 MTNmyMag
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Posted: 9/13/2010 9:15:26 AM
consider this a tag
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Posted: 9/13/2010 9:49:33 AM
Instead of using a 16" barrel, why not use the barrel length that you want and pin on a barrel shroud extension. That way you can build it the way you want and have the gas system set up correctly in the beginning.
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Posted: 9/13/2010 9:58:39 AM
[Last Edit: 9/13/2010 10:04:36 AM by RDTCU]
Originally Posted By cookhj: Instead of using a 16" barrel, why not use the barrel length that you want and pin on a barrel shroud extension. That way you can build it the way you want and have the gas system set up correctly in the beginning. The tuning going from a 16" to an 11.5" won't be all that difficult, and i've already got a YHM 16" carbine 1:7 barrel. Even at 16", the OAL will be under 26" without a long flash hider... Unfortunately, the AR180 gas port/shoulder distance is about 1/4" longer than on an AR-15 barrel, so i either have to make a new gas block or turn the shoulder on the barrel back a bit, and i'm inclined to go with modifying the barrel, since the AR180 gas block is smaller and lighter than anything i can make on my bridgeport... plus i already have one in hand... Once i get it running, I'll probably send this barrel off to ADCO to have it shortened after the SBR stamp is back. |
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Posted: 9/13/2010 1:07:51 PM
[Last Edit: 9/13/2010 1:08:22 PM by RDTCU]
Just sent an "I'll take it" on the EE for one of these for $275 for this project, hopefully i was the first...
Trying to keep it small-ish... 
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Amontgomery
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Posted: 9/14/2010 6:39:14 PM
Originally Posted By JPN:
Originally Posted By RDTCU:
Here's the standard AR trigger-hammer pin locations relative to the grip. Yeahhh, it's kinda tight in there... Looks like the gas block would be more of a clearance problem than the barrel. 
A forward trigger group would provide a better feeling trigger, and simplify the design of the safety, but it looks like you don't have the space. I guess since the YHM bbl has already been ordered it is too late to back out of a 7" gas port. I would wonder about moving the gas block either rearward into a pistol length gas system or forward into a midlength system. If you moved it back the barrel itself could be turned down to a lightweight profile at least at the area near the trigger group. I would just be concerned with having too much pressure initially before having a chance to SBR it. Then again, you could always use a pistol cartridge blow-back operation and chamber it in 7.62Tok |
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Posted: 9/14/2010 7:01:56 PM
PDR = Personal Defense Rifle (rifle cartridge).
Blowback with a Tok takes out the design challenges, too easy
 As far as the barrel, i kinda wanted to start with existing barrels for cost reasons, and the SBR barrel will be ~11.5" so midlength is a bit long and pistol is too short... It will probably take some tuning, but once i SBR it, i will probably throw on a Gemtech TREK which will only add about 4" to the PDR and cuts out ~32 db... |
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Amontgomery
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Posted: 9/14/2010 9:08:31 PM
Originally Posted By RDTCU:
PDR = Personal Defense Rifle (rifle cartridge). Blowback with a Tok takes out the design challenges, too easy As far as the barrel, i kinda wanted to start with existing barrels for cost reasons, and the SBR barrel will be ~11.5" so midlength is a bit long and pistol is too short... It will probably take some tuning, but once i SBR it, i will probably throw on a Gemtech TREK which will only add about 4" to the PDR and cuts out ~32 db... Would the can add some pressure to make a middy work better? However you do it, judging by the gun in your avatar, I am sure it will be bad ass. |
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Posted: 9/14/2010 9:18:04 PM
Originally Posted By Amontgomery: Originally Posted By RDTCU: PDR = Personal Defense Rifle (rifle cartridge). Blowback with a Tok takes out the design challenges, too easy
As far as the barrel, i kinda wanted to start with existing barrels for cost reasons, and the SBR barrel will be ~11.5" so midlength is a bit long and pistol is too short... It will probably take some tuning, but once i SBR it, i will probably throw on a Gemtech TREK which will only add about 4" to the PDR and cuts out ~32 db... Would the can add some pressure to make a middy work better? However you do it, judging by the gun in your avatar, I am sure it will be bad ass. Probably, but i would like to be able to run it unsuppressed with a Levang comp or similar for minimum overall length.. I MIGHT be able to get it to run reliably with a middy.
