I don't think the diameter is that of a sterling. It's just a feeling. The screen prop looks quite small. It's always my feeling that the prop was made by taking a cast of a sterling (which might have had some shrinkage) and then cut it apart, added the barrel, and rail to make a master. Then that master was used to make the mold in which created the screen used props. So those too could have additional shrinkage. So no, I do not think a sterling grip would be accurate for size.
I agree with you that's the most likely way these buggers were made. That would account for the smaller size that Darth Lars reported from the screen used prop. The question is of course how much smaller we're talking about here. If it's a shrinkage of less than 5%, building a DH-17 with E11/Sterling measurements for the trigger housing/grip should be feasible. If it's more than that, it will need to be scratch built.
It's my hope that someday someone will determine the correct size and fabricate the weapon from scratch.
The single point sight appears to have been originals. Their sizes should be possible to use as a reference. Lichtbringer posted these measurements:
I'll assume they are correct. Fiddling around a bit with the screenshot El Loco posted, I get this:
The two lines are just copies of each other. While we can't see the entire receiver due to the troopers hand, the ocular of the sight and receiver seem to be more or less the same diameter. According to Lichtbringers measurements, that gives us a receiver diameter of 35 mm. The Sterling being 38,1 mm, indicating a shrinkage of around 9 %.
I applied the same method to Darth Lars' photo of his cast and original scope, and got this:
This gave me an estimated receiver diameter of 33 mm in front of the scope rail. Perhaps Lars can confirm? This translate to a 13 % decrease in size between this cast and an original Sterling.
Now, my methodology is severely lacking, and the source material (screen shots) is skimpy. Still, with a bit of goodwill, it's possible to correlate what I have found with Mara Jade's Father's theory of how these blasters came about, if we assume each casting reduces the size with a smidge above 4,3 percent. If so, an original Sterling would have been cast, the cast modified and cast again producing the screen props at about 8,5 % reduced size. Taking a cast again would reduce it to just above 13%, like Lars' cast.
The numbers tally with what Lars said about the original prop being noticeable smaller than a Sterling, and his prop being smaller again. The numbers don't ad up perfectly, but my methodology is again not perfect. In comparison, both the nerf-blaster and the Master Replica ones have more or less the same receiver diameter as an original Sterling.
It may be another generation of casting between the cast screen prop and what Lars has, but it might have happened in recent time with more modern material that did not reduce size.
All in all, I would say the original screen prop probably is between 8 and 9 percent smaller than an original Sterling. I'd also like to say Darth Lars has a
really sharp eye for scale!