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January 10, 2012 2:08 AM   Subscribe

Fundamentals Of Small Arms Weapons (Part Two, Part Three)
Ever wondered just exactly how repeating and automatic firearms operate? This 1945 U.S. Army training film will tell and show you the whole mechanism in-detail, complete with incredibly sweet hand-made models!
posted by teatime (44 comments total) 83 users marked this as a favorite

 
I really love these old educational films; they're often more informative than modern ones, and clearly a lot of effort went into their creation. This 1930 one about how differentials work is one of my favorites. The awesome models in these firearm mechanism vids really make me want to break out the AutoCAD and practice my engineering drawing and 3D modelling, though!
posted by teatime at 2:12 AM on January 10, 2012 [8 favorites]


That was intensely satisfying. Reminds me of the great old The Way Things Work book.
posted by Erasmouse at 2:44 AM on January 10, 2012 [3 favorites]


Oh wow, Erasmouse... that was my favorite book as a kid! I recently bought my sister's kids the updated edition of that, The New Way Things Work, as well as his The Way We Work (which has amazing illustrations of biological stuffs).
posted by teatime at 2:54 AM on January 10, 2012 [2 favorites]


This whole Youtube channel is pretty sweet.
posted by louche mustachio at 3:25 AM on January 10, 2012 [1 favorite]


Back when they educated people, rather than merely telling them facts.
posted by DU at 4:20 AM on January 10, 2012 [5 favorites]


It also shows you why it is trivial for a machinist to convert pretty much any legal semi-automatic rifle into a fully-automatic weapon. It's not rocket science. Unfortunately.
posted by three blind mice at 5:00 AM on January 10, 2012 [4 favorites]


Unfortunately? What's so particularly unfortunate about that?

Are full-auto firearms inheriently more dangerous or more "scary" than semi-auto ones?
posted by teatime at 5:19 AM on January 10, 2012


... here's hoping I didn't just derail my own thread.
posted by teatime at 5:20 AM on January 10, 2012


If fully-automatic weapons are worse than semi-auto ones, and it takes a machinist to do the conversion, the US should be pretty safe. Unfortunately.
posted by DU at 5:26 AM on January 10, 2012 [9 favorites]


Fully automatic guns tend to be less accurate than semi-automatic (due to recoil) for most untrained shooters, but that doesn't make them any less scary.
posted by Burhanistan at 5:29 AM on January 10, 2012 [1 favorite]


Are full-auto firearms inheriently more dangerous or more "scary" than semi-auto ones?

I actually wrote out a paragraph or two specifically stating why this is not the case but thought it would be far too boring/gun-porn-y for Metafilter. But essentially a semi-auto firearm is as or more dangerous than a full-auto one given it's accuracy when firing single vs. multiple shots.

If I were target shooting or tactical/sport shooting with a weapon capable of autofire I'd still stick to 2-3 round rapid singles rather than use burst or automatic settings. Give me the job of suppressing an enemy position or denying a specific area to an OPFOR infantry squad and I'll have a SAW/GPMG please. Individual targets? Stick to singles.

Back on topic (sorry for addressing the derail!) - has anyone seen a video of the rotating breech of H & K's G-11 prototype? Amazing technology designed in the late 60s and only finally getting a decent production chance as part of the new US LSAT project. It's a fascinating solution to a problem and one of many technical innovations possibly coming into play in the next generation of military firearms.
posted by longbaugh at 6:10 AM on January 10, 2012 [3 favorites]


The problem with automatic rifles or handguns isn't that they make it more likely to hit the shooter's target, but less likely, while sending more bullets into unintended targets. In modern armies, no-one but trained machinegunners shooting on a dedicated mount or bipod uses full-auto in actual combat. Even three round bursts are on their way out.

Remember, Gun Control isn't about the no-fun brigade taking away neat toys, it's about making it difficult for organized crime to equip private armies with weapons that cause immense collateral damage in heavily populated locations (Like cities. Or schools.)