It will be a piston gun using the AR180B piston. |
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Posted: 9/14/2010 9:21:01 PM
[Last Edit: 9/14/2010 9:22:20 PM by JPN]
Originally Posted By Amontgomery:
Then again, you could always use a pistol cartridge blow-back operation and chamber it in 7.62Tok Why blowback? 7.62Tok will cycle a pistol length DI gas system on a 16" barrel. If you dump the weights out of the buffer, it'll cycle on a 10" barrel. |
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Posted: 9/14/2010 9:24:26 PM
[Last Edit: 9/14/2010 9:35:54 PM by JPN]
Originally Posted By RDTCU:
Originally Posted By Amontgomery:
Originally Posted By RDTCU:
PDR = Personal Defense Rifle (rifle cartridge). Blowback with a Tok takes out the design challenges, too easy As far as the barrel, i kinda wanted to start with existing barrels for cost reasons, and the SBR barrel will be ~11.5" so midlength is a bit long and pistol is too short... It will probably take some tuning, but once i SBR it, i will probably throw on a Gemtech TREK which will only add about 4" to the PDR and cuts out ~32 db... Would the can add some pressure to make a middy work better? However you do it, judging by the gun in your avatar, I am sure it will be bad ass. Probably, but i would like to be able to run it unsuppressed with a Levang comp or similar for minimum overall length.. I MIGHT be able to get it to run reliably with a middy. It will be a piston gun using the AR180B piston. If I'm not mistaken, one of the dealers selling barrels is selling a 16" barrel with a rifle length gas system (very little barrel left in front of the gas block). I don't know if those barrels require anything more than a larger gas port to function reliably. ETA: It's a DPMS 16" heavy barrel with a rifle length gas system. Midway lists it as item # 724394. From the reviews, it apparently doesn't cause any cycling problems. |
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Posted: 9/14/2010 9:41:41 PM
[Last Edit: 9/14/2010 10:12:42 PM by RDTCU]
Yeah, i've seen rifle-length 16" barrels and i have a carbine-length 10.0" barrel on the pistol in my avatar, but how much barrel is left on a midlength 11.5" barrel?
I forget what the midlength port position is off the top of my head...
On my pistol, the vortex laps over the barrel about 0.05" and i cut the shoulder so that it bottoms on the shoulder only about .002-.003" before bottoming on the gas block, so it doesn't get much shorter than that... |
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Posted: 9/14/2010 9:58:48 PM
Originally Posted By RDTCU:
[div style='font-size: 8pt; font-family: Verdana, Arial, Helvetica; background-color: rgb(213, 212, 213); ']Yeah, i've seen rifle-length 16" barrels and i have a carbine-length 10.0" barrel on the pistol in my avatar, but how much barrel is left on a midlength 11.5" barrel? Taking a rough measurement off of my 18" midlength upper, a midlength 11.5" barrel would put the gas port about 2" from the end of the barrel. |
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Posted: 9/14/2010 10:03:11 PM
I happened to think of the gas tubes in my parts bin.
A midlength gas tube is 2" longer than a carbine gas tube. |
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Amontgomery
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Posted: 9/14/2010 10:08:28 PM
[Last Edit: 9/14/2010 10:11:19 PM by Amontgomery]
Carbine is 7", Middy is 9", and Rifle is 12".
