The AR Is Not Direct Impingement

Direct impingement is where the gas bled from the barrel is fed through a tube to strike the face of the bolt carrier, causing it to move to the rear and open the bolt. As far as I am aware, there have only been two production designs that used direct impingement: The French MAS 49 and Swedish Ljungmans AG m/42 (which spawned the Egyptian Hakim and Rashid).

You can see in the Ljungmans patent drawing that gas will travel down the tube (10) and strike the bolt carrier at (12).

In the AR system the gas is fed inside the bolt carrier through the gas key. There is an expansion chamber inside the carrier. With the bolt closed, the rear of the bolt is inside this chamber. When gas enters the chamber it forces the bolt out. Since the bolt cannot go forward because it is held by the rear of the barrel, the bolt carrier goes to the rear.

The rear of an AR bolt is really a piston!

The confusion between these systems stems from the gas tube being placed in-line with the bolt carrier. Gene Stoner's original prototypes had the gas tube running along the left side of the rifle and entering the expansion chamber through a hole in the side of the bolt carrier.

Things That People Ignore

The M16, M16A1, M16A2, M16A3 and M16A4 have 20" barrels.

Colt made several carbines based on the M16 series with 10-14.5" barrels for military service. So far, only the M4 has gotten wide issue.

Where did those carbine barrel lengths come from? The 10" barrel comes from the old Colt R607, the first carbine they offered. This is basically placing the gas port where the pressure curve has dropped to the point where it's just barely safe to open the bolt. Since the front sight base is common with the M16 and they left room for threads for a flash-hider it dictates the 10" length.

The 10" barrel was not very reliable because the pressure dropped very quickly once the bullet had passed the gas port. Colt introduced a 3.5" blast moderator to help with both the flash and to increase back-pressure for more reliable function. While it helped with the blast, further flash reduction and reliability was desired, so a 4.5" slotted moderator was introduced. This was carried over into both the XM177 and XM177E1.

Reliability was improved, but more "dwell", the time between the bullet passing the gas port and exiting the barrel, was needed. The M16 had 4.5" more dwell than any of the early carbines. Increasing the barrel length to 11.5" and using the 4.5" moderator made the XM177E2 even more reliable. Unfortunately, the Vietnam war ended and the funding for the project mostly dried up. Some issues were never resolved entirely.

Where did 14.5" come from? If you took the barrel that extends from the front of the front sight base on an M16 and put it in front of a front sight on a carbine, you have a 14.5" barrel. It is reasonably reliable and can accept an M16's bayonet; which the XM177E2 cannot. It also ends up being about 5/8" shorter than an 11.5" barrel with a 4.5" moderator! The SEALs adopted this 14.5" carbine; Colt called it the R653. The Philippines even manufactured them.

All of these guns used the same M193/M196 5.56x45mm ammunition that the M16 and M16A1 used. It was noted as far back as Vietnam that the shortened barrels had a dramatic effect on the effective range. Since the R607, and XM177 series were issued primarily to special warfare troops where the short length and lighter weight combined with different tactics from the infantry compensated for the lack of range.

The M16A2, M16A3, M16A4, M4 and M4A1 use M855/M856 ammunition.

Like the M193, the M855 was designed with a 20" barrel in mind. Like the R607, XM177 series and R653, performance dropped because of the reduced muzzle velocity from losing 5.5" of barrel. The shorter weapon was definitely handier for riding around in the back of a Bradley and the lack of long range was not a factor in urban environments.

Like so many times in the past, we ignored that the war we just fought, or the conditions we are currently encountering, will not be the environment of the next war or even engagement; thus the M4 became the primary issue service "rifle" for the Army. The Marines retained the M16A2 and adopted the M16A4. The current conditions in Afghanistan are screaming for something hard hitting with long range and even the Marines are having some issues reaching out to the ranges required. The M14 in 7.62x51mm has made a triumphant comeback in these conditions.

Will we abandon the M16 platform altogether for a 7.62x51mm rifle? Will we change the caliber of the M16 and M4 to something with a bit more reach? Will we develop something completely new? Will we look back at the rifle developed for the conditions in Afghanistan right now and wish we still had the M4?

