Gun Terms

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Ryan
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Gun Terms

Post by Ryan » Tue Aug 05, 2014 3:30 am

"Well gunnit, I’ve been seeing a lot of misused terms on here, and I figured I’d try to clear up some of the confusion. When attempting to correct people (politely mind you, at least at first), I have been met with plenty of arguing and a shower of down-votes. And this from a community that (rightfully) goes around correcting people on terms like ‘’clip’’ and ‘’assault rifle.’’ (If you're unclear on the definition of an assault rifle, I've defined it at length here.)You’re damn right I’m bitter, but not because I care about karma. I don’t care that I was down-voted; I care that this symbolizes that these errors are not simple mistakes that people are willing to correct, but instead people are accepting the false information being spread around by those who were arguing with me. Yes, I realize I sound arrogant, but bear with me here. Discussion is good. Don’t take what people say at face value without thinking for yourself, but at the same time, if you are uninformed on a subject, perhaps it is best to not argue your point with such a vengeance, without at least doing some research first. I will refrain (at least for the time-being) from linking to any of the aforementioned threads, in order to avoid singling anybody out.

The primary topics I intend to discuss are listed below. If you would like me to discuss any other topics, feel free to comment below or shoot me a PM. If you feel up to the task, write out your own explanation and I will edit it in to my OP (giving you due credit, of course), once we have agreed upon the facts.

Accuracy vs Precision

“Tolerances”

Felt Recoil vs Total Recoil

Loudness

Accuracy vs Precision

Accuracy for the actual machine that is your rifle is (basically) irrelevant. Yes, you read that correctly. Your rifle doesn’t need to be accurate, it just needs to be precise. Let’s define some terms:

Accuracy is how close the average result is to the intended result.

Precision is how close each result is to the others.

Poor accuracy is easily remedied by zeroing your sights properly. Precision is a result of your barrel, ammo, etc.

The only time accuracy would be relevant for a rifle is if the point of impact is so far out of line with the bore that you physically cannot adjust your sights far enough.

For the shooter, however, both accuracy and precision are important. 10 ‘’accurate’’ shots might make a pretty circle around your target, and 10 precise shots might kill the shit out of the tree next to your target. But neither of those are what you’re aiming for.

Personally, I don't really care if people misuse the term accuracy when talking about their rifle, as there's really only one thing they can be referring to, and that is that the rifle groups tightly. Even though that's not technically what they said.

“Tolerances”

I see this term thrown around a lot, especially here on /r/guns. It has a very specific meaning, and 99% of the time it’s used here, the person should be saying clearances.

Tolerances refer to the permitted variation from the intended dimensions of a completed part in a manufacturing process.

Clearances refer to the intended “space” between two parts, i.e. how well they fit together.

Allowances refer to the ‘’extra’’ material that is present after a step in a manufacturing process, in order to allow for later machining.

Your AK is not more reliable because it has higher ‘’tolerances.’’ High tolerances mean a poorly made firearm. Full stop. High tolerances means the manufacturer was unwilling to spend the money to ensure low variation and high consistency in their product. If your QC allows for a barrel diameter of .220 inches ± .0002 inches, then .0002 0.0004 (thank you /u/nnorton00 and /u/cawpin ) inches is your total tolerance.

Your AK is reliable because it has high clearances, i.e. larger spaces between parts which allow gunk, dirt, and the blood of fascists to build up without affecting the functionality of the firearm. If you have a 1.00 inch wide magazine than must fit into a 1.06 inch wide magazine well, then you have .06 inches of clearance between the two parts.

Lastly, allowances are basically how much extra material you have to allow for later machining. Say you want to thread a barrel. You need it to have a greater diameter than what the final inner diameter of the threads is going to be. If you want threads with an inner diameter of .500 inches, and an outer diameter of .505 inches, you better not make that barrel with an outer diameter of .502 inches, or you want have enough material to make the threads.

Recoil

Recoil essentially breaks down into two relevant topics – total recoil and felt recoil.

Force is the ability to make an object accelerate. How much it accelerates depends on the object’s mass. Force is what causes felt recoil.

Impulse is the total change in momentum of an object. Impulse is the total recoil.

The impulse imparted onto the shooter and his rifle is equal to the bullet’s muzzle velocity times its mass (plus the momentum that results from the expelled propellant gases - thanks to /u/TwoHands for this addition).

I=∆p=m*v

Where I is impulse, p is momentum, m is mass, and v is velocity.

You cannot change the impulse, given the same load fired out of the same barrel. It does not depend on the mass of the firearm or the mass of the shooter. You can have a manly steel butt plate, as found on glorious Mosin (which is, by the way, the rifle’s proper name, as all Nagant did was design the god damn magazine spring. His name is only used to refer to the rifle in the Western world) of Motherland, or a 5 inch thick rubber sissy pad (I guess I’m a sissy, because recoil pads rock). I don’t care. The impulse is the same. Unless you want to redefine physics and say that the Law of Conservation of Momentum is no longer valid, you cannot change the impulse imparted onto a gun by a bullet of a known weight and muzzle velocity. Nothing ‘’absorbs’’ recoil. The closest thing would be a muzzle brake, as this imparts some of the impulse onto the gases (which, of course, have mass) that are being expelled to the rear. Note however that the total impulse is the same, but some of it is being taken out of the system by those gases.

