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Sturgeon

The Cartridge Collecting Thread

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6 hours ago, Collimatrix said:

 

Very aerodynamic bullet made of aluminum with a brass jacket to increase moment of inertia.  Used early in CETME development.  Kraut space magic but made in Spain.

 

The CSP-004 bullet in that photo is actually lead-cored with a plastic tip, in a gilding metal jacket (as they all had).

 

Voss, the guy who designed those bullets, was one of the early pioneers of very low drag small arms projectile designs, and his work was on the bleeding edge of the knowledge of supersonic drag characteristics at the time. Of course, a proper aerospace type would say something like "so what? bullets are perfectly radially symmetrical", but that's another thing.

 

The goal was to produce a round that had recoil characteristics similar to 7.92x33, but 1,000 yard range like 7.92x57 or (later) 7.62 NATO. The project was unsuccessful basically due to NATO standardization (which the Spaniards weren't a part of at the time, but decided to buy into anyway). The end result of this research was a unique 7.62 NATO loading (which I still don't have! despite it being rather common by cartridge collecting standards) which (unlike CSP-004 there) fit inside the standard NATO envelope but fired a decidedly non-NATO spec 113gr low drag bullet at about 2,600 ft/s. Compare the projectile shape of these rounds with the M80 Ball in the last image in my post above:

 

24770.jpg

 

This ammunition was actually issued with the CETME Modelo B rifle, and produced for a number of years until phased out in favor of full power 7.62 NATO.

 

cetme_b30.jpg
 

I went off memory for this whole post, so it's possible there are some small errors. Effort lol.

 

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I just checked Full Circle.  Sturgeon's account is basically correct.

 

After WWII, the Soviets and Americans fought over all the German jet engine experts and rocket scientists, and the French got all the German tank and gun experts.  For a period in the late 1940s and 1950s all the French tank designs look sort of like panthers and tigers and all of their rifle designs look sort of like STG-45s, and that's why.  As soon as these German scientists weren't forced to wear collars and leashes (early 1950s), most of them moved to Spain where they found the Mediterranean climate and oppressive Fascist dictatorship more to their liking.

 

One of these German scientists was a Dr-Ing Gunther Voss, who was extremely well-informed on the then brand-spanking-new science of supersonic fluid dynamics.  As you may recall, supersonic fluid dynamics were a big problem during WWII because nobody really knew how they worked.  A lot of pilots were lost in dives when their flight controls mysteriously locked up, since the engineers didn't yet understand how localized supersonic flow could cause a loss of elevator effectiveness.

 

So, prior to some time in the 1950s, bullets were basically designed by trial and error.  Gunther Voss was one of the first to scientifically design a bullet for maximum supersonic efficiency.  He developed four super-skinny, lightweight, high-efficiency bullets for CETME from the early to late 1950s.  They were:

CA-001, 8mm 108 grain bullet with an exposed aluminum core and gilding metal jacket.

CAP--01, 8mm, 200 grain bullet with a mostly lead-antimony core, and aluminum tip concealed under gilding metal jacket.

 

CA-002, .30 caliber, basically the same as CA-001, but in .30 cal instead of 8mm.

 

CSP-003, .30 caliber, 112 grains, lead and plastic with fully enclosing copper jacket.

CSP-004 isn't in Full Circle, so I'm assuming it's something that Sturgeon made up, just like the form 4473.

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9 hours ago, Collimatrix said:

So, prior to some time in the 1950s, bullets were basically designed by trial and error.

 

In many cases yes, but people did try to design them mathematically, it's just that their mathematics for that sort of thing sucked ass. S Patrone was designed mathematically, for example, using a Newtonian flow model!

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3 hours ago, Sturgeon said:

 

In many cases yes, but people did try to design them mathematically, it's just that their mathematics for that sort of thing sucked ass. S Patrone was designed mathematically, for example, using a Newtonian flow model!

Probably because they require solving PDEs and solving PDEs is only really feasible with modern computers.

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2 hours ago, Oedipus Wreckx-n-Effect said:

Probably because they require solving PDEs and solving PDEs is only really feasible with modern computers.

 

You can get there empirically, but until the 1930s-1940s there was really no way to accurately measure a supersonic bullet in flight. So for some time, nobody could prove the Newtonian model was wrong.

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They hadn't even figured out how to properly scale wing tunnel data back then (eg, the idea that full scale wings on the P-51 could have laminar flow), so messing up bullet design is understandable (much easier to fit measuring equipment on a plane!)

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3 hours ago, Xlucine said:

They hadn't even figured out how to properly scale wing tunnel data back then (eg, the idea that full scale wings on the P-51 could have laminar flow), so messing up bullet design is understandable (much easier to fit measuring equipment on a plane!)

 

I thought the lack of laminar flow on laminar flow wings was an issue of imperfections in the surface finish like rivets, dents and bugs, and not an issue of scaling.

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15 hours ago, Collimatrix said:

 

I thought the lack of laminar flow on laminar flow wings was an issue of imperfections in the surface finish like rivets, dents and bugs, and not an issue of scaling.

 

In the absence of any surface defects, the transition from laminar to turbulent flow will occur on the outer edge of the boundary layer and propagate inwards to the surface of the aircraft. My fluid lecturer says this occurs at about Re = 5E5, which for an aircraft at 100m/s (~200 knots), and assuming air density of 1.229 kg/m^3 and dynamic viscosity of 1.73E-5, will occur about 7cm in from the leading edge. This is for sea level which is admittedly not representative of most flight, so using the data here this is how the length of the laminar region varies with altitude

qhsV4tS.png

It gets up to a bit over a foot at high altitude, but is still well below the P-51 chord length (scaling off a 1:76 model I have lying around, ~1.3m at the tip)

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