Boat Tail Shells

[Subdeacon Joe]

Found on FB:

 

Boat Tail vs Flat Base Battleship Shells

In the WW2 era, only the French and Japanese adopted the “Boat Tail” base shape for their Battleship shells.

The purpose of the boat tail on the shell base is that it allows the airflow to remain attached to the surface of the shell until it reaches the reduced diameter base, resulting in less base drag. 
Base drag is caused by the low-pressure ('suction') area created directly behind the shell as it travels through the air, slowing the shell.

Interwar testing by the Japanese revealed that just adding the boat tail to their 14” shells achieved a 2,000 yard range increase with no other shell or gun modifications.

Ballistician Bryan Litz wrote that the boat tail allows the projectile to "retain velocity / energy at long range, as well as less drop and wind deflection".

The 38cm / 15” APC shells manufactured by the US firm of Crucible Steel for Richelieu in 1943 retained the boat tail base, although not exactly identical to the original French shell profile…

The Royal Navy discovered in 1945 that putting a tracer on large calibre shells reduced the base drag effect, but information is lacking on how much research was done and the extent these tracers were implemented on existing shells.
Post WW2 the RN did have a 14" APC projectile designated "Shell, Breach-Loading, Armour-Piercing with Cap, 14-Inch, Heavy, K, Mark IB Night Tracer" that presumably had a tracer base plug fitted.

As a follow-up, in the 1960’s the projectile base bleed or base burn system was developed in Sweden to increase artillery range by expelling burning gas (similar to a tracer) into the low pressure area behind the shell to reduce base drag, this extended the range of the modified shells by around 20–35%. 

The boat tail projectile shape should be very familiar to you rifle shooters….

Many thanks to Ed Low for his assistance 
Diagram made by (FB Author)."

 

[Pat Riot]

Hmmm…We called them “projectiles”. Is “shells” a valid WW2 term?

[watab kid]

im inclined to projectile in this case as well as most battleship guns were loaded with that then the BP charges to send it where it was going , 

[Subdeacon Joe]

It seems that either is acceptable.  And, I think that technically, since the projectiles are hollow and filled with explosives, they are "shells." Just as with muzzle loading artillery which had solid shot, "common shell," spherical case, and canister. 
https://en.wikipedia.org/wiki/16-inch/50-caliber_Mark_7_gun

The Mark 7 gun was originally intended to fire the 2,240-pound (1,020 kg) Mark 5 armor-piercing shell. However, the shell-handling system for these guns was redesigned to use the "super-heavy" 2,700-pound (1,200 kg) APCBC (Armor Piercing, Capped, Ballistic Capped) Mark 8 shell before any of the Iowa-class battleship's keels were laid down. The large-caliber guns were designed to fire either an armor-piercing round for anti-ship and anti-structure work, and a high-explosive round for use against unarmored targets and shore bombardment.

The North Carolina and South Dakota classes could also fire the 2,700-pound Mark 8 shell with the 16"/45 caliber Mark 6 gun, although with a shorter range. The Mark 6 gun was not as heavy as the Mark 7, which helped both battleship classes to conform to the limits of the Washington Naval Treaty. However, the two treaty-era battleships fired their shells at a lower muzzle velocity, which made their plunging fire superior to that of the 16"/50 caliber gun.^[6]

The Mark 8 shells gave the North Carolina, South Dakota, and Iowa classes the second-heaviest broadside of all battleship classes, even though the two ships were treaty battleships, exceeded only by the Yamato-class super-battleships.

Each D839 propellant (smokeless powder) grain used for full charges for this gun was 2 in (51 mm) long, 1 in (25 mm) in diameter and had seven perforations, each 0.060 in (1.5 mm) in diameter with a web thickness range of 0.193 to 0.197 in (4.9 to 5.0 mm) between the perforations and the grain diameter. A maximum charge consisted of six silk bags (hence the term "bag gun"), each filled with 110 lb (50 kg) of propellant.^[1]

and

http://www.navweaps.com/Weapons/WNUS_16-50_mk2.php
^Shell stowage for the South Dakota class was to be as follows:

• Each of the four mountings had 212 projectiles distributed as follows:
  •   62 projectiles in the shell handling room
  • 138 projectiles in the turret stool
  •   12 projectiles in the shell hoists
• Turret #2 had 48 projectiles on the third deck.
• There were an additional 541 projectiles stowed in shell rooms on the first platform deck.

In total, the planned stowage was 1,437 projectiles.

[Pat Riot]

Perhaps when I joined the Navy they had rid themselves of the term “shell”. I do recall a gunnery instructor giving us a stern lecture on terminology. The words “bullet, shell, slug” and a couple of others regarding what the “guns” fired were forbidden under penalty of a stern talking to and shaming. 
(Guns is in quotations because guns are mounted to the ship. Small arms were not “guns”)

[Stump Water]

I use boat-tail bullets almost exclusively for the cartridges I reload with a bottle-neck case.

 

These are the go-to for .243 Win.

 

These are also a favorite. 

[Still hand Bill]

G1 shape vs G7 shape, it’s been driven by long range shooting sports and long range hunting.  It’s been interesting to listen to the Hornady podcast and then start looking at bullet stability, length, weight per caliber, twist rate.  Older SAAMI spec cartridges are mostly designed around G1 shapes and thus slower twist and lower BC.  Newer cartridges are G7 shapes, longer, heavier for caliber and need faster twists.  Since action lengths are fixed it has required new cartridges to be developed to get the longer bullets to fit correctly in a magazine.   Imho interesting and can see the development over time.

[Big Sage, SASS #49891 Life]

I too use Boattail bullets in all my hunting and target loads. I load them for .300 Wby Mag. 30-06 25-06 and .220 Ackley Improved Swift. Bettet accuracy and velocity. This is my .220 , notice the chrono velocity. I also did the stockwork on it.

[The Original Lumpy Gritz]

Match grade rifle bullets use that profile.

Far more stable at long distance than flat base. 

Especially in the wind.

 

[Subdeacon Joe]

4 hours ago, Pat Riot said:

Perhaps when I joined the Navy they had rid themselves of the term “shell”. I do recall a gunnery instructor giving us a stern lecture on terminology. The words “bullet, shell, slug” and a couple of others regarding what the “guns” fired were forbidden under penalty of a stern talking to and shaming. 
(Guns is in quotations because guns are mounted to the ship. Small arms were not “guns”)

 

Projectile covers everything that can be loaded....all shells are projectiles, not all projectiles are shells.  

Your last point is why I can honestly say that I have no guns in the house.  No guns, no howitzers, no mortars.

[Pat Riot]

4 hours ago, Subdeacon Joe said:

 

Projectile covers everything that can be loaded....all shells are projectiles, not all projectiles are shells.  

Your last point is why I can honestly say that I have no guns in the house.  No guns, no howitzers, no mortars.

And no ammunition. Self propelled projectiles, maybe.