My New Toy [Complete]

wswartzendruber · Posted: Fri Nov 09, 2012 9:15 pm Post subject:

The story to far: Picture

BoneKracker · Veteran Joined: 14 Mar 2006 Posts: 1488 Location: U.S.A.

Where's the bolt, charging handle, and lower receiver group? Is that all there is to the stock, or is there a piece missing?
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wswartzendruber · Posted: Sat Nov 10, 2012 4:53 am Post subject:

That's all there is to the stock on a carbine. The bolt carrier group is in the mail, possibly lost. It's overdue. The lower receiver group is being held for ten days per California law. All the parts that go in the lower receiver are in the bag. I have some armory work ahead of me. I even had to buy special tools.

pjp · Posted: Sat Nov 10, 2012 5:15 am Post subject:

sikpuppy · Posted: Sat Nov 10, 2012 5:28 am Post subject:

BoneKracker · Veteran Joined: 14 Mar 2006 Posts: 1488 Location: U.S.A.

wswartzendruber · Posted: Sat Nov 10, 2012 7:11 am Post subject:

It's a background check (I think) and a cooling-off period.

notageek · Posted: Sat Nov 10, 2012 7:18 am Post subject:

Should you be worried?
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wswartzendruber · Posted: Sat Nov 10, 2012 7:42 am Post subject:

Nope.

pjp · Posted: Sun Nov 11, 2012 5:04 am Post subject:

lol @ cooling off period. Because someone who wants to react while "hot" is going to order a lower receiver to do the job. A .38 Special can be had cheap and w/o a check, so if someone really wants to do the job... hooray for lolgov.
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wswartzendruber · Posted: Wed Nov 14, 2012 7:24 am Post subject:

So yeah, it really does look like the bolt carrier group got lost in the mail.

BoneKracker · Veteran Joined: 14 Mar 2006 Posts: 1488 Location: U.S.A.

wswartzendruber · Posted: Thu Nov 15, 2012 7:07 am Post subject:

Actually, all I need to do is keep the ejection port cover open and finger a round in the chamber. All I'll have to do then it smash it with a metal pin.

wswartzendruber · Posted: Tue Nov 20, 2012 1:57 am Post subject:

I built the lower receiver today, and pieced the main portions together. It suffered one ding.

BoneKracker · Veteran Joined: 14 Mar 2006 Posts: 1488 Location: U.S.A.

So what will be done about the lost bolt carrier group, etc.?
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wswartzendruber · Posted: Tue Nov 20, 2012 2:23 am Post subject:

I'll be depressed about it until I decide to put out the money for a new one, or until it magically shows up in the mail.

dmitchell · Posted: Tue Nov 20, 2012 2:25 am Post subject:

What's a bolt carrier group?
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wswartzendruber · Posted: Tue Nov 20, 2012 2:26 am Post subject:

The bolt carrier group holds the round in place while it goes off. The round travels down the barrel, causing a pressure build-up. This new pressure ends up traveling down a gas tube that causes the bolt to unlock, move back, eject the old casing, and chamber a new round. It's the main moving part of the weapon.

dmitchell · Posted: Tue Nov 20, 2012 2:31 am Post subject:

Clever design. Thanks!
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BoneKracker · Veteran Joined: 14 Mar 2006 Posts: 1488 Location: U.S.A.

Nice drawings of bolt (1) and bolt carrier group (2-4), easy to understand:
http://www.behance.net/gallery/BOLT-CARRIER-GROUP-PROJECT/4197729

Exploded diagram of bolt carrier group:
http://www.ar15.com/content/guides/parts/boltCarrier.gif

Nice photograph of apparently poor quality bolt carrier group disassembled to operator maintenance level:
http://sgcusa.com/images/supporting_images_large/LMT_Enhanced_Full-Auto_Bolt_Carrier_Group_L7Q3_B.jpg

Exploded Diagram of AR-15 (complete disassembly):
http://ompldr.org/vZ2RrNw

The AR-15 design sucks (or maybe it was the specification) in my opinion. It's an unacceptable trade-off of reliability for reduced weight. The weapon overall is an excellent design, but the direct-impingement gas-operation mechanism, specifically the interface between the gas tube and gas key are entirely unacceptable, in my opinion.

A normal gas-operated weapon uses the exploding gases from within the barrel, just before the bullet exits it while they're still under high pressure, vented through a tiny hole in the barrel, to drive back a rod-like piston, which pushes the bolt assembly (in this case called the "bolt carrier group) back against a spring, which temporarily collects and stores that kinetic energy as potential energy, and then releases it again as kinetic energy, driving the bolt back forward, etc.

The AR-15 is a special type of gas-operated weapon that uses "direct impingement" (which I say sucks). Instead of pushing back a rod, the gases themselves travel through the gas tube all the way back to the receiver, where they are imparted to the bolt carrier group, blowing into the "gas key" (which is that smaller tubular thing you see screwed onto the top of the bolt carrier), pushing back the bolt itself. This design innovation eliminates entirely the need for any gas piston and housing, reducing the weight substantially. As one might imagine, heavy-ass weapons are a major complaint of infantrymen, so this is a heavily-weighted requirement.

The problem with the direct-impingement design is that those hot gases from the exploding round end up venting right into the upper receiver, which soaks up or burns off lubricating oil and coats all the parts with nasty carbon and corrosive by-products of the propellant which are very hard to clean off and can accumulate dangerously. This is why AR-15 variant weapons jam in heavy firefights, right when you absolutely don't want them to be jamming.

The design should be re-worked to either:

a) somehow vent the gases outside the receiver (and hopefully away from the operator's face, given that they undoubtedly are not the healthiest stuff to be breathing); or

b) utilize a short-stroke gas piston which eliminates most of the weight but still maintains separation of the propellant gases from the receiver.
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wswartzendruber · Posted: Tue Nov 20, 2012 4:43 am Post subject:

There are aftermarket piston mods for the AR-15 platform. There isn't consensus on if it's worth it, though.

To the weapon's credit, there is the forward assist that Colt decided was a definite necessity. For whatever reason, Armalite didn't include it.

BoneKracker · Veteran Joined: 14 Mar 2006 Posts: 1488 Location: U.S.A.

Yeah, just what you need in a firefight. A forward assist. I'd rather have a weapon that didn't have a tendency to jam if you put a few hundred rounds through it in a short time. It's still a great weapon, but I think it needs an integral, thoroughly-tested short-stroke gas piston. I didn't know there were such modifications available, but I wouldn't trust my life to an un-proven mod so central to the weapon's basic operation.
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Oldthinkers unbellyfeel INGSOC.
-- Headline of a document on Winston Smith's terminal in his cubicle at the Ministry of Truth, seen briefly in the background in one scene of the movie rendition of Nineteen Eighty-Four.

wswartzendruber · Posted: Tue Nov 20, 2012 5:50 am Post subject:

How do those things respond to sand? From my perspective, it's another moving part that needs regular cleaning maintenance.

BoneKracker · Veteran Joined: 14 Mar 2006 Posts: 1488 Location: U.S.A.