Tuesday, July 6, 2010

Actions: Bolt Action

In the last couple of posts, we studied the break-open action and the sliding barrel action. Now we will study another type of action that is known for its sturdiness and is still with us. This action is the bolt action.

We actually studied the first weapon to use a bolt action a while earlier. It happens to be the Dreyse Needle Gun. This gun had a number of firsts to its name:
  1. It was the first mass-produced military weapon using breech-loading technology.
  2. The ammunition it used burned almost completely, so it didn't need to eject the paper casing after firing the weapon. This was a precursor to caseless ammunition.
  3. It was the first bolt-action breechloading weapon.
The action was a significantly new invention in 1841, when the Dreyse needle gun was first introduced. It allowed the user to reload significantly faster than the opposition who were still using muzzle-loading weapons (almost 5 times the shooting speed). It also had the advantage that the user didn't need to stand up to reload the weapon and therefore could hide behind cover.

The basic idea of a bolt-action weapon is a manually operated bolt, which is manipulated by a handle, typically on the right side of the weapon. The handle is used to unlock the bolt and open the breech cover. The old cartridge case is then ejected from the breech chamber. The opening of the bolt may also cock the weapon in some models. Then a new cartridge is put in the chamber and the handle is then moved forward to close the bolt. In some models, the action of closing the bolt cocks the weapon. The weapon is then ready to fire.

In some models, opening the bolt causes an extractor lever to automatically pull the old cartridge case out of the chamber to eject it. The magazine has a spring that pushes a new cartridge into the chamber, when the old cartridge case is pulled out by the extraction lever. Such a mechanism is used in many bolt-action rifles, such as the Springfield M1903 rifle which carries a 5-shot magazine under it. This speeds up shooting because the user doesn't need to waste time pulling out the old cartridge or feeding a new one by hand.

Compared to other actions, the bolt-action has a few advantages. It is extremely simple to make, yet has very high accuracy. It is very cheap to manufacture and very light-weight. Best of all, it is a very strong action and can handle powerful cartridges. The only downside to it is that it doesn't support a very high rate of fire compared to some other alternatives. Since most modern military rifles are semi-automatic or selective fire weapons, they don't use this mechanism. However, the simplicity combined with the accuracy and the ability to handle high powered cartridges make it ideal to be used in sniper rifles. In fact, the bolt-action is overwhelmingly the action of choice in most of the sniper rifles used throughout the world. This mechanism is also used in many hunting rifles, where rate of fire is not as important as accuracy and power.

There are three major variants of bolt-action rifles which we will study below.

The Mauser M-98 system was first introduced in 1898 (hence M-98) with the Mauser Gewehr 98 rifle, which was used by the Germans between 1898 and 1935. This highly successful bolt-action design was later used in a lot of other rifles and is the dominant form of bolt-actions used today. In this type, the rifle is cocked when the bolt-action is opened. The Gewehr 98 has a 5-round magazine.

Click image to enlarge

The image above shows an original Mauser model from 1898. The weapon was designed with a lot of thought. The bolt handle is securely attached to the bolt and there are a couple of gas vent holes built into the bolt, so that if there is a rupture in the cartridge case or primer, the hot gases will vent out of the magazine hole instead of near the user's face. The "controlled feed" extractor claw holds on to the cartridge the moment it has fed from the magazine and holds on to it until the cartridge case is ejected. The weapon is cocked as the bolt is opened (actually, it specifically cocks as the bolt handle is rotated upwards, before pulling back to open the bolt) and the rear part of the striker protrudes from the back of the bolt, which allows one to quickly check if the rifle is cocked or not visually. The original mauser design was not given to cheap mass-production.

The cock-on-bolt-opening design was later adopted by other rifles as well, notably the Springfield M1903 (like the one shown in the picture above). The M1903 was used in the US military from 1903 all the way into the Vietnam war. The cock-on-bolt-opening design rifles are slightly slower to load than the other variant which we will study below. However, it is the more common of the two variants of bolt action and is used in nearly all modern hunting rifles today. It was also the dominant form of action used between the 1890s and the mid 1900s.

Another variant of bolt action is the cock-on-bolt-closing design. This is famously called the "Lee Enfield design" as it was first used in the Lee-Enfield rifle of 1895, otherwise known as the SMLE (Short Magazine Lee-Enfield) rifle. This rifle was heavily used in the British Commonwealth and its descendant is still used by Indian police, which makes it the longest serving bolt-action rifle model in existence.

The above is an example of a Lee-Enfield Mark I rifle. In this rifle, pushing the bolt closed cocks the rifle. This makes opening the bolt a lot faster and smoother, compared to the cock-on-opening design of the Mauser. This feature, coupled with its larger capacity 10-round magazine meant that a user could shoot 20-30 times in 60 seconds, making it the fastest bolt-action rifle of its day. The Lee Enfield rifles fire a 0.303 bullet. Note that the 0.303 bullet actually measures 0.311 inches in diameter, as we have noted previously.

The Indian Ordnance board later made a variant of this rifle called the Ishapore 2A1, which was based on the Lee Enfield Mark III rifle model.

The main difference is that the Ishapore 2A1 rifle is chambered to fire a standard NATO 7.62 x 51 mm. round. As a result of this, the steel used in this weapon is also improved to handle the higher pressures of the NATO cartridge. This rifle has the distinction of being the last bolt-action rifle designed to be used by a regular military force (other than sniper rifles, which are for special forces only). It is still used by police in various states in India. It is also popular with civilian shooters in the UK and USA.

The Lee-Enfield cock-on-closing-bolt system was also used on a number of other rifles, mostly made in the UK and other commonwealth countries.

A third variant is the Mosin-Nagant system, which was first used by the Mosin-Nagant rifle in 1895. Unlike the Mauser system, the bolt head rotates with the bolt and lugs, whereas the Mauser has the bolt head is an integral (non-removable) part of the bolt. It is also unlike the Lee-Enfield where the bolt head remains stationary and the bolt alone rotates. It is a rugged design, but is complicated. This type of bolt-action was mostly used in Russia, but one version called the M28 was manufactured by the Finns. The M28 is widely regarded as one of the finest and most accurate military rifles ever produced and was used by the most successful sniper of all time, a Finn named Simo Hayha.

There are other bolt-action systems, but never caught on as much as the above three systems.

Bolt actions are more accurate than semi-automatic rifles, which is why hunters and military snipers still use them. The reason is because when the cartridge is fired, the entire energy is devoted to propelling the bullet out of the rifle, unlike a semi-automatic or automatic weapon, where part of the energy is diverted to eject the old cartridge, auto-cock the weapon and load a new cartridge. It also has less moving parts than most other action types. The only parts that really move in a bolt-action when it is being fired are the spring and the firing pin. This simple and strong design means it can fire magnum cartridges as well. One more advantage for snipers is that it does not eject the spent round automatically, which is beneficial to the sniper because it does not give away his position and he can decide to eject the round himself when it is safe to do so. The only disadvantage is that it is slower to use than some other actions. So, while it may not be as useful to an ordinary infantryman, this action is more valuable to snipers and hunters and has thrived for these reasons even to the present day.

1 comment:

  1. I think your dates on the Mosin Nagant are a bit off.