Basic Anatomy: Bolt Action Rifle

Mosin Nagant 91/30
The bolt action rifle dates back to 1824, and has remained very popular in the hunting and target shooting markets. Because of their strength, they can fire very large or high pressure calibers. Because of their simplicity, they can be easily broken down and maintained in the field, making them a prime choice for hunters. Target and competition shooters rely on bolt action rifles for their incredible accuracy potential.

Today, we’ll be learning about the basic parts that combine to form a bolt action rifle, using that pinnacle of Russian engineering, the Mosin Nagant 91/30. These rifles were first manufactured in 1891, and were fielded to Russian soldiers through World War 1 and 2. They are renowned as being nearly indestructible, 100% reliable under the worst of conditions, and, since literally millions of them were produced during WW2, easy to find and cheap.


FIELD STRIPPING

Mosin Apart

Yes folks, that’s all it takes to field strip most bolt action rifles. Remove the bolt and magazine (whatever form that might take) and you have ready access to all parts of the rifle. This is all you have to do in preparation for cleaning and regular maintenance. From here, we can see the largest and most basic pieces that make up this rifle. They are the bolt, receiver, stock, magazine, barrel, trigger, and sights.


The stock of a bolt action rifle is the main point of contact between the rifle and it’s user. A well-designed stock is crucial to sight alignment, and therefore accuracy. In technicality, the stock of a bolt action rifle is the carrier for the barrel and firing mechanism, designed to be held to the shooter’s shoulder when firing. The Mosin’s stock is a piece of extremely strong laminated wood, but many other types of stock exist made of synthetic materials and even metals.

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Let’s get a better look at the other important parts of this rifle.


RECEIVER

A rifle’s receiver (also called the action) is where all of the moving parts meet, where cartridges are picked up by the bolt, loaded into the chamber, fired, and ejected. It is, incidentally, where all of the action happens. Here’s a top view of what the Mosin’s receiver looks like:

 BMM_9961From this view it’s much easier to see the function of this part. The bolt slides in from the rear, where the screw is. Just right of that, in the bolt channel, is the sear, a small part critical to the rifle’s function. The sear is attached to the trigger. It holds back the firing pin when the rifle is cocked. Upon pulling the trigger, the sear lowers, allowing the firing pin to punch forward and set off the round.

Moving further to the right, you can see the magazine well. This is where the rounds rest before being loaded into the chamber by the bolt. At the far right of the picture is the beginning of the chamber. During the firing cycle, as you push the bolt forward, it picks up a round from the magazine well and pushes it into the chamber. The bolt locks in place, sealing the chamber while the bullet is fired, ensuring all the pressure from the explosion goes down the barrel.

Also worthy of note are a couple definitions. The muzzle, as we’ve previously discussed in other posts, is the end of the barrel which the bullet exits after being fired. It is generally the furthest point on a weapon from the shooter. At the other end of the barrel resides the breech. The breech is the end of the barrel into which rounds are loaded, and technically includes the chamber. Most, if not all, bolt action rifles are breech-loading firearms, meaning rounds are loaded into the rear of the barrel. The antithesis of this would be a muzzle-loading firearm. Revolutionary war era rifles are an example of muzzle loading weapons.


REAR SIGHT

I make mention of the rear sight because it incorporates a special feature. Rifle cartridges are designed to be effective out to much further ranges than pistol or shotgun cartridges. Basic external ballistics teaches that gravity begins to pull a bullet down the moment it exits the barrel. What this means is that a bullet doesn’t travel in a straight line, rather, it travels in an arc called a ballistic trajectory. At extended ranges, in order to hit your target, you have to technically aim the barrel up in order to accommodate for bullet drop or elevation. In order to do this accurately and consistently, the rear sight is adjustable for elevation. Looking closely at the rear sight, you’ll notice a sliding tab at the back. This is able to slide forwards and backwards, which raises or lowers the sight to adjust for firing at different ranges. Adjustability for elevation is a critical factor in rifle iron sights.


TRIGGER

Every firearm has a trigger, but a common feature you’ll find on rifle triggers is the ability to adjust the pull weight, which is the measure of how much rearward force on the trigger is required to disengage the sear. A lighter pull weight is a desirable trait for match and target shooters. There is a lesser chance of disturbing the rifle’s position when less force is required to actuate the trigger, which enhances accuracy potential.


MAGAZINE

The Mosin Nagant incorporates a fixed magazine, as do many other popular rifles. Rounds are loaded from the breech and pushed down into the magazine well. The picture above shows the floorplate released, which would allow the rounds to empty from the bottom of the magazine. Detachable box magazines are also extremely common, which are the same in function as pistol magazines. Round capacity for bolt action rifles usually hovers between 4-7 rounds, though there are box magazines with a higher capacity.


BOLT

BMM_9962

The bolt is the most important part of a bolt-action rifle. It completes the firing mechanism, in fact, the bolt alone could be called the firing mechanism of the weapon. The Mosin’s bolt is comprised of 6 separate pieces of machined metal. The bolt handle is the knob protruding up from the bolt. This piece is what the shooter grasps to manipulate the bolt. Running the length of the bolt is the firing pin, which screws into the rear piece of the bolt. There is a spring contained in the center of the bolt that the firing pin holds compressed upon cocking the weapon, and it provides the forward motion necessary to slam the pin into the cartridge primers to set off rounds.BMM_9963Here you can see the firing pin protruding from the bolt face. At the very front of the bolt you’ll see two metal protrusions that look like shark fins. Those are locking lugs, and they serve to lock the bolt into the breech when the firearm is in battery. If there weren’t any method of locking the bolt to the receiver, it would fire out the back of the weapon when you pulled the trigger!


A bolt action rifle is an great investment for any shooter. They offer great room to grow, with a huge variety of calibers and designs, as well as aftermarket parts. There’s a rifle out there for every shooter, and for every purpose. Mosin Nagants in particular are fantastic weapons to own. I find the history of the rifle incredibly interesting, and knowing there’s probably nothing I could physically do to the rifle to get it to fail is soothing to my “ruggedness above all else” mentality.

In the following weeks, we’ll begin discussing rifle specific stance and firing fundamentals, as well as delving into the basics of external ballistics. Until then, have fun, stay safe, and shoot straight!

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One thought on “Basic Anatomy: Bolt Action Rifle

  1. My brother collects guns as a hobby. He uses words like stock, receiver, and bolt quite a bit. I never knew exactly what he was talking about, so thanks for explaining! I can see why the stock is important for aiming like you said. Without it, it would be hard to keep the gun steady.

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