The first shot occurring earlier than the WC originally thought makes a lot of sense to me. So I began looking for visual evidence of this shot around the likely time of Z160. Also, the following tends to indicate the shot took place even earlier than Z160:
1.) Howard Brennan's affidavit of 11/22/63 that states JFK's back was inline with the last window (west) of the south side of the TSBD when the first shot sounded.
2.) The interesting work of Max Holland, which is described in this well written article by Kenneth R. Scearce:
http://mcadams.posc.mu.edu/scearce.htm The above article includes some well done clips of the Zapruder film.
3.) This Willis Lamm article is interesting also:
http://www.kbrhorse.net/signals/eagle03a.htm4.) The action of D.V. Harkness , the traffic cop assigned to the intersection of Main and Houston. From the first time I saw the Hughes film clip, many years ago, I wondered what had caused Harkness to suddenly turn away from his primary duty of the
control of the intersection and walk towards where the limousine was traveling while apparently looking very intently for something. And whether he had just heard the sound of the first shot. If so, his actions would fit what I might expect.
5.) The more I considered this, the more convinced I am that the fraction of a second stop/start of Hughes' camera is highly unusual and therefore it could be a startle reaction to the sound of the first shot. I checked Dale Meyers' synchronization report of the films and he reports that there are six frames missing due to this stop/start. There are other items of evidence to support this theory. The image below will illustrate some of what I am going to write:
As illustrated above, the Tina Towner film ends just barely before the Hughes Film split-second break. Tina has said that the first shot occured just after she stopped filming. At essentially the same time as the Hughes film split second break, the Dorman film shows one extremely blurred frame, which I believe indicates a sudden jerk (startle reaction to the first shot) before stopping for 49 frames.
Brennan's first shot description in the 11/22/63 affidavit, the films' anomalies, and the Harkness reaction all happen just before the Zapruder film begins. Also Rosemary Willis already has her head turned sharply, looking back over her right shoulder in the direction of the TSBD, in frame Z133, the first frame of that sequence. She has said she turned her head to look back there when she heard the first shot.
Based on the above, when I created the 3D mock-up of the sniper's nest, out of curiosity, I located the limo in line with Brennan's position and the last windows of the south face of the TSBD. I wanted to see if the sniper had a good view of JFK at that point in time, he did. I have always thought that even if the sniper missed, this shot should have at least hit the limo somewhere. What became apparent to me is that if the sniper took the first shot at that point while tracking the target from his left to right, the small box is in the way of the rifle. It appears to me that the likely reason the first shot missed is that the rifle was stopped by colliding with the box, but the target kept moving. So the bullet would have hit behind the limo on the road. Here are some images to illustrate what I am saying:
The three limos represent it's locations at: shot #1 (just before Z133), shot #2 (at Z225), and shot #3 (at Z313). You can see Brennan's location on top of the fence. The other two men represent Dillard's positions at his two photos immediately after the shots. They also give an idea of the path of the vehicles in the motorcade. I used elevations and measurements of distances from Roberdeau's map. And photos of the sniper's nest. The elevation of the sniper's eyes is 36 inches, this corresponds with my own eyes when sitting on a box the same height as the one the sniper sat on. I am roughly the same height as Oswald.
I encourage others to make their own mock ups of the sniper's nest to see if they end up with something similar to mine and let us know. The program that I am using is free. It is called SweetHome 3D. I think I did have to pay a few bucks for some library items. And I found the rifle for free online. I had to improvise some things. The limo is an example.