That said, with extensive training and licensing, I think anyone should be able to own any sort of gun they like if they use and store it responsibly... but they need to be held accountable (with jail time and civil suits) if their weapon is stolen and used in a crime, or sold to an irresponsible third party.
posted by Slap*Happy at 6:17 AM on January 10, 2012 [4 favorites]


Yeah... totally derailed my own thread... and I knew better, too :(
posted by teatime at 6:23 AM on January 10, 2012


Also, DU - sorry to depress you further but you certainly don't need to be a machinist with access to a machine shop to change a semi-auto weapon to full auto. Australian F1A1s and British L1A1s (both semiautomatic variants of the FN FAL) could both be easily modified to fire full auto with judicious use of a file. Australian SAS used cut-down F1A1s converted to full-auto in the jungle and I've even heard of one enterprising British soldier who used a matchstick to mess with the sear during the Falklands War. Now I mention it - the Argentines did use full-auto FAL variants but their troops were mostly conscripts with poor weapon maintenance so even though both sides had virtually identical base weapons I'm not sure you can really illustrate the autofire vs. semiauto argument there even.

And now - I shall run away before it is derailed further.
posted by longbaugh at 6:26 AM on January 10, 2012 [2 favorites]


The Gunny's guru always said "Here's hoping your enemies are on full auto"
posted by 445supermag at 6:30 AM on January 10, 2012 [2 favorites]


Now I kind of want to make one of these awesome models.
posted by RustyBrooks at 6:36 AM on January 10, 2012 [3 favorites]


RustyBrooks: Right? I want to make an animation of one, but probably will never get around to it.
posted by teatime at 6:39 AM on January 10, 2012


That video is a model of clarity. I've been shooting guns my entire life, including cleaning and disassembling them, and I had several "ah ha!" moments watching that. Neat stuff.
posted by Forktine at 6:50 AM on January 10, 2012 [1 favorite]


The film is pretty interesting ... in part because, at least to my knowledge and in my experience, nothing like that is shown anymore. At least it wasn't when I went through BCT and qualified on the M16A2. The explanation during the BRM evolution of how the '16 worked was pretty much on the level of "you pull trigger, weapon go boom, gun get dirty, you clean weapon."

Although that was a very basic BRM / qual course; maybe the training that the old films were designed for was something more advanced to begin with.

Relevant to the derail: one demonstration that I do remember, though, was showing how quickly you can unload a magazine, even on the 'A2 (which does not have FA, it's semi and 3-rd burst). One of the instructors basically bump-fired it, and went through 30 rds in about 2 seconds, which I think is actually faster than FA on the 'A1 would have been. In retrospect I'm not totally sure why they felt it necessary to demonstrate that particular ability, since it did nothing but tempt a lot of morons into trying to figure out how it was done.
posted by Kadin2048 at 6:54 AM on January 10, 2012 [1 favorite]


I have no interested in guns whatsoever, but I found these videos extremely satisfying.
posted by Pendragon at 7:15 AM on January 10, 2012 [1 favorite]


They didn't explain direct impingement.

Which is good, because it sucks.
posted by the man of twists and turns at 7:46 AM on January 10, 2012 [3 favorites]


What makes these so good (and the rear diff one too) is that they start from the very basic thing and build it up... so each step is actually really simple. The whole seems complex, but when it is done you understand why each additional complication is necessary, and what exactly for.
posted by Meatbomb at 7:51 AM on January 10, 2012 [3 favorites]


Hey, thanks for this. It's really great. I've fired guns before but never have I seen such a lucid explanation of exactly what was going on inside the gun. DU nails it above, this educated me on the subject in an extremely satisfying way.
posted by word_virus at 8:07 AM on January 10, 2012 [1 favorite]


Reminds me very much of those physics-based build-a-contraption games. I'm going shooting this weekend for the first time since, damn, Boy Scouts, so the post's timing is excellent!
posted by MrMoonPie at 8:15 AM on January 10, 2012 [1 favorite]


They didn't explain direct impingement.

It was basically experimental at the time -- there was the French MAS-40, but it was limited service only, and the Swedes had a rifle that used it, the AG m/42, but to the US Army, it simply didn't exist, so it wasn't worth mentioning.

Which is good, because it sucks.

It can be reliable, and it is lighter that regular gas operated, but yeah, dumping the combustion gases into the receiver is really not the best idea in the world.
posted by eriko at 8:15 AM on January 10, 2012 [1 favorite]


Fascinating stuff.

These videos had me flashing back hard to my old expository writing classes. It is much harder than most people think to thoroughly, and cogently, explain processes. These films do it perfectly.
posted by Benny Andajetz at 9:13 AM on January 10, 2012 [1 favorite]


They didn't explain direct impingement.

Which is good, because it sucks.


