Re: Rogue One Felicity Jones gun - ideas
I am sorry if this is long and boring. This may be more than anyone wants but I would first like to calibrate our terminology. Then we can understand what moves, what doesn’t and where we need to be concerned about providing clearance for the movement.
First I am sorry I did not include some of my assumptions about the shroud in earlier discussions. One reason I was so interested in what I have been calling the “rail system” was to understand the attachment points for the shroud as it had to be attached to the weapon’s frame. Since the side brackets already were attached to the frame I was interested in how they might also integrate with the shroud. I think we now see from the toy illustrations the bracket is one piece which wraps over the top and it is also either a part of, or attaches to, the shroud.
Here are some terms and some mechanics. The barrel is attached at the rear to the barrel extension, which is also called the receiver in Luger terms. The receiver is cylindrical at the front where the barrel screws in but behind that point the receiver has parallel left and right “walls” but no top, bottom or rear. Between the walls of the receiver there are a number of parts the most important being the firing pin at the rear and the breechblock at the front. Overtop the firing pin are several parts and linkages which are attached to the breechblock at the front and the frame at the rear. I will lump these together as the toggle.
The frame is the stationary part of the weapon which some here have called the lower receiver. Lower receiver is a term used with the AR-15 family. The lower receiver there and the frame here, holds the trigger assembly, magazine, handgrip, etc. so the term is probably well understood by many people. When a cartridge (or airsoft pellet) is fired, escaping gases first blow back the breechblock. The block stays completely inside the receiver so no additional clearance above the receiver is required for the breechblock movement. However as the breechblock moves rearward the linkages drive the toggle rearward as well. The center toggle link and the rear toggle link act as a hinge and at the point of connection these two links hinge upward giving the traditional blow-back look provided in the earlier .gif.
The rear toggle is also connected to the frame. Since the rear of the toggle is fixed, the amount of rearward movement of everything is restricted. Partway through the rearward movement of the breechblock and toggle, the barrel and barrel extension (receiver) also move rearward, but not as much, and like the breechblock only in a linear fashion. Again no additional top clearance is required for the barrel or barrel extension. (The purpose of this movement is to eject the spent casing and prepare to receive a new cartridge). A the end of the travel, springs drive all of the same parts forward again, stripping a new cartridge from the magazine, pushing it into the chamber, setting the firing pin, locking the breechblock and all is prepared to fire another round.
Now that we know what moves, we can look at the required clearances.
The highest point of the barrel/barrel extension (disregarding the front sight) is where the receiver meets the barrel; this point is also the most forward part of the frame. This is also the point where the bottom half of the shroud is cut away. The width of the frame at this point is 1.125” which is one of the points of confirmation I used after calculating the shroud diameter based on other reference points. Anything smaller than 1.125” and the inside walls of the tube would rub against the sides of the barrel/barrel extension. Even with the outside diameter as 1.125, the walls must be thin.
The highest point of the breechblock is the next critical point. At the rear, the block curves upward and rises to a height of a little more than 4 mm above the receiver. I will use 5 mm as a margin of error. This point is at the rear of the trigger side plate when the breechblock is all the way forward and weapon is ready to fire. The distance from the front of the frame to this high point is 50 mm. However because of the breechblock’s sits inside the receiver if top clearance is provided for the receiver, for the first 40 mm of this distance the breechblock will also have clearance. It is only the final 10 mm where additional clearance would be specifically needed for the breechblock. Once this 5 mm clearance is provided this height would be sufficient for the next 33 mm of “at rest” clearance as well. (However once movement starts and the toggle starts to break upward the clearance issues would become more complex but I believe we can avoid those issues here.) It is only when we reach the broad lugs at the hinge point of the toggle where even more clearance would be required.
However I believe the first 40 mm which provides clearance for the both receiver and the front of the breechblock is all we need to use and be concerned about. In my earlier diagram I have the total length of the shroud as 155 mm and had it end at the front edge of the trigger side plate. If this is the point where the bracket wrap-over begins, the width of this could be 15-16 mm and still not interfere with any of the moving parts. I also have about 15 mm of shroud behind my grooved section, so the wrap-over potentially could be as wide as 30 mm and not require any more clearance than what my shroud design provides.
I will rework my diagrams based on the newest information and provide them for comment. In the meantime I hope more discussion ensues as the more inputs and observations the better the final product will be for all.
