H_Minus said...

stancrist said...

 M1 rifle, 24" bbl; M1919 machine gun, 24" bbl

  M14 rifle, 22" bbl; M60 machine gun, 22" bbl

  M16 rifle, 20" bbl; M249 machine gun, 18" barrel

  M4 carbine, 14.5" bbl; M249 machine gun, 14.5" bbl

Others you left out:

M16 rifle, 20" bbl; M60 machine gun, 22" bbl

M4 carbine, 14.5" bbl; M240 machine gun, 24.5" bbl

Omitted because they're apples vs watermelons nonsense.  Need to compare weapons in the same caliber.  Otherwise, you could take such silliness to extreme, and compare 5.56mm M4 to .50 M2.

 

H_Minus said...

M4 carbine, 14.5" bbl; M249 machine gun, 18" bbl

I doubt those units which are "pure fleeted" with M4 carbines use 18" barrel M249s.  You're just arguing for the sake of arguing.

stancrist said...

 

NathanielF said...

...the light 85gr bullet satisfies the Army's requirement for a round that can be used in training ranges. The Army has shown that they will accept combat rounds with lead cores (e.g., Mk. 262 being used outside of SOCOM) as long as those rounds are not being used for training. Great, so here's where you cheat. If more range is desired, additional loads can be introduced or brought out from stores that have heavy, lead-cored bullets in either OTM (for DMRs) or steel-jacketed FMJ (for SAWs/MGs) bullets to meet those additional requirements...

The problem with the above idea is that the Army has shown they want only one round for both training and combat.

 

NathanielF said...

This does mean there would need to be additional suites of tracers, etc...

Same problem as above.  The Army wants only one standard tracer, etc, round.

 

Yes, as mentioned in the OP, I am cheating known requirements a bit. The proposal shouldn't be taken too seriously, therefore.

Several messages on this thread have been deleted - see post No.28 to see why.

 

Some random notes of mine. The three tests below pointed me towards an ogive length of 2.6-2.9 as being ideal when optimizing for velocity retention. The zip file at the bottom was a GPC caliber configuration study, optimizing for lowest weight:

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Bullet Weight Ballistic Test:

Keeping the cartridge case, overall length, caliber, bullet shape, and pressure constant, bullet weight was varied in 5 grain increments to determine the ideal weight for caliber.

Barrel length was kept constant at 14.5"

Distance of virtual chronograph was kept constant at 0.

The constants were:

OAL: 57.4mm

Base diameter: 9.6 mm

Case Length: 42.000mm (1.654")

Neck length: 0.884 caliber

Case capacity: 28.05 grs H2O

Pressure: 49500 CUP

Bullet base: 9 degree boattail, 0.749 cal diameter, 0.795 cal length

Bullet shank: 0.759 cal

Meplat: 0.15 cal

Free space: 2.707 caliber

Bullet ogive length: 2.608 caliber

Bullet ogive radius: 8.480 caliber

Bullet overall length: 4.260 caliber

i7 FF: 0.972

Caliber: 0.224"/5.69mm (5.56mm nominal)

Bullet overall length: 4.260 caliber (0.954")

 

40 gr (2.59 g)

G7 BC (averaged from Mach 1.2-3.0): 0.117

Muzzle velocity: 3,482 ft/s

200m velocity: 2,573 ft/s

Max range of 1,800 ft/s velocity: 401 m

200m energy: 797.2 J

500m energy: 261.1 J

1,000m energy: 78.8 J

 

45 gr (2.92 g)

G7 BC (averaged from Mach 1.2-3.0): 0.132

Muzzle velocity: 3,310 ft/s

200m velocity: 2,517 ft/s

Max range of 1,800 ft/s velocity: 412 m

200m energy: 858.2 J

500m energy: 321.0 J

1,000m energy: 98.9 J

 

50 gr (3.24 g)

G7 BC (averaged from Mach 1.2-3.0): 0.146

Muzzle velocity: 3,162 ft/s

200m velocity: 2,457 ft/s

Max range of 1,800 ft/s velocity: 416 m

200m energy: 908.4 J

500m energy: 373.4 J

1,000m energy: 118.6 J

 

55 gr (3.56 g)

G7 BC (averaged from Mach 1.2-3.0): 0.161

Muzzle velocity: 3,032 ft/s

200m velocity: 2,402 ft/s

Max range of 1,800 ft/s velocity: 421 m

200m energy: 

500m energy: 426.6 J

1,000m energy: 139.6 J

 

60 gr (3.89 g)

G7 BC (averaged from Mach 1.2-3.0): 0.176

Muzzle velocity: 2,917 ft/s

200m velocity: 2,350 ft/s

Max range of 1,800 ft/s velocity: 422 m

200m energy: 997.7 J

500m energy: 476.3 J

1,000m energy: 160.8 J

 

65 gr (4.21 g)

G7 BC (averaged from Mach 1.2-3.0): 0.190

Muzzle velocity: 2,814 ft/s 

200m velocity: 2,297 ft/s

Max range of 1,800 ft/s velocity: 418 m

200m energy: 1,032.6 J

500m energy: 518.9 J

1,000m energy: 181.3 J

 

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Bullet Caliber Ballistic Test:

Keeping cartridge overall length, base diameter, pressure, bullet weight, density* and shape constant, I steadily incremented the caliber, with corresponding changes in case capacity.