So what can you change? Felt recoil. This can be changed in two main ways: by spreading the impulse out over a longer period of time (we’re still talking hundredths of a second here) or by increasing the mass that the recoil is acting on.

The former follows the equation

I=F*t

Where I is once again impulse, F is average force, and t is the total time of ‘’impact.’’

Rubber butt pads are, in scientific terms, squishy, and serve to increase the time over which the rifle is smashing against your shoulder, thus reducing the average force and overall ouchiness of firing the gun. Another way to increase the time of impact would be to adopt a looser stance (with your body, not your grip. If you don’t hold the stock against your shoulder, it is going to hurt). In the same way that a boxer leans away from a punch to soften the blow, allowing yourself to lean back (as it’s firing, that is. I’m not referring to the infamous “chick lean”) with the gun will decrease felt recoil. You may have seen this in some videos of people shooting large bore rifles or shotguns. Bending your elbows has the same effect for handguns.

The second way of reducing felt recoil is by increasing the mass of the firearm.

F=m*a

Where F is still force, m is mass, and a is acceleration. A more massive gun will cause a lesser acceleration of the gun into your face than a lighter gun, simple as that. This is why shooting the 2’’ .357mag S&W airweight revolver that the RSO handed to you with a grin on his face on the first day you ever shot a gun feels like getting stabbed in the hand, whereas shooting the 6’’ .357mag S&W 686 next to it is rather pleasant, despite them both firing the same round. But I’m totally not speaking from personal experience, so make of that what you will.

Loudness

Well, fuck me. Due to large disagreements on the proper multipliers for loudness and power, I am going to remove the numbers from the first half of this section, since they were anyways only intended to serve as examples to further the general ideas. Instead they caused confusion. Thus, off with their heads!

(Thank you to /u/Szalkow for correcting me here. Loudness scales by a factor of 2 for every +10 dB, not a factor of 10. I was incorrectly talking about power.)

This topic I will only cover very briefly, as there’s really not much to say about it that relates to shooting. I won’t define any terms (except upon request) as most of them should be fairly obvious.

The scale used to describe the loudness of a sound is logarithmic, and uses the unit decibel, which is one tenth of a “Bel” and is shortened dB. What does it mean that it’s logarithmic? It means that instead of a linear system, where 110 dB would be 110% as loud as 100 dB, 110 dB is actually multiple times as loud.

A suppressor or ear plug that decreases the muzzle report by 30 dB is decreasing the sound by orders of magnitude. This is a big fucking deal. USE YOUR HEARING PROTECTION. ALWAYS.

The second and final point I will make on this subject is that sound decreases as a function of the square of the distance from the source. This means that if you are twice as far away as your friend is from the gun being fired, then it is ¼ as loud for you as it is for him. If you’re operating the weapon, your ears are probably about two feet from the muzzle if you’re firing a rifle with a long barrel. Consider that if you are firing an SBR, your ears may be up to twice as close to the muzzle, making the sound 4x as loud.

This has not taken into account the effect of muzzle brakes/compensators. Most of the sound from a gun without any muzzle devices is ‘’projected’’ forward. However, if you add a muzzle brake to your firearm, this is going to direct a large amount of the gases rearward, and the sound will go along with them.

So there’s my guide. If you find any errors, do make sure to let me know so that we can spread accurate information, instead of contributing to the problem of misinformation.

TL;DR I would say ‘’screw you this took me over an hour to write so read the whole damn thing,” but I want this information to be available to you, even if you have better shit to do than read five pages of techno-babble.

A good gun is precise. Accuracy for the gun comes from properly zeroing it. A good shooter is both accurate and precise (consistent).

If you’re saying your gun has high tolerances as though that’s a good thing, you probably should be talking about clearances.

Felt recoil is how much it hurts. Total recoil is how much it’s ‘’pushing’’ you. Felt recoil is easy to decrease with butt pads and heavier guns, total recoil is only really affected by muzzle brakes and mounts/bipods/tripods (none of these will truly affect the recoil, but they’ll direct it into the ground/air rather than the shooter).

Sound is measured on a logarithmic scale, not a linear scale. An increase in 10 dB is not slightyl louder, it is several times louder. Loudness decreases by the square of the distance from the gun, so standing 2x as far from the gun makes it 4x quieter, and 3x as far away makes it 9x quieter. Wear your goddamn ear protection.

Also, I didn’t save this until I finished writing it, and had a minor heart attack when I realized what could have happened." - http://www.reddit.com/r/guns/comments/1 ... me_of_the/.

A post on common misconceptions with gun terms.
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