EDIT
By they way: the 16" barrel we see on civilian versions of the carbines comes from a legal requirement.

Big Boy Blog

This _IS_ my blog, dammit!

I really don't see how Livejournal is different from Blogger, Blogspot or others in the main. I can't post a blog-roll in the margin is just about the only difference I can see.

What makes a Blogger or Blogspot blog superior to this one?

I really don't see what makes those other methods better than this one. Perhaps Weer'd can explain, he's made the change recently.

Update 28APR17

This was imported from Livejournal, before I moved my posts here to Blogger.

Maybe I Have Found Something To Say

t is the president's duty to stand his ass at The Tomb of the Unknown Soldier and place the wreath on Memorial Day.

The current president intends to shirk this duty onto his vice-president.

As much as I disliked Clinton, he still did the duty.

Nothing Much

I think I am going to let the lights burn out here. I find that I just don't have much to say about much anymore and the things I do say, I have said before.

Fascinating

I note that the same congress members who supported the assault weapon ban in 1994 are the same congress members who say we need a new ban to stop the drug violence in Mexico.

Dianne Feinstein
Dick Durbin
Chuck Schumer

Not a comprehensive list, but it's always the same few people. The justifications change, but the solution doesn't.

Going Out On A Limb

I detest the militarization of the police. I cannot express my distaste enough.

I do not bow to the argument, "If we save even one cop's life..."

Bullshit!

When he's on duty he is The State. And The State has a vast supply of individual officers. Yes, a police officer is a person, with rights. As such, his rights should be identical to mine, since I am a person too.

The laws we are wrapping around the cops is making me a second class citizen with regards to many rights.

Conceal carry comes with the badge in most places, in particular in places where a normal citizen is not allowed to carry at all.

Self defense laws are far more lenient on the police than on common folks; especially so when you consider that a cop is typically put on paid leave while the shooting is investigated and legal counsel is provided by the department. The investigations are typically very cursory and are conducted by the police force itself as if it's impossible for it to have no interest in the outcome.

Speaking of self defense, I know when I can shoot a normal assailant. It's codified in the law and confirmed by jurisprudence. When can I shoot a cop? In theory, it's the same as any other assault. In practice, it's never legal. In some jurisdictions, it's possible for a cop to shoot almost as many people as he'd like with impunity.

The police are the ultimate in "circle the wagons" and band together groups.

How many times have you seen a cop flagrantly breaking traffic laws?

The police are people, just people. On average no better (or worse) than the rest of us. I dislike the pedestal we've made for them.

I detest the militarization of the police forces. Heck, I detest it's called a police FORCE. I'm of the opinion that if a cop needs an M113A2 APC to do the job then we need the Army to make the arrest (and the Army doesn't arrest people). We might discover that the cops don't need tracked armored vehicles if they cannot have them.

What about cops lives? What about them? As agents of the state, there are plenty more where they came from. The state can afford the losses. Any argument about a cop needing a piece of military equipment applies just as fully to me in regards to my safety. Ban me from having something, you don't get it either. Being a policeman should not be a path to elevation above the people he's been hired to protect.

I would feel a lot better if the rules the cops followed were the same as the rules I have to follow. They really aren't too onerous.

Here comes the narrowest part of my limb.

I feel that, as agents of the state, the infractions committed by the police should be punished more harshly than if the same thing had been committed by a normal citizen. That's not just an individual violating your rights, that's the agency and government violating your rights.

I have some token solutions.

Police uniforms will be distinctive from military in color and cut. While a cop on a SWAT team might need something very much like BDU's or ACU's a pair of dark blue coveralls will do.

If a cop shoots someone; instead of paid leave they get six months where they don't collect a penny from any government source, including unemployment. That tells me, emphatically, that the officer needed to pull the trigger. If the police unions want to pay his salary while he's suspended, let them. A private citizen who has to defend themselves with lethal force is subject to more, actually, after losing time to court appearances, costs of legal fees, stress, etc...

Again, if the cops need military hardware and training to get the job done, then it's obviously a military job not a police job. Full. Stop. I think that once we take away the cool tactical hammer then not every problem will be a nail.