Barrel length was kept constant at 14.5"

Distance of virtual chronograph was kept constant at 0.

*As density only affects the stability of the bullet and not its ballistic coefficient, it does not need to be estimated for the purposes of this analysis and has therefore been arbitrarily kept constant.

 

The constants were:

OAL: 57.4mm

Base diameter: 9.6 mm

Neck length: 0.884 caliber

Pressure: 49500 CUP

Bullet weight: 55 gr

Bullet density: 10.5 g/cm^3

Bullet base: 9 degree boattail, 0.749 cal diameter, 0.795 cal length

Bullet shank: 0.759 cal

Meplat: 0.15 cal

Free space: 2.707 caliber

Bullet ogive length: 2.608 caliber

Bullet ogive radius: 8.480 caliber

Bullet overall length: 4.260 caliber

i7 FF: 0.972

 

Caliber: 0.183"/4.65mm (4.5mm nominal)

Bullet overall length: 4.260 caliber (0.779")

G7 BC (averaged from Mach 1.2-3.0): 0.241

Case Length: 44.819mm (1.765")

Case capacity: 29.68 grs H2O

Muzzle velocity: 2,886 ft/s

200m velocity: 2,468 ft/s

Max range of 1,800 ft/s velocity: 563 m

500m energy: 603.4 J

1,000m energy: 213.6 J

 

Caliber: 0.204"/5.18mm (5mm nominal)

Bullet overall length: 4.260 caliber (0.869")

G7 BC (averaged from Mach 1.2-3.0): 0.194

Case Length: 43.375mm (1.708")

Case capacity: 28.82 grs H2O

Muzzle velocity: 2,979 ft/s

200m velocity: 2,456 ft/s

Max range of 1,800 ft/s velocity: 488 m

500m energy: 521.6 J

1,000m energy: 166.1 J

 

Caliber: 0.224"/5.69mm (5.56mm nominal)

Bullet overall length: 4.260 caliber (0.954")

G7 BC (averaged from Mach 1.2-3.0): 0.161

Case Length: 42.000mm (1.654")

Case capacity: 28.05 grs H2O

Muzzle velocity: 3,032 ft/s

200m velocity: 2,402 ft/s

Max range of 1,800 ft/s velocity: 421 m

500m energy: 426.6 J

1,000m energy: 139.6 J

 

Caliber: 0.243"/6.17mm (6mm nominal)

Bullet overall length: 4.260 caliber (1.034")

G7 BC (averaged from Mach 1.2-3.0): 0.137

Case Length: 40.694mm (1.602")

Case capacity: 27.37 grs H2O

Muzzle velocity: 3,055 ft/s

200m velocity: 2,320 ft/s

Max range of 1,800 ft/s velocity: 364 m

500m energy: 332.1 J

1,000m energy: 117.2 J

 

Caliber: 0.264"/6.71mm (6.5mm nominal)

Bullet overall length: 4.260 caliber (1.124")

G7 BC (averaged from Mach 1.2-3.0): 0.116

Case Length: 39.250mm (1.545")

Case capacity: 26.67 grs H2O

Muzzle velocity: 3,052 ft/s

200m velocity: 2,197 ft/s

Max range of 1,800 ft/s velocity: 307 m

500m energy: 232.1 J

1,000m energy: 94.3 J

 

------

 

Bullet Ogive Ballistic Test:

Keeping cartridge overall length, base diameter, pressure, bullet weight and density*,  base, and shank, meplat, and caliber constant, I steadily increased the ogive length, and correspondingly decreased the case length in increments of 2mm.

All ogives were of the tangent type.

Barrel length was kept constant at 14.5"

Distance of virtual chronograph was kept constant at 0.

*As density only affects the stabili

Another study I did to attempt to create a formula that would show the relationship between BC and muzzle velocity while holding drop constant at 500m (equal to an M4 firing M855). The formula I came up with is below:

MV = 2950 / ([BC / 0.150]^[1/5.215])

BC = 0.150 * ([2950 / MV]^5.215)

It's pretty accurate from about 2,300 ft/s and up or .5 G7 BC and below, but outside of those parameters it doesn't work so well.

