"Big Bunco" and "Big Elevator" would have been recorded the same day. In "Big Bunco," a new partner was introduced for "Sergeant Friday," a tall, red-headed kid, as was described by "Friday." The story was that Friday's regular partner, "Ed Jacobs," was being loaned to the Police Academy as an instructor. "Big Gamble" would have been recorded the same day as episode #151, "Big Safe."  Milner, however, did not appear in "Big Safe."  It was explained at the beginning of the episode that "Bill Lockwood" was home with a badly sprained ankle and couldn't make it to work. The very next episode after "Big Gamble" was entitled "Big Mail."   Herb Ellis played Friday's partner, "Frank Smith," in that episode. There was no explanation as to what happened to "Lockwood."  

Milner was not found in the 20 episodes which followed "Big Gamble" -- either in the beginnings (where "Friday" said who his partner was for that episode) or in the endings (where the credits were given in all but 5 of the 20 episodes). Milner was not listed in the credits, and "Lockwood" was not the partner named. Relying upon information provided by "Jerry Haendiges Vintage Radio Logs" (http://otrsite.com/logs/logd1005.htm) in addition to listening to episodes at the website (http://www.archive.org/details/Dragnet_OTR), it can only be determined with certainty at this point that Milner was in the three episodes listed.  More research is needed.