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Pacs
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Posted: 1/26/2012 11:46:18 PM
[Last Edit: 1/27/2012 12:03:09 AM by Pacs]
WHY Not.



10.5" barrel with a carbine length gas system is dwell time about 90ms


14.5" barrel and carbine length gas system dwell time is about 206ms

16" barrel and mid length gas system dwell time is about 181ms

20" barrel on a rifle gas system dwell time is about 184ms



A 10.5" barrel on a pistol gas length dwell time is about 213ms


Why not use the pistol length gas system that falls in line with a nice about<200ms> dwell time instead of such a short 90ms?


Don't the 8" and 9" 300BLK barrels have pistol length gas systems?
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TheMercenary
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Posted: 1/26/2012 11:23:43 PM
Tag

This is a good question


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sweatpants
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Posted: 1/26/2012 11:30:24 PM
Tag for answers.

My gut tells me it was a legacy consideration.
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RussellAthletic
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Posted: 1/26/2012 11:37:32 PM
I've wondered the same thing before.
Pacs
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Posted: 1/26/2012 11:54:26 PM
Thinks for moving it to the correct forum. I think.
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regularAZguy
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Posted: 1/27/2012 12:22:11 AM
Originally Posted By TheMercenary:
Tag

This is a good question




interested....

jaqufrost
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Posted: 1/27/2012 12:33:58 AM
[Last Edit: 1/27/2012 12:38:10 AM by jaqufrost]
I think you might have issues with the pressure being to high for too long.

My 10" SBR with carbine gas has never failed. My 16" rifle with Rifle gas runs everything but Wolf and would probably run that if I opened it up a bit.

ETA: essentially your dealing with the volume of gas needed to run the system reliably. On a pistol gas system you have more pressure at the port, so less dwell time is needed and over-gassing can happen faster. If you wanted to run a pistol gas on a 10.5" barrel I would start with a small gas port, probably about .045 and work up from there.
jerz_subbie
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Posted: 1/27/2012 1:24:01 AM
Ironically, I was recently thinking about this after seeing pics of Spike's new barrels that they'll offer for their new suppressor line up.


Curios if anyone has tried this.
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RPM509
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Posted: 1/27/2012 3:01:13 PM
Interesting question and have wondered along the same lines myself on occasion, figured smarter minds than mine had prevailed before.

On a side not, aren't your estimated times way off the reality scale? 90 ms = 90/1,000 of a second. This being just quicker than 1/10th of a
second. That is retardedly slow for a bullet traveling just a couple/few inches.

2,800 fps = 33,600 inches per second
33,600 ips = 33.6 inches in 1/1,000 (1ms)
90ms = 3,024 inches...

my math messed up?
RDTCU
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Posted: 1/27/2012 3:06:16 PM
[Last Edit: 1/27/2012 3:13:09 PM by RDTCU]
1. Your math is off by 3 orders of magnitude, unless you mean MICROseconds, which is "µs"
2. It's not all about dwell time. The pressure is MUCH higher than with a carbine system (~50% higher), and with the longer dwell time, will make for a very harsh operation with standard pressure ammo...

Pacs
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Posted: 1/27/2012 3:40:18 PM
Originally Posted By RDTCU:
1. Your math is off by 3 orders of magnitude, unless you mean MICROseconds, which is "µs"
2. It's not all about dwell time. The pressure is MUCH higher than with a carbine system (~50% higher), and with the longer dwell time, will make for a very harsh operation with standard pressure ammo...

http://ar15barrels.com/tech/223plot.gif




yes I make Bo-Bo.

10.5" barrel with a carbine length gas system is dwell time about .090ms


14.5" barrel and carbine length gas system dwell time is about .206ms

16" barrel and mid length gas system dwell time is about .181ms

20" barrel on a rifle gas system dwell time is about .184ms



A 10.5" barrel on a pistol gas length dwell time is about .213ms


Why not use the pistol length gas system that falls in line with a nice about< .200ms > dwell time instead of such a short .090ms?

"Do not call attention to yourself and invite the man into your life" Bama-Shooter

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Phixeon
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Posted: 1/27/2012 4:46:12 PM
It might be a good idea if you want to run a suppressed rifle with Subsonics.
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RDTCU
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Posted: 1/27/2012 5:00:25 PM
Originally Posted By Pacs:
Originally Posted By RDTCU:
1. Your math is off by 3 orders of magnitude, unless you mean MICROseconds, which is "µs"
2. It's not all about dwell time. The pressure is MUCH higher than with a carbine system (~50% higher), and with the longer dwell time, will make for a very harsh operation with standard pressure ammo...

http://ar15barrels.com/tech/223plot.gif




yes I make Bo-Bo.

10.5" barrel with a carbine length gas system is dwell time about .090ms


14.5" barrel and carbine length gas system dwell time is about .206ms

16" barrel and mid length gas system dwell time is about .181ms

20" barrel on a rifle gas system dwell time is about .184ms



A 10.5" barrel on a pistol gas length dwell time is about .213ms


Why not use the pistol length gas system that falls in line with a nice about< .200ms > dwell time instead of such a short .090ms?



Regardless of dwell time, the VOLUME of gas that escapes through the gas port is what drives the bolt/carrier. The higher the pressure, the higher the flow rate.
Cole2534
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Posted: 1/28/2012 10:56:20 PM
[Last Edit: 1/28/2012 10:57:46 PM by Cole2534]
I don't see any reason the flow rate can't readily be reduced.

It seems that one could calculate the impulse required to reliably operate the action and work from there. Start on the small side and work up.

That said, I wonder if wear would manifest itself in new areas as a result of higher pressures and temps?

Also, are we dealing with a pure (relatively speaking) gas at this point, or some flaming two-phase flow?
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