IS SAME AS RIFLE SHITS WHERE HE EATS.
posted by adamdschneider at 9:44 AM on January 10, 2012 [4 favorites]


Also, DU - sorry to depress you further but you certainly don't need to be a machinist with access to a machine shop to change a semi-auto weapon to full auto. Australian F1A1s and British L1A1s (both semiautomatic variants of the FN FAL) could both be easily modified to fire full auto with judicious use of a file. Australian SAS used cut-down F1A1s converted to full-auto in the jungle and I've even heard of one enterprising British soldier who used a matchstick to mess with the sear during the Falklands War. Now I mention it - the Argentines did use full-auto FAL variants but their troops were mostly conscripts with poor weapon maintenance so even though both sides had virtually identical base weapons I'm not sure you can really illustrate the autofire vs. semiauto argument there even.

I think most people reading this thread now, but modifying a semi-auto weapon to full automatic fire-even accidentally-is a very serious felony in the US. People have been successfully prosecuted for having a semi-auto weapon that went full auto by a mechanical malfunction. BATFE is noone's friend.

Modifying any civilian legal semi automatic available in the US currently is not a trivial task. (the military models may be different-I am not a certified amorer). There are differences in several parts that most be modified that go beyond a "few minutes with a file". BATFE actually examines weapons for this before allowing them for sale on the 'open' market. Some actions are easier than others to modify. A recoil operated, open bolt (such as the m3 submachinegun)is trivially easy to modify for full auto. This is the reason this style of action is not available on the civilian market and replica weapons that resemble this style have to be changed to a close bolt style of operation.

Modifying a gas/recoil action to full auto is very difficult for anyone but a good gunsmith. It is easy to file down the sear so it will empty the magazine the first time the trigger is pulled, but you can't stop the firing by releasing the trigger reliably. It also causes a 'hair trigger' on the fire are so that unintentional discharge is a real danger. All the parts they add on the third film have to be added to the action and made to work to a very fine tolerance during rapid and violent cycling. I own a civilian legal FAL rifle and the bolt, hammer and sear would all have to be replaced and the reciever modified with drilling and welding to make it 'select fire'-the action style were you can flip a switch between safe, semi, and full auto fire-which i have no intention or ability to do.

BTW these films are excellent and I have never seen a better explanation for the why modern smokeless, repeating firearms function. Good post.
posted by bartonlong at 10:36 AM on January 10, 2012 [3 favorites]


People have been successfully prosecuted for having a semi-auto weapon that went full auto by a mechanical malfunction

This sounds dubious... Care to cite a case?
posted by DavidandConquer at 11:12 AM on January 10, 2012 [1 favorite]


They didn't explain direct impingement.

Which is good, because it sucks.


that's an opinion, and one not shared by everyone.

if anything, DI is an attempt at refining the self-loading process by basically positing that the fouling incurred is merely paper tiger compared to the benefits gained in weight savings and long-range accuracy.
posted by DavidandConquer at 11:19 AM on January 10, 2012 [1 favorite]


Here is the Wikipedia entry

Olafson

It is just one case that I know of, but still scary. BATFE gives a whole new meaning to 'capricous and arbitary' enforcement of regulations that they largely determine themselves than won't define for anyone, until trial and then define to make sure they get a convinction.
posted by bartonlong at 11:36 AM on January 10, 2012 [2 favorites]


I've always wondered about the mechanics of semi/full auto reloading. These were extremely clear and nifty videos. Thanks a bunch for satisfying years old curiosity!
posted by TheCoug at 11:38 AM on January 10, 2012 [1 favorite]


@bartonlong--thanks. that is truly disturbing.
posted by DavidandConquer at 12:38 PM on January 10, 2012


Excellent post, thanks for this.
posted by Daddy-O at 2:06 PM on January 10, 2012 [1 favorite]


DavidandConquer, it was my understanding that the weight savings of DI aren't really about the total weight of the rifle, but rather reducing the moving weight, and thus the center of mass. Making re-acquiring the target for followup shots much easier. Following with the straight-line stock and massively offset sights (was the AR10 the first to do that?), the rifle, to me, seems more designed for recoil control and multi-shot performance. Good things in a combat rifle (and I love the M4), but I'm still not a fan of DI.

