Thanks for the inquiry, and thanks for visiting the site. (sorry, I'm just seeing this now).
First and foremost, I keep the website devoid of info for legal concerns.
People seem to either know what they want, or ask questions.
Secondly, I'm just a novice thrower and maker, and there is a lot of contraversy and disagreement on the subject (especially regarding the Asian schools and styles). The 528 shuriken is the only piece that I currently sell that I have personally designed. Of course, I can tell you what my intentions were.
Similarly, I am in close contact with Houzan Suzuki (designer of the Mumyou-Ryu wares), and our buddy Ralph Thorn (designer of Shur-knife). So I can tell you a good bit about their throwers.
However, the other items are based on traditional Japanese designs. I can't tell you what the original design considerations were, but I can tell you how one design compares to another in terms of performance.
We did/do plan on making an informational website called WAWT.org (site is up, but blank). WAWT (world association of weapon throwers) is a concepts spawned by Ralph Thorn and his buddies. So far the project has been tied up in red tape.
Here is the outline that I made:
http://docs.google.com/Doc?docid=dd6fz4zq_43dxjkpnhm&hl=en
Anyway, I appreciate your inquiry and I agree with you - there should be an informational resource.
I'll work on writing up an overview, and I'll post a link here. In the meantime, here are the answers to your specific questions:
- regarding profile shape (square, round, hex), I would say that square requires one kind of grip, while hex and round require a slightly different grip. The difference is not that critical. A knife grip, however, is a bit different.
- the "model with the fatter front" is the 813, I believe. This is a 'copy' of the traditional Negishi-Ryu shuriken. The fatter front, as you said, moves the center-of-gravity (COG) towards the tip.
-the "shuriken with a hole" is drilled-out to a depth of 2". This also moves the COG towards the tip. Houzan designed this as a modern-day version of the Negishi-Ryu concept.
-to understand the effect of COG position, you need to understand the grip. The basic shuriken/Ralph Thorn grip has the butt of the weapon in the palm (somewhere), while the fingertip (or tips) rest on the shaft. Generally, the fingertip propels the weapon.
The trajectory of the weapon, as it relates to COG, boils down to the relation of the COG to the fingertip. Since the distance from the cradle of your palm to your fingertip is fixed (within an inch or two), what we're really talking about is the distance from the butt of the weapon to it's COG.
In other words, lets say I have two shuriken with the same mass:
8" long, with a COG 5" from butt
14" long, with a COG 5" from butt
then IN THEORY these two will fly the same.
In Mumyou-Ryu and Ralph Thorn's style, it is preferred to have the COG at the fingertip. Note that the "Long Shuriken" (like the 528) does not have any COG-modifying features (other than the tip grind). At 12" long, its COG rests at the fingertip. By the same logic, a 16" shuriken would have to be handle-heavy (like the Shur-knives).
Of course, everything changes if you change your grip, or your throwing style (traditional Japanese techniques use a sliding release, which imparts a back-spin on the shuriken).