Hellsing ARMS Casull

The Hellsing ARMS .454 Casull Auto (usually referred to as simply "Casull") is a very powerful handgun and one of the first personal firearms wielded by Alucard.

The engraving on the frame of the gun (Hellsing ARMS 000001) indicates that it is the first custom weapon ever made by Walter C. Dornez.

Profile
The Casull is a semi-automatic magnum pistol, based on two pre-WW1 handgun designs by Colt: the M1903 and M1905 pistols (the early versions of the M1911). The gun weighs approximately 6 kg unloaded and has a magazine capacity of six .454 Casull cartridges.

The overall design of the Casull is simple, using the Browning short recoil mechanism. Its most recognizable feature is its long slide, counteracting the weapon's heavy recoil with its weight. The barrel is 10 inches long (specified on the slide) and finished with titanium nitride which gives it a characteristic gold color.

The Casull is able to kill normal vampires with only 1 shot. It is too heavy and unwieldy for a human to use, yet a perfect match for Alucard's strength.

Ammunition and Usage
The gun fires custom-made explosive .454 Casull rounds, with the steel bullets bearing a core made from the melted silver Christian cross from Manchester Cathedral. They are used in a six round single-stack magazine.

Although Alucard has reloaded it at many points throughout both the manga and anime, Hirano has joked in the back of volume 1 that "They're all cosmoguns that can hold a million rounds". This is also evidenced in the first OVA, where Alucard takes out a large group of ghouls without reloading.

Early on, Alucard used the Casull alone to terminate all sorts of vampires, including the fake vampire priest in Cheddar. After acquiring another weapon, he still uses the Casull along with this new weapon.

Failure to stop Anderson & the Jackal
However, in both the anime and the manga, the Casull fails to kill Alexander Anderson, so Alucard specifically asks Walter for "something bigger" (however, he may have been refering to the ammunition). This led to the creation of the Jackal, a 13mm handgun that has the same size as the Hellsing Arms Casull, but fires even more powerful rounds. Alucard often dual wields these two pistols later on.

Contradictions with the ammunition
Alucard's first gun is chambered in .454 Casull (11.23mm), however he claims that it fires 13mm rounds. A possible explanation would be that the gun was originally chambered in .454 Casull, but now fires a custom round necked up to 13mm, as the casings shown ejected by the pistol are bottle-necked and rimless, while the real Casull round uses a straight walled rimmed case. Therefore it can be assumed that the .454 Casull Pistol uses the same bullet from the .454 Casull cartridge, but the casing is a custom design made by Hellsing Arms.

Another explanation: if one would add the numbers 4 5 4, the sum will be 13, hence the 13mm rounds. And therefore an error on the author's knowledge about ammunition.

Even though Alucard has stated that the Casull uses explosive ammo, the traits exhibited by the bullet wounds show that it displays characteristics similar to that of a full metal jacketed pistol round, when it punches through the lung of two people without having the round explode.

Trivia

 * .454 Casull is a big-game revolver cartridge, basically a magnumized version of the .45 Colt round. The .454 is twice as powerful as the .44 Magnum, and even more powerful than the .50AE of the Desert Eagle.
 * When used together with the Jackal, the Casull gives Alucard an appearance similar to Dante, the protagonist of the Devil May Cry series. Both are red-clad transhumans (a vampire and a half-demon, respectively) who wield a white and a black gun simultaneously (Casull and Jackal for Alucard, Ebony and Ivory for Dante).
 * However the two pairs of guns vary vastly in stopping power as Dante's pistols are chambered in much weaker .45 ACP and instead are powered by Demon energy to shoot rapid barrages w/ infinite ammo.
 * Alucard has been seen with the ARMS Casull in WWII flashbacks which is anachronistic since the .454 Casull round was not developed until 1957.
 * It made its final appearance in OVA 9, it's nowhere to be seen after it was last shot to Luke Valentine. Although, it was seen when Alucard aimed it along with the Jackal at Alexander Anderson in OVA III and OVA IV.