In my threeperish moments I have to think that the first ones to be shot will have to be the local police. They will be the first ones sent to quell an insurrection. The gun community had better get happy with the idea that it's not going to be the faceless ATF ninja at the forefront of this, but the local police. Thoughtlessly supporting the police in every situation is being mindless. They are people, just like you.

Please note, this is not a call to start shooting the police.



Comments

Take Note

Go here. Scroll down to pic 13.

http://www.boston.com/bigpicture/2010/05/vietnam_35_years_later.html

I want you to take note that the soldier on the right is holding a hand gun by the barrel. His handgun is in its holster. The soldier on the left is holding an AK, not an issue item for the ARVN. Notice also that the prisoner is not wearing a uniform. These firearms were taken from him moments before the picture was taken.

Pic 14 is the famous one.

Under both Hague and Geneva persons found under arms and out of uniform during a time of war in a combat area can be summarily executed. That was exactly what General Nguyen Ngoc Loan did.http://en.wikipedia.org/wiki/Nguyễn_Ngọc_Loan

I really despise the "suspected Viet Cong officer" in the caption. It doesn't matter. Found under arms, out of uniform is all that does. If we started being less generous about the application of this rule, we might find that we will be more successful against a people who respect this form.

By the way, it is brutal. I agree. C'est la guerre.

Home Improvements Continue Apace

We finally got the last crank window in the house replaced with nice double glazed single hung windows. There is already a noticeable difference in temperature in both The Boy's and our bedrooms.

Window removed.

Marv remembered to wear his work boots.

Marv brought up his air compressor and air-hammer. It made short work of the grout that was surrounding the opening. For previous installs we had used hand chisels and hammers. That took hours; this took minutes. Figures we'd learn how to do it right on the LAST window.

It's in!

Computer Stuff

Way back in Oct 2007 I bought The Lovely Harvey a spiffy new 15" MacBook Pro (2.4 GHz). This was a twin to mine that I had bought in May 2007.

The video on mine failed in May of 2008 just days before its warranty expired. Apple repaired this machine, but thanks to the repeated warnings of possible data loss and up to 90 day turn-around on repairs I ended up getting a new machine (just in case) too. Three day turn around, no data loss. "Well, at least we have a spare," I thought.

Good thing we did. In February ago The Lovely Harvey's laptop died exactly like my first one did. Since we were well out of warranty there was much despair; but since we had the spare...

Her machine would fire up in target disk mode so I could transfer the data from her machine to the spare. I did a fresh install of OSX 10.5 onto the spare and then moved her stuff over. Simple.

The old machine got tossed into the closet until we had the $500-$900 to fix it.

Fast forward to yesterday.

I was talking with Anglave about his ancient work laptop and joked around that he should just get a new one. Ha ha. I then suggested a Mac, you know even more money he didn't have. Then I suggested he fix our broken one since the repairs were almost the same as a new Win7 machine. He expressed doubt that those price comparisons were correct, surely a logic board would be more.

So I googled to find some prices for logic boards and found:
http://www.xlr8yourmac.com/feedback/MacBookPro_video_failure.html

That led to
http://support.apple.com/kb/TS2377

Whereupon I discovered that the repair would likely be covered for free.

It is now 8 PM. There is an 8:40 appointment slot at the Genius Bar available 37 miles away. To the Jalopy! Triple digit speeds were achieved several times and the Escort 8500 paid for itself at least three times. I made it to the Apple Store with minutes to spare.

The Genius™ ran a diagnostic and confirmed it was the GPU. He then gave me a receipt, warned of data loss and slow turn around and all will be well.

Side Note: Coming out of the Apple Store I picked up a tail. Two thuggish looking guys were loitering outside the entrance to the store and followed me back to the car. They broke off when they saw that I was alert, looking at them and had my hand in my pocket. And by "broke off" I mean they did a 180˚ and went back into the mall.

Additional Side Note: The Genius™ got a kick out of my "I'm Not Carrying A Concealed Firearm (Or Am I?)" t-shirt. The charitable side of me would like to think that the thugs just wanted to read my shirt and having done so went back to loitering.

Quote Of The Random Interval

Small bullets may expand to create bigger holes, but large bullets don't shrink.

AKsarben posting on the 6.8 forums. http://68forums.com/forums/index.php