Odd range trade-offs based on shell weight.

[Woodrow]

New to this game, very much enjoy it so far, but I've found an oddity that defies physics.  When selecting shell weight, the trade off from selecting a heavier shell is reduced muzzle velocity but an increase in range.  From a physics perspective (and anyone the reloads and shoots firearms regularly could tell you) weight of the projectile itself does not increase or decrease range.  All things being equal, only two factors affect projectiles range: 1) Muzzle Velocity & 2) Ballistic Coefficient (how much drag a projectile has).  Again, with small arms and large rifles, your limitations on muzzle velocity are based on the maximum pressures the rifles can withstand.  So, if you are firing a heavy shell and a light shell out of the same barrel with the maximum powder charge its rated for, the lighter shell would indeed have a higher muzzle velocity, but it is extremely unlikely that the larger shell would have such an improved ballistic coefficient to overcome that reduction in velocity to out-range it (and why would a naval artillery shells have such drastically different BCs).  To further buoy the point, the below link from the USS North Carolina museum warship site shows the fact:

http://www.battleshipnc.com/16-inch-main-battery-big-guns/

Note the lighter HE rounds out-range the heavier Mark 8 AP shells by about 2 miles.

[arkhangelsk]

There is already a similar thread here for the topic:

 

[akd]

Yes, this needs additional work, but it’s not quite so simple:

Range with the originally planned 2,240 lbs. (1,016 kg) AP Mark 5 was 40,200 yards (36,760 m) at a muzzle velocity of 2,520 fps (768 mps).

http://www.navweaps.com/Weapons/WNUS_16-45_mk6.php

So still heavier shell than HC and lower MV, but ever so slightly longer range.

And for same two shells described at the North Carolina site (2700lb AP, 1900lb HC) fired from the later 16”/50 Mark 7, the slower, heavier AP has greater range at 20 degrees elevation and higher.

Range

 

Ranges of projectiles fired at new gun muzzle velocities

Elevation	AP Mark 8	HC Mark 13
10 degrees	17,650 yards (16,139 m)	18,200 yards (16,642 m)
15 degrees	23,900 yards (21,854 m)	24,100 yards (22,037 m)
20 degrees	29,000 yards (26,518 m)	28,800 yards (26,335 m)
25 degrees	33,300 yards (30,450 m)	32,700 yards (29,901 m)
30 degrees	36,700 yards (33,558 m)	36,000 yards (32,918 m)
35 degrees	39,500 yards (36,119 m)	38,650 yards (35,342 m)
40 degrees	41,430 yards (37,884 m)	40,600 yards (37,163 m)
45 degrees	42,345 yards (38,720 m)	41,622 yards (38,059 m)

http://www.navweaps.com/Weapons/WNUS_16-50_mk7.php

Edited January 28, 2020 by akd

[SmoCro]

@Woodrow:

What about inertia?

At least in firearms ballistics the weight of the projectile is a factor as heavier projectiles are more stable and retain energy better than smaller ones which are less stable.