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| | |-+  New Gas Valve available for purchase
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Author Topic: New Gas Valve available for purchase  (Read 9488 times)
thehun
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« Reply #60 on: May 23, 2018, 10:50:50 AM »

Let's hope this fixes the problems...I truly hope it does...agreed that it should be a standard part on all rifles
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Sdevante
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« Reply #61 on: May 23, 2018, 10:58:32 AM »

Mine is arriving today and will go to the range this weekend. Also hoping this fixes the problem - although the thought has occurred to me that if this is not a standard part on the 5.56, then I suppose I either need to buy another extra valve or constantly switch valves when switching calibers. What a PITA. Thanks DT!
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Articlion
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« Reply #62 on: May 23, 2018, 11:31:51 AM »

fyi "all new rifles are shipped with the  3 position gas valve which is what the rifle was designed for"(DT). The 6 position valve is just an accessory (just like hanging dice from your mirror it looks cool but does nothing for performance and cost you money ) that is not needed or required to make your rifle operational or reliable. so if you want to look cool sticking a screw driver down your hand guard go ahead and buy the latest flavor of cool aid from DT but don't think that  by installing the valve you will fix cycling rim ripping syndrome on your new rifle. Your best bet would be to use the warranty and send the rifle back the DT. The  warranty department seems on the up and up and are addressing problems quickly and professional they should get your rifle running as designed. with out having to buy anything
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thehun
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« Reply #63 on: May 23, 2018, 11:33:06 AM »

Mine is arriving today and will go to the range this weekend. Also hoping this fixes the problem - although the thought has occurred to me that if this is not a standard part on the 5.56, then I suppose I either need to buy another extra valve or constantly switch valves when switching calibers. What a PITA. Thanks DT!

Well your gas port sizes will be different for a 5.56...so this plug won't work anyway on the 5.56 MDR...
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AF Gunner
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« Reply #64 on: May 23, 2018, 01:37:08 PM »

fyi "all new rifles are shipped with the  3 position gas valve which is what the rifle was designed for"(DT). The 6 position valve is just an accessory (just like hanging dice from your mirror it looks cool but does nothing for performance and cost you money ) that is not needed or required to make your rifle operational or reliable. so if you want to look cool sticking a screw driver down your hand guard go ahead and buy the latest flavor of cool aid from DT but don't think that  by installing the valve you will fix cycling rim ripping syndrome on your new rifle. Your best bet would be to use the warranty and send the rifle back the DT. The  warranty department seems on the up and up and are addressing problems quickly and professional they should get your rifle running as designed. with out having to buy anything

I actually agree with you; however, They should be shipped with the same quality and workmanship as the 6 position. Mine works fine with the 3 position but I wanted more choices mostly for shooting suppressed. Which I have not done yet. I'm sure the 3 positon will work fine for thousands and thousands of round with that welded insert. But they just look like s*** and are not of the quality you expect from a $2500 dollar gun. If they get rid of the welded insert on the 3 position, fine keep shipping them. I would also say they should convert new guns to the new detent just for compatibility between the 3 and 6 valve and not having as many parts to inventory and mix up in production.
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Sdevante
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« Reply #65 on: May 23, 2018, 01:41:32 PM »


Well your gas port sizes will be different for a 5.56...so this plug won't work anyway on the 5.56 MDR...

Excellent point I had not thought of.
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EODBombtechnician
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« Reply #66 on: May 23, 2018, 11:23:55 PM »

Mine is arriving today and will go to the range this weekend. Also hoping this fixes the problem - although the thought has occurred to me that if this is not a standard part on the 5.56, then I suppose I either need to buy another extra valve or constantly switch valves when switching calibers. What a PITA. Thanks DT!

Well your gas port sizes will be different for a 5.56...so this plug won't work anyway on the 5.56 MDR...

Yup, the new plug is stamped 308.
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thehun
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« Reply #67 on: May 24, 2018, 08:22:29 AM »

fyi "all new rifles are shipped with the  3 position gas valve which is what the rifle was designed for"(DT). The 6 position valve is just an accessory (just like hanging dice from your mirror it looks cool but does nothing for performance and cost you money ) that is not needed or required to make your rifle operational or reliable. so if you want to look cool sticking a screw driver down your hand guard go ahead and buy the latest flavor of cool aid from DT but don't think that  by installing the valve you will fix cycling rim ripping syndrome on your new rifle. Your best bet would be to use the warranty and send the rifle back the DT. The  warranty department seems on the up and up and are addressing problems quickly and professional they should get your rifle running as designed. with out having to buy anything

I actually agree with you; however, They should be shipped with the same quality and workmanship as the 6 position. Mine works fine with the 3 position but I wanted more choices mostly for shooting suppressed. Which I have not done yet. I'm sure the 3 positon will work fine for thousands and thousands of round with that welded insert. But they just look like s*** and are not of the quality you expect from a $2500 dollar gun. If they get rid of the welded insert on the 3 position, fine keep shipping them. I would also say they should convert new guns to the new detent just for compatibility between the 3 and 6 valve and not having as many parts to inventory and mix up in production.

Agreed...no matter how a company ships out a rifle...it should function 100% without a hitch at this price point.
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Blackandwhiteknight
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« Reply #68 on: May 29, 2018, 01:09:44 AM »

Being new to piston guns I had to do some google research on the subject.  I found some interesting things that helped shed light on the MDