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NGSW Reset / Change in Direction   General Military Discussion

Started 16-Nov by Guardsman26; 13304 views.
EmericD

From: EmericD

22-Nov

Guardsman26 said:

The question is what muzzle energy and mass does a low drag 6.5 mm EPR bullet need to penetrate Level IV body armour at 400 metres Maybe Emeric knows and can suggest what case capacity is needed.

Well, let's start with the hypothesis that a 16 mm RHA plate is a ballistic equivalent of "most" Level IV body armour.

With a "PPI" or RUAG HC bullet structure and a bullet with a L/D of 5, we will have enough room for a 29 mm long steel penetrator (6 mm bullet), or 31.5 mm (6.5 mm bullet).

We will then need an impact velocity of ~790 m/s for the 6 mm bullet, or ~750 m/s for the 6.5 mm bullet in order to defeat the 16 mm plate 50% of the time.

You could expect to defeat this plate up to 200 m with a 6 mm, and 250 m with a 6.5 mm (MV around 915 m/s and C7 around 0.25).

Now, if the penetrator is WC (with the same length), we will need only an impact velocity of ~620 m/s (6 mm bullet) or ~560 m/s (6.5 mm bullet) to defeat the same 16 mm RHA plate, or around 500 m (6 mm) or 600 m (6.5 mm) with the same exterior ballistics hypothesis.

stancrist

From: stancrist

22-Nov

EmericD said:

6.8 mm CT is 12 mm in diameter, and ~2.5" long

Is that confirmed?  I thought I remembered you posting sometime back that it is 0.480" diameter.

It certainly looks slightly fatter in the photo, and measuring it on the screen, there is a difference.

  • Edited 22 November 2021 5:25  by  stancrist
stancrist

From: stancrist

22-Nov

You gave two different definitions of "effective volume":

   1.  the size of a 20 or 30 round magazine.

   2.  a cylinder of the maximum cartridge diameter with a length that extends to the tip of the bullet.

In regard to the three NGSW candidate cartridges, I would opine that their dimensional differences are so small as to have no practical consequence.

In other words, even though the CT round is a little bit shorter, there won't be room on the soldier's vest for more Textron mags than SIG or TV mags.

poliorcetes

From: poliorcetes

22-Nov

Thanks a lot. 

My problem is that I just cannot figure out how the chamber can misalign with bore entry. I mean, the height of the chamber is guided by the “s” rail and it can and should be designed and built with the minimum tolerances possible. Say, 20 years ago it should be evolved like so in order to reach TRL 3 at best.

How could a tilting chamber had a misalignment which could produce the mentioned effect?

Gr1ff1th

From: Gr1ff1th

22-Nov

An important consideration wrt to CT magazines is the forced single feed design, this will always add additional height, or reduce capacity, to CT magazines versus conventional, in addition to the increased base diameter of CT cartridges, the Textron 20 round magazines are noticeably larger than either the SIG or TV/LSFW magazines both in height and thickness, It doesn't suffer from this in the belt fed format obviously, Overall it's not really a deal-breaker, just something to consider.

Regarding belt feds, I'd kill to see a lightweight belt-fed "6mm CT optimum" carbine, similar to what Kori originally envisioned for the CT carbine before the program was taken away from her.

 

  • Edited 22 November 2021 9:49  by  Gr1ff1th
EmericD

From: EmericD

22-Nov

stancrist said:

It certainly looks slightly fatter in the photo, and measuring it on the screen, there is a difference.

Well, using this picture and GIMP to measure things, I obtain 227 pixels for the x51mm case length and 53 pixels for the case width, so 53 / 227 x 2.015" = 0.470" for the 7.62 mm casehead which seems OK.

The 6.8 mm CT round seems to be 291 px long by 56 px in diameter, so 56 / 227 x 2.015 = 0.497".

So contrary to what I said the case is probably closer to 0.50" than 0.473", with a length of 2.58" (let's say 2.6").

stancrist

From: stancrist

22-Nov

Gr1ff1th said:

An important consideration wrt to CT magazines is the forced single feed design, this will always add additional height, or reduce capacity, to CT magazines versus conventional...

Right.  When doing my analysis, I forgot about the increase in magazine height caused by the single-feed design. 

stancrist

From: stancrist

22-Nov

EmericD said:

The 6.8 mm CT round seems to be 291 px long by 56 px in diameter, so 56 / 227 x 2.015 = 0.497". So contrary to what I said the case is probably closer to 0.50" than 0.473", with a length of 2.58" (let's say 2.6")

Thanks, Emeric.  Your measurements are much more precise than what I was able to do. 

I figured 2.6" for the height, but was unsure how much bigger than 0.47" the diameter is

Anyway, it seems the cartridge volumes are essentially the same for all three candidates.

  • Edited 22 November 2021 21:15  by  stancrist
nincomp

From: nincomp

22-Nov

stancrist said:

In regard to the three NGSW candidate cartridges, I would opine that their dimensional differences are so small as to have no practical consequence.

My main point is that claims of volume reduction must be taken with a grain of salt.  Even though a particular company may claim that one cartridge has reduced volume when compared to another, that may or may not result in an individual soldier being able to carry more of it in loaded magazines.   

The comment about "effective volume" was primarily to point out that the true geometric volume of a cartridge is not always the best metric to use.  Below is a photo of 6mm Creedmoor, 260 Rem, and 308 cartridges.  The geometric volume of each is different, but they all use the same size magazine.  They are effectively the same volume when loaded in magazines.

stancrist

From: stancrist

23-Nov

nincomp said:

The comment about "effective volume" was primarily to point out that the true geometric volume of a cartridge is not always the best metric to use. 

Until you mentioned it, I haven't seen anyone talk about geometric volume.  As I understood the comments made by others, everyone seems to have been referring to what you call "effective volume" when discussing the volume of a cartridge.

nincomp said:

6mm Creedmoor, 260 Rem, and 308 cartridges.  The geometric volume of each is different, but they all use the same size magazine.  They are effectively the same volume when loaded in magazines.

And the situation is somewhat different with 6.8 CT versus 6.8 SIG and 6.8 TV.  Even though the CT round is fatter and shorter than the SIG and Tv cartridges, it has the same volume.  However, when loaded in magazines, 20 rounds of CT ammo occupy more volume due to how the cartridges stack near the top of the single-feed magazine (similar to the photo below).

The resulting increase in magazine height compared to the SIG and TV double-feed magazines is not enough to affect how many magazines a soldier can carry, but the fatter cartridges may adversely impact logistics by decreasing the number of rounds that can be packed and shipped in containers.

  • Edited 23 November 2021 5:06  by  stancrist
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