/also, never thought I'd get into a DI vs. gas piston discussion on MeFi.
posted by the man of twists and turns at 2:29 PM on January 10, 2012 [2 favorites]


@the man of twists and turns: yes, you definitely reduce the moving weight w/ DI but you are also minus the weight of the entire piston assembly, which is why piston ARs are invariably heavier than DI ARs. add to that the fact that a DI gun has less-finiky barrel harmonics and you get (what I believe to be) an ingenious solution that puts the soldier in charge of his rifle (ie, keep it clean and it'll be as accurate as a bolt gun) instead of the rifle's specs dictating the limits of the soldier...

and i agree that this is the last place I'd have expected to be discussing this :)
posted by DavidandConquer at 3:09 PM on January 10, 2012 [1 favorite]


Twists: Supposedly the Johnson LMG was the first gun fielded in large numbers to use a straight line stock.

I add "In large numbers" because in these sorts of discussions there seems to always be some limited production mutant prototype gun that had whatever feature being is discussed first.
posted by Grimgrin at 4:20 PM on January 10, 2012 [1 favorite]


I. NAMING OF PARTS

To-day we have naming of parts. Yesterday,
We had daily cleaning. And to-morrow morning,
We shall have what to do after firing. But to-day,
To-day we have naming of parts. Japonica
Glistens like coral in all of the neighboring gardens,
And to-day we have naming of parts.

This is the lower sling swivel. And this
Is the upper sling swivel, whose use you will see,
When you are given your slings. And this is the piling swivel,
Which in your case you have not got. The branches
Hold in the gardens their silent, eloquent gestures,
Which in our case we have not got.

This is the safety-catch, which is always released
With an easy flick of the thumb. And please do not let me
See anyone using his finger. You can do it quite easy
If you have any strength in your thumb. The blossoms
Are fragile and motionless, never letting anyone see
Any of them using their finger.

And this you can see is the bolt. The purpose of this
Is to open the breech, as you see. We can slide it
Rapidly backwards and forwards: we call this
Easing the spring. And rapidly backwards and forwards
The early bees are assaulting and fumbling the flowers:
They call it easing the Spring.

They call it easing the Spring: it is perfectly easy
If you have any strength in your thumb: like the bolt,
And the breech, and the cocking-piece, and the point of balance,
Which in our case we have not got; and the almond-blossom
Silent in all of the gardens and the bees going backwards and forwards,
For to-day we have naming of parts.

--Henry Reed, 1942
posted by storybored at 8:07 PM on January 10, 2012 [6 favorites]


which is why piston ARs are invariably heavier than DI ARs.

And why the Armalite AR-10 and AR-15 went DI, because the entire point of the weapon was to reduce the load of the rifle, so that load could instead be carried in ammo. Several studies after WWII that the US Army conducted came up with two facts.

1) The average combat range was less than 50m

2) The single accurate predictor of enemy casualties was rounds fired. Training didn't matter, round type didn't matter, if you fired more X, you hit more Y, so if you want a more effective infantry rifle, you want to fire more X.

Thus, the entire point of the AR-15/M-16 and the .223 Remington/5.56NATO round. In 10 kilos, you could carry 280 rounds in M14 7.62NATO clips, or 660 rounds in M16 5.56clips. More rounds = more effective infantryman.

This continues with the M4 Carbine which is now become the basic weapon of the US Infantryman -- and weighs less than 7 pounds *with* a full 30 round clip installed -- 4.5 pounds less than an M14 with a 20 round clip. It's shorter, arguably too short for the round, because that makes it quicker to point at the enemy -- because it's all about sending rounds at the enemy, and the more you can send, the better off you are.

Indeed, the biggest problem with the AK-47 wasn't the round -- the 7.62x39mm round it fired wasn't much heavier than the 5.56x45mm NATO round, but the weight of the magazines, which weighed almost a kilogram each when loaded. This is why the USSR went to the AK-74, firing 5.45x39mm rounds -- from polyethylene clips, which made the thing lighter than the current M4, and about two pounds lighter than a loaded M16.

And, since they didn't have to carry three extra pounds in the rifle, they could carry three extra pounds in ammo -- which works out to close to 150 rounds in an M4 or AK-74M.

And, thus -- more rounds fired.

I do think a big mistake in NATO was adopting the US 5.56 round (actually, the exact NATO round design came from Belgium) but this was a whole bunch of politics. The Brits accurately diagnosed the problem after WWII, realized that there .303 British (7.7x56mm -- this was a big cartridge) was way too much, and designed the .280 British (7x43mm) It's just a tiny bit heavier and a bit larger than 5.56NATO -- you'd get 26 rounds instead of 30, but the ballistic and terminal performance of the round was just better in every way. But, when they first proposed it, we insisted on 7.62, and when we did studies saying that this round was just too big, we kept them secret from the Brits, then dumped the 5.56 on them.

