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-   -   2" Barrelled AR (https://armslocker.com/showthread.php?t=60522)

Garand 03-14-2017 06:10 PM

2" Barrelled AR
 
[url]http://www.wideopenspaces.com/this-2-short-barreled-ar-15-will-shock-you/[/url]

Really this is a bit much, except for fighting in phone booths..........

BigBassMan 03-15-2017 06:09 AM

Melvin would be in heaven! Bragging about how quiet it is an the 1000 yard shots he would make! Small enough for spider hole fighting too!

Garand 03-15-2017 10:20 AM

With his bad back, I really want to see the size of the "spider hole" he can dig. Speaking of Melvin, I wonder if the reprobate has gotten himself thrown back in jail?

BigBassMan 03-15-2017 04:06 PM

I have not heard a word from him, unusual, will have to dig phone number out an call. Then listen to it all again for two hours.

Garand 03-17-2017 01:50 AM

ROFLMAO!

ethereal 03-18-2017 07:07 AM

Some people do stuff just to see if it works, or for the lolz.

The individual in question just wanted to see if it went bang repeatedly and what it chrono'ed at. Familiar with him from another group.

John in AR 03-18-2017 07:19 AM

First thing I wondered was "what velocity does it reach like that?", because it's more 'blowing the bullet out of the case' than anything else.

Second thing was "how does he make it cycle reliably with basically zero dwell time?" Thing likely has a gas port a quarter inch in diameter. The fact that it did cycle is impressive.

BigBassMan 03-18-2017 07:37 AM

There are certain people that should not be allowed near a firearm or a reloading bench. Like a old 1877 Colt Lightning black powder 38 long colt that had 38 spl. fired in it. Then he tried to make the springs an other parts, worked on it for about 5 years an then dropped it off on me the other day. No way to ever get it right again. Think I will drill a hole thru the frame an mount it on a walnut plaque an give it back with words to the effect " do not shoot this piece of **** again!"

ethereal 03-19-2017 01:15 PM

[QUOTE=John in AR;272242]First thing I wondered was "what velocity does it reach like that?", because it's more 'blowing the bullet out of the case' than anything else.

Second thing was "how does he make it cycle reliably with basically zero dwell time?" Thing likely has a gas port a quarter inch in diameter. The fact that it did cycle is impressive.[/QUOTE]

While I understand that the "quarter inch" is more of an expression, it can't readily be done with an AR sporting a 0.2235 nominal (0.2240 is mid-limit but oft quoted) groove; it'd depressurize slightly if it were larger than the groove diameter. I don't remember what it was exactly but I think it was at under the 0.125 nominal channel of a standard [I]gas block[/I].

As per dwell time, it's only part of the equation. You really don't need a ton of dwell time in an AR. Taking the problem from the top, what you need to cycle the weapon is, simplified, enough force to overcome the buffering system and stiction, with enough useful work left over to seat the carrier fully rearward against the spring's resistance. If and however you do that, aside from qualitative feel and component endurance, it'll "work." You increase wear on the extractor, especially, and can rip case heads, but similar logic is employed by most commercial manufacturers to reduce warranty or service returns to the general public; it's easier to throw more of an impulse at it and be less exposed to environmental variables or improperly spec'ed ammunition than size out everything to spec ammo and consider the weapon as a whole system (and expect customers to cater to that). Also, once the carrier key is off the tube all that dwell is doing is increasing wear on parts and possibly shooting more gas into the receiver set, many people don't like the feel of the dwell itself and that's how you get mid length 12.5's and rifle length 16s, which nonetheless work fine.

Even the journal diameter of the barrel, affecting when the full 0.125 gas block channel kicks in, is important to consider when choosing a gas port size due to pressurization and various theories pertaining to the physics involved with gasses.

ethereal 03-19-2017 01:44 PM

As an addition, less than 35% of the powder is probably being burnt at that length. Should be hitting something like 36k PSI at the muzzle by my numbers and the chamber never getting up to standard pressure.

I wonder if the proximity of the gas port to the muzzle actually creates a strange backpressure situation where what's in the tube tries to go to the outside air, exerting less force on the carrier key rearward.

It's a good thing that brass expands...


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