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NGSW Phase 2 Consolidation and info   Small Arms <20mm

Started 30/8/19 by gatnerd; 452481 views.
stancrist

From: stancrist

21/9/21

Reliability of feeding, chambering, extraction with such an extreme L:D, and zero case taper?

smg762

From: smg762

21/9/21

My new thought for a 'ultimate' LMG is something as light as a SAW but with extreme penetration. Either a 6mm unified or a saboted 4.5mm with the same energy.

Could the CT arrangement allow for a more extreme AR2 shape?

The KEC sounds good. Am i right in thinking a slam and go gun, means that you can literally jam in a belt box without messing around with links?

And does anyone have opinions on the Ares shrike style of 'dual feed'.....both belts and mags in one light package

  • Edited 21 September 2021 15:13  by  smg762
VPMudde

From: VPMudde

21/9/21

I've been ruminating on the supposed 6.8mm magnum projectiles and their trajectories.

The following is an estimate for the projectile made from images available online

5 caliber bullet, 2.5 cal nose cone, 0.1 cal meplat, 0.8 cal 7° boat tail, secant ogive radius = 2x tangent ogive radius.

With a density of 8.5 g/cm3 (Pb-free EPR) it comes in at 123.7 gr. Seems a little light, in light of the supposed 135 gr bullet weight. Even solid copper in this shape only comes in at 129.5 gr.

Does that mean that the 135 gr figure is only for the AP variant (due to the use of tungsten)? And that the GP projectile is actually a fair bit lighter than AP? Or am I wrong about this shape? 

Now I know this tool is a bit generous with BC at times, but considering that this bullet isn't 135gr yet I'll take the 0.26 G7. At 915m/s it's not a bad trajectory at all. 1 second to 700m,  800+ joules out to 900m, supersonic out to over 1100m. 

EmericD

From: EmericD

21/9/21

VPMudde said:

5 caliber bullet, 2.5 cal nose cone, 0.1 cal meplat, 0.8 cal 7° boat tail, secant ogive radius = 2x tangent ogive radius. With a density of 8.5 g/cm3 (Pb-free EPR) it comes in at 123.7 gr. Seems a little light, in light of the supposed 135 gr bullet weight. Even solid copper in this shape only comes in at 129.5 gr. Does that mean that the 135 gr figure is only for the AP variant (due to the use of tungsten)? And that the GP projectile is actually a fair bit lighter than AP? Or am I wrong about this shape? 

The bullet is longer (L/D ~5.15) with a slender nose (~2.84 cal).

The G7 is around 0.29 (my best guess), taking into account the EPR construction. So with a threshold MV of 915 m/s in the AR, the ballistics are very impressive.

smg762

From: smg762

21/9/21

Not to derail the topic, but has there been much development of coilguns/gauss guns.

-in terms of magnetically holding the bullet in place. And then getting some 'assistance' from the cartridge, removing the need for a big power source?

gatnerd

From: gatnerd

21/9/21

stancrist said:

Reliability of feeding, chambering, extraction with such an extreme L:D, and zero case taper?

Hard to say; 5.7x28 employs a similarly 'taperless' design, albeit shorter. Reliability is quite good, but coatings on the 5.7 brass may be a factor. 

A modification of the concept is certainly possible, where the case is made slightly wider in the rear and tapers forward. For example say something equivalent to .25 ACP at the base (0.278") tapering to 0.253" (neck diameter of current 5.56x45). 

Basically the design goals would be for a cartridge that allows:

- a 50rd double stack magazine that is ~ 8" long 

-Velocity and energy comparable to 5.56 / 5.45 

Anything after that would be open to the designers. 

gatnerd

From: gatnerd

21/9/21

VPMudde said:

The following is an estimate for the projectile made from images available online

Heres the only pic out there of the 6.8 GP, which may help with your estimates:

gatnerd

From: gatnerd

21/9/21

EmericD said:

But from Buffman video, the bullet seems highly magnetic, and tungsten carbide is not magnetic at all.

In the video, Buffman describes it as mildly magnetic. Various WC alloys are midly magnetic due to use of iron and cobalt in the alloy / binder:

https://blog.carbideprocessors.com/tungsten-carbide/tungsten-carbide-and-magnetism/

This lead me down an interesting rabbit hole of 'is M993 magnetic' which lead to this post:

https://www.migunowners.org/forum/showthread.php?399832-Thoughts-on-armor-piercing-bullets-in-AR-pistols/page2

So that cobalt binder could explain the magnetism, and also explains why both M993 and AP485 were pretty lame penetrators - they tended to shatter on impact. 

But the following paragraph is of extreme interest to the NGSW / AP problem, and could help explain why Buffman's testing is showing such very different results then what the US Army is expecting out of NGSW. It could also explain why your results with the MEN DM151 are so much better then M993. 

The use of a more shatter resistant tungsten formulation would radically change our expectations of what is possible for AP / NGSW. 

More info on Liquid Phase Sintered (LPS) Tungsten Alloy:

https://apps.dtic.mil/sti/citations/ADA474421

https://www.hindawi.com/journals/jpt/2014/764306/

https://www.hindawi.com/journals/jpt/2014/764306/

But overall this suggests there is a good bit of performance beyond what we've seen out of M993/AP485 out there by improvements in tungsten carbide production to make it more shatter resistant. 

And MEN may be using these better techniques then what NAMMO was doing with M993/AP485. 

This company in the US, which makes tungsten parts / fragments for the US military, makes mention of LPS in the production process:

https://tungstenparts.com/tungsten-manufacturing-operations/

Overall it may be the case that a newer, better tungsten AP has arrived and our previous understanding of NGSW's practicality - based on Buffman's testing - may no longer apply to the same extent. 

  • Edited 21 September 2021 17:41  by  gatnerd
VPMudde

From: VPMudde

21/9/21

EmericD said:

The bullet is longer (L/D ~5.15) with a slender nose (~2.84 cal).

A bullet like that is actually even lighter than my estimate, there being more nose cone and less shank. 

@Gatnerd: that is the exact image i got my estimate from. However, when I went to measure it again just now ended up at 5.1 caliber length, 2.67 cal nose cone, and 0.15 cal meplat. Still only gets you to 125.5 grains.

  • Edited 21 September 2021 20:59  by  VPMudde
stancrist

From: stancrist

21/9/21

Perhaps you are using incorrect density?

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