Editing Shell (projectile) (section)

==Propulsion==
Artillery shells are differentiated by how the shell is loaded and propelled, and the type of breech mechanism.

===Fixed ammunition===
Fixed ammunition has three main components: the [[fuze]]d projectile, the [[Cartridge (firearms)|casing]] to hold the propellants and [[Detonator|primer]], and the single propellant charge. Everything is included in a ready-to-use package and in British ordnance terms is called [[Glossary of British ordnance terms#Fixed QF|fixed quick firing]].  Often guns which use fixed ammunition use [[Rifled breech loader#The sliding block|sliding-block]] or sliding-wedge breeches and the case provides [[obturation]] which seals the [[Breech-loading weapon|breech]] of the gun and prevents propellant gasses from escaping.  Sliding block breeches can be horizontal or vertical.  Advantages of fixed ammunition are simplicity, safety, moisture resistance and speed of loading.  Disadvantages are eventually a fixed round becomes too long or too heavy to load by a gun crew.  Another issue is the inability to vary propellant charges to achieve different velocities and ranges.  Lastly, there is the issue of resource usage since a fixed round uses a case, which can be an issue in a prolonged war if there are metal shortages.<ref name=":Hogg">{{Cite book|title=Artillery|last1=Hogg|first1=Ian |last2=Batchelor |first2=John H. |date=1972|publisher=Scribner |isbn=0684130920|location=New York|oclc=571972}}</ref>

===Separate loading cased charge===
[[File:3-112 live fires M777A2 and M119A3 howitzers 150826-Z-AL508-076.jpg|thumb|Semi-fixed ammunition for the [[M119 howitzer]], with the propellant cases and projectiles separated]]

Separate loading cased charge ammunition has three main components: the fuzed projectile, the casing to hold the propellants and primer, and the bagged propellant charges.  The components are usually separated into two or more parts.  In British ordnance terms, this type of ammunition is called [[Glossary of British ordnance terms#Separate QF|separate quick firing]].  Often guns which use separate loading cased charge ammunition use sliding-block or sliding-wedge breeches and during [[World War I]] and [[World War II]] Germany predominantly used fixed or separate loading cased charges and sliding block breeches even for their largest guns.  A variant of separate loading cased charge ammunition is '''semi-fixed''' ammunition.  With semi-fixed ammunition the round comes as a complete package but the projectile and its case can be separated.  The case holds a set number of bagged charges and the gun crew can add or subtract propellant to change range and velocity.  The round is then reassembled, loaded, and fired. Advantages include easier handling for larger caliber rounds, while range and velocity can easily be varied by increasing or decreasing the number of propellant charges.  Disadvantages include more complexity, slower loading, less safety, less moisture resistance, and the metal cases can still be a material resource issue.<ref name=":Hogg" />

===Separate loading bagged charge===
In separate loading bagged charge ammunition there are three main components: the fuzed projectile, the bagged charges and the primer.  Like separate loading cased charge ammunition, the number of propellant charges can be varied.  However, this style of ammunition does not use a cartridge case and it achieves obturation through a [[Interrupted screw|screw breech]] instead of a sliding block.  Sometimes when reading about artillery the term separate loading ammunition will be used without clarification of whether a cartridge case is used or not, in which case it refers to the type of breech used.  Heavy artillery pieces and [[naval artillery]] tend to use bagged charges and projectiles because the weight and size of the projectiles and propelling charges can be more than a gun crew can manage.  Advantages include easier handling for large rounds, decreased metal usage, while range and velocity can be varied by using more or fewer propellant charges.  Disadvantages include more complexity, slower loading, less safety and less moisture resistance.<ref name=":Hogg" />

===Range-enhancing technologies {{Anchor|RAP}}===
[[File:XM1113 in flight.jpg|thumb|upright=1.35|XM1113 extended-range artillery round, shown here at a range demonstration, uses a rocket-assist motor]]
Extended-range shells are sometimes used. Two primary types exist: [[rocket-assisted projectile]]s (RAP), which generate additional thrust via a rocket motor built into the base, and [[base bleed]] (BB), which reduce base drag by expelling gas into the low-pressure area behind the shell. These shell designs usually have reduced high-explosive filling to remain within the permitted mass for the projectile, and hence less lethality.