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

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

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

 

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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