This all came back when the USSOC started asking for rifles chambered in 6.8mm Remington (6.8x43mm) and the Brits went "WE BUILT THAT ROUND 50 YEARS AGO, FOR FUCKS SAKE", then proceeded to smash a glass into USSOC's face and set fire to their car.

Okay, that last part is an exaggeration, but only just.
posted by eriko at 8:29 PM on January 10, 2012 [10 favorites]


Right at 7mm seems to be the sweet spot for ballistics. I wonder if anyone has crunched the numbers to figure out why that is? Something to do with the ogive and the viscosity of air, maybe.
posted by the man of twists and turns at 3:46 AM on January 11, 2012


I first want to say it is really, really great to have a non controversial/political technical gun discussion on metafilter. Guns are amazing pieces of technology really and deserve to be admired on purely asthetic grounds.

Right at 7mm seems to be the sweet spot for ballistics. I wonder if anyone has crunched the numbers to figure out why that is? Something to do with the ogive and the viscosity of air, maybe.

There are several variables that determine this. For a individual weapon system (meaning 1 man can carry the weapon and enough ammunition to be useful on a battlefield) the sweet spot seems to be between 6.5mm and 7mm. It allows a very effecient use of powder-the cartridge case can be kept short and lightweight while still carrying enough propellant to get the projecticle up to about 2400-2800 fps. At this speed a projectile needs to weigh about 120-140 grains to carry enough energy out to 400 yards to cause serious wounding/death. Now we get into the world of external ballistics which has everything to do with aerodynamics. If this projectile weight is used in a smaller bore than about 6.5mm this leads to a very long bullet that is hard to stabilize.
(A quick aside-the current trend in 5.56mm-or .22 caliber-military projectiles is to increase the weight from about 55 grains to upward of 65 grains which does lead to a more lethal projectile but you have to spin the projectile so fast to stabilize the longer round that it might come apart in flight, so you built a stouter bullet which is more expensive and doesn't deform as well on impact-so you make it heavier still to carry more energy and so on-you end up chasing your tail and you get slower and slower muzzle velocities since you asking the same amount of propellant to move a bigger mass and this lowers the rounds effectiveness and range and it gets worse fast as you make the barrel shorter, such as the current m4 carbine)
Anyway the shape you get from a 6.5-7mm bullet that weighs about 140 grains is just about as ideal as you can get in a small package as far as aerodynamics go so it doesn't slow down very fast and carries a lot of energy out to a far distance so you don't need insane muzzle velocities to get enough energy at 400 yards to do some damage. BTW i use a 6.5x55 swedish mauser(invented for the swedish military more than 100 years ago) or .260 remington (which ballistically duplicates the swedish mauser)when hunting deer for this reason.

The .30 caliber sweet spot where you get good ballistics is 165-180 grains and really carries way more energy than you need for man sized targets under 400 yards. And even with extensive training most people can't hit a man sized target beyond 400 yards so what is the point of equipping the average rifleman with such a weapon really? (it took close to 80 years for the US military to figure this out-the myth of the fronteir rifleman dies hard in the US). The .30 and larger calibers are very well liked and used in machine guns and sniper rifles which can make use of the longer range potential. In reality the next really great, effecient sweet spot for something a man can handle weight and recoil wise seems to be around 8mm to .338 caliber. This is a really populer caliber size for large (elk/red deer and non dangerous african game)
posted by bartonlong at 9:41 AM on January 11, 2012 [2 favorites]


From what I understand is the experience in both Viet Nam and Iraq, larger rounds are much better at penetrating light cover - dense vegetation in the jungle; cars, doors, walls and masonry in Iraq.

The shots-per-infantryman is predicated on the experience of the US infantry in WWII and Korea - which fought mostly in the open, with little effective cover apart from widely spaced trees and foxholes, and moreover, with giant honking .30-06 rounds that would breeze through what cover there was.
posted by Slap*Happy at 12:40 PM on January 11, 2012 [2 favorites]


This is amazing, the thought that has gone into that model is incredible, absolutely brilliant.
posted by marienbad at 12:50 PM on January 12, 2012 [1 favorite]


Great films, teatime. Thanks for posting.

I had no idea there were so many springs in small arms. They reminded me of the key action in a piano for sheer complexity.
posted by benito.strauss at 8:48 PM on January 28, 2012


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