Velocity is clearly a very important component to terminal effectiveness and suppression, all by itself. If we accept the idea that by optimizing for velocity retention, we can get the best effectiveness for weight, we find that there are in fact options that allow us to reduce weight vs. a Williams-style 6.5mm GPC, while even increasing velocity retention. The example below makes similar assumptions to previous GPC models I've created, such as very good form factor (.889, the same as the Balle D), and pressure (50,000 CUP via Powley). 

One possible incarnation of this is the .23 caliber round shown below:


 

Dimensions are 6(5.8 nominal)x44x10.8x62.2, firing a 5g bullet with a modified (improved) Balle D contour and EPR-type construction. None of that's the point, though; see the graphs below. The first is for M855 from an M4:

Next M80 from a 22" barrel:

Note that both have fairly poor velocity retention. At 600m, 5.56 has entered the transonic regime and has no more velocity than standard pressure 9mm does at the muzzle, with a bullet half the weight. It would still poke a deep hole, but we can expect nothing exotic in the way of terminal effect. 7.62mm is doing a little better; it's above transonic speeds, though only barely and has much better energy. There's no guarantee that 7.62 NATO would do anything more exotic than poke a hole either, but it certainly has greater potential to be effective at that range.

Alright, so the 7g/854m/s GPC we all know and love, equipped with an excellent .889 FF bullet:

No question that at 600m these figures are better than 7.62 NATO. Velocity is significantly higher and energy is almost equivalent. The 6.5mm stays above the transonic for almost another 200 yards, and the additional striking velocity means it's more likely that the 6.5mm will retain remote wounding characteristics at these ranges. So far so good. Now, moving forward, if we make the case that striking velocity is the more important factor in terminal effectiveness than raw energy due to the possibility of effects such as fragmentation and remote wounding, and if we are designing a caliber that must be as effective as possible at 600m at the lowest round overall weight, then we can potentially improve on the 6.5mm GPC in terms of weight. A round like this should be designed with careful consideration of the projectile shape (making it as fine as possible - though note both the 6.5mm and 5.8mm in this example use the same .889 FF bullet shape), projectile weight (as light as possible while retaining adequate SD), and muzzle velocity (as high as possible). Some of the groundwork for how to accomplish this is outlined in the notes above. A result (not the only one) is the 5.8mm round shown above. Its ballistics are as follows:

At 600m, it has nearly 100 ft/s higher velocity than the 6.5mm GPC, and energy not too far off, either. This means that the theoretical potential terminal performance is very high at 600m - one could indeed make a serious case that either round is more lethal than 7.62mm NATO at 600m. The bullet weight being reduced by 2g and muzzle energy being reduced by almost 350 J mean the round should be much lighter. Note that both projectiles had the same form factor (in fact, both are homologues I have modeled in SW) - therefore the performance of each round is 'tied' to the other. If only a .92 FF is feasible, for example, then either round will lose performance accordingly. Also note the high retained energy at a kilometer - not as high as either the GPC or 7.62 NATO, but more than double that of 5.56mm. Specific energy at a kilometer is decidedly superior to 7.62 NATO, and not far off of the 6.5mm.
 
Calculating round weight, we get 15.1 grams cartridge weight with a brass case, or 14.6 grams with a steel case. 26% weight increase vs. 5.56mm beats a 58% weight increase such as that incurred by the 7g loading of the .264 USA.

I think this demonstrates that even if one of the premises of the GPC concept is accepted - that the IW needs more range and effectiveness than 5.56mm can provide - that there is quite a lot of design space that could potentially provide effectiveness approaching or even above what's possible with a 6.5mm GPC at a lower weight increase.

I'm hoping Emeric will have finished "polishing" his revised article soon, since he makes some fascinating points about hit probability and suppression.

Very briefly, he points out that >99% of shots fired in combat miss (at any range); and that for every shot which hits, another 10 pass within a metre of the target and are therefore likely to have a suppressive effect. So small arms are principally about suppression. And the better the external ballistics, the higher the percentage of bullets fired will arrive in the suppression zone.

Furthermore, not all bullets suppress equally. After examining experimental results, he comes up with a proposal for a formula to calculate the differences depending on two factors: the noise made in passing (a function of shape, size and velocity) and the physical impact of near misses (linked to bullet momentum - velocity x mass). The product of those two gives you a score, which varies with range - e.g. the 7.62x39 AK suppresses almost as well as 7.62x51 at short range, but loses out as the range lengthens. The upshot is that small calibres tend to be poor at suppression. Testing of a flechette round revealed that it hardly had any suppressive effect at all.

However, I mustn't steal all of Emeric's thunder - he is bringing some very welcome fresh thinking to this field.

 

It seems rather doubtful that either your 5.8mm round or the 6.5mm GPC would fragment at 600 meters.