about a mile away and fired. He couldn't tell from the resulting fireball he saw whether or not he hit the MiG-21 or if it was an errant SAM missile that blew up early. When he looked at his radar, he noticed only one fighter was visible and it was quickly leaving the area. Staff SGT. Sam Turner was awarded the Silver Star for this action.
ack-ack