Talk:SCMITR

Untitled

I found a .gif of a photograph of a SCITMR shotgun shell, cut open to show the arrangement of razor flechettes inside the plastic sleeve (sort of a sabot) inside the cartridge.

If any registered user is interested, I can email it to you and you can put it on the page.

Do you have any source information on the image? I can find pictures on the web, but those may be subject to copyright. If you can show the picture is from the CAWS data published by the US government, then the image is public domain, and it can be used here. As I recall, pictures of pictures are not copyrightable (see Wikipedia:Public_domain#Uncreative_works), so any scan made of the CAWS data is not copyrightable, and can be used. scot 15:19, 10 January 2006 (UTC)

Unfortunately I have no idea of its origin, nor do I know who, if anyone, owns the rights to the image.

pictures

[1]

The picture here says 20 gua right on it, every other picture I've seen was based on that one, with the 20 edited out..

Hmmm, that is odd. The CAWS guns were all based on 12 gauge derivatives; in the case of H&K, for example, a 19.5 x 76mm belted case, equilvalent to a 3" 12 guage shell[2]. The AAI is variously listed as "special 12 guage round", "20 mm", and "18.5 x 79 mm". 18.5 mm (.729) is the bore diameter of a shotgun, so 20mm might well refer to the outside diameter of the shell--I can't find a dimensioned drawing of a standard 12 gauge, so I don't know how big they are. The 20 ga. round was probably a test bed for the SCIMTR projectile; certainly firing, say, 5 or 6 of them from a 20 gauge (look at the picture of the sabot closely, and you'll see that it seems unlikely that 8 of them are present) would give you just as good a terminal ballistics testing as 8 from a 12 gauge, and with far less recoil to deal with. Since a big issue was penetration of armor at long ranges, and since hitting a small sample of armor at long rage was going to be a matter of chance given the spread at that range, a low velocity load fired at short range to give you the same terminal ballistics as a high velocity load at long range would also be helpful in testing. Purely speculation there, but it does seem a logical way to explain why a 20 gauge round would be associated with what were well documented 12 gauge guns... scot 15:38, 30 October 2006 (UTC)

Spelling? Acronym?

I see SCIMTR, SCMITR, and SCITMR between the article and the talk. What is the correct spelling? Obviously it's a play on scimitar, so it should be either SCIMTR or SCMITR, but which? It looks as if it should be an acronym; what does it stand for? Hieronymus Illinensis (talk) 04:02, 16 July 2008 (UTC)

Bent fins were not for spin.

Spin is very unstable for long, thin projectiles. Flechettes, darts, arrows, and rockets are stabilized by aerodynamic drag.

The fin bends were exactly parallel to the centerline of the flechette. They don't cause spin, they just prevent it from tumbling in the plane of the blade.

--Rick MILLER (talk) 19:17, 3 October 2008 (UTC)

I'm not sure there's really enough data available on the SCMITR to make the claim either way. I can, however, provide at least one solid counterexample to your claim, and some arguments against the characterization of "drag stabilization". The Hale rocket, which has a length to width ratio of 9.5:1, and is stabilized entirely by spin induced by biased vanes in the rocket exhaust. This is a much greater length/width ratio than the roughly 4:1 or 5:1 ratio of the 80 grain ultra-low drag .223 caliber bullets. Let's do a quick thought experiment on another example, the arrow. Most arrows are provided with biased fletching, to induce spin. This is not strictly necessary, as, unlike the 2-fin SCMITR, the 3 fletchings provide stability across all axes. So why add a bias? Consider the case of an arrow with non-biased fletching. As it flies coaxially with its path, the fletchings, which are at a zero angle of attack, provide almost no stability, because they produce only a tiny drag force. Alter the angle of attack, however, and the fins generate a significant amount of lift, which forces the rear of the arrow back into coaxial alignment. It is this lift, NOT the drag, which provides the stability to finned projectiles; replace the fins with thin cylinders that provide the same drag, and the projectile is no longer stable.

Now this finned arrow is somewhat stable, but since it uses a negative feedback situation, it isn't perfect; it will oscillate around the coaxial orientation, but since the centering force drops to zero it will always "wander" around the stable state, never quite staying there. However, with the bias, the arrow starts to spin until the fins are, once again, at a zero angle of attack to the airflow. We're back to the state of the original non-biased, finned arrow, but now we have some additional stability provided by the spin. The spin is not nearly enough to fully stabilize the 100:1 length to width ratio of the arrow in the face of significant yaw forces, but it IS enough to get it to "settle" better in the coaxial state. The arrow will fly straighter, and with less wobble than one with non-biased fletching, which is precisely why most arrows have had biased fletching. The question is, do you consider that case primarily spin stabilized, or primarily aerodynamically stabilized? The spin is providing stability most of the time, but it's insufficient to handle anything by the smallest yawing forces; the fins provide stability in the worst case scenarios, but those only happen intermittently, when yaw forces exceed the ability of the spin to counter them.

Unfortunately, the information on the SCMTIR is very sparse, and there is no other similar case I'm aware of that would let us decouple the stability provided by spin versus the stability provided by the fins. Given that I'm working from a machine translation of Finnish to English, I'll go ahead and alter the wording to avoid making an unprovable claim. 21:49, 3 October 2008 (UTC)