I am curious to know if the suppressor would increase the pressure enough to make a middy more feasible than the carbine. ETA: I didn't see your response to mine earlier, though I am phrasing the question as purely theoretical now. Nothing saying you can't run the barrel out an inch or so more to make sure you have the clearance for a mount/brake as well. ETA: How long is your gas block going to be? |
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Posted: 9/14/2010 10:18:08 PM
Originally Posted By Amontgomery: Carbine is 7", Middy is 9", and Rifle is 12". I am curious to know if the suppressor would increase the pressure enough to make a middy more feasible than the carbine. ETA: I didn't see your response to mine earlier, though I am phrasing the question as purely theoretical now. Nothing saying you can't run the barrel out an inch or so more to make sure you have the clearance for a mount/brake as well. ETA: How long is your gas block going to be? Gas block is only 0.7" long, and i'll be turning the gas block shoulder on the barrel back 0.22" so that the gas port lines up. So yes, a middy would fit, but i'd be concerned with reliability as i'm in unknown territory on the AR180 piston and bolt, and the dual oprod/yoke that i've got drawn up will have a bit more mass than the AR180 op-rod. |
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Posted: 9/14/2010 10:28:29 PM
Originally Posted By RDTCU:
Originally Posted By Amontgomery:
Carbine is 7", Middy is 9", and Rifle is 12". I am curious to know if the suppressor would increase the pressure enough to make a middy more feasible than the carbine. ETA: I didn't see your response to mine earlier, though I am phrasing the question as purely theoretical now. Nothing saying you can't run the barrel out an inch or so more to make sure you have the clearance for a mount/brake as well. ETA: How long is your gas block going to be? Gas block is only 0.7" long, and i'll be turning the gas block shoulder on the barrel back 0.22" so that the gas port lines up. So yes, a middy would fit, but i'd be concerned with reliability as i'm in unknown territory on the AR180 piston and bolt, and the dual oprod/yoke that i've got drawn up will have a bit more mass than the AR180 op-rod. Opening the gas port to a larger size will make a difference. As I recall, my 7.62Tok barrels have the gas ports opened up to 0.120". |
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Amontgomery
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Posted: 9/15/2010 10:48:37 AM
Will you have a way of metering the pressure to the system?
I am unfamiliar with the AR180 and the piston system on it. If you had a trash bbl that you didn't mind messing up, you could always drill new ports and weld over the old ones until you found the optimum location then order a barrel with the gas-port drilled in the location you choose. |
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Posted: 9/16/2010 12:00:19 AM
Does anybody have a Levang comp they can measure? Length and diameter is all i really need... The one in my model was a best-guess as i don't have one...
Also, I wonder if the Gemtech Trek is right at 1.5" diameter as advertised or if it's a little over/under... |
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98snakebite
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Posted: 9/16/2010 12:15:54 AM
[Last Edit: 9/16/2010 12:17:23 AM by 98snakebite]
Originally Posted By RDTCU:
Does anybody have a Levang comp they can measure? Length and diameter is all i really need... The one in my model was a best-guess as i don't have one... Also, I wonder if the Gemtech Trek is right at 1.5" diameter as advertised or if it's a little over/under... The Levang is 1.995" in length and .918" in diameter. I am sure nominal is 2.000" x .920". |
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Posted: 9/16/2010 10:32:11 AM
If you would like a mid length gas tube in a carbine length, couldnt you get a pigtail gas tube and make it work? Or does a pigtail make a carbine change to rifle length?
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Posted: 9/16/2010 10:45:08 AM
Originally Posted By TenRingSS: If you would like a mid length gas tube in a carbine length, couldnt you get a pigtail gas tube and make it work? Or does a pigtail make a carbine change to rifle length? I think i'm trying to go the opposite direction that you think i am... Plus it's piston operated... |
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Posted: 9/16/2010 10:50:29 AM
Originally Posted By TenRingSS:
If you would like a mid length gas tube in a carbine length, couldnt you get a pigtail gas tube and make it work? Or does a pigtail make a carbine change to rifle length? This is going to be a piston gun, if I understand correctly, so gas tube length is irrelevant, except for port placement for the piston system. |
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Posted: 9/16/2010 11:02:20 AM
Duh me.....
I just got caught up in skimming over the gas tube convos and forgot you were going piston Im such a newb..... |
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buckmeister
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Posted: 9/16/2010 8:48:43 PM
Concerning the electronic trigger mentioned earlier: didn't the ATF rule all e-triggers were illegal ( too easily converted to full auto)?
Following this thread with interest. buckmeister |
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JoshAston
'Course, that ain't exactly Plan A
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Posted: 9/17/2010 12:02:04 AM
Originally Posted By TenRingSS: If you would like a mid length gas tube in a carbine length, couldnt you get a pigtail gas tube and make it work? Or does a pigtail make a carbine change to rifle length? Pigtail gas tubes are a gimmick anyway. Making the gas tube longer doesn't change where the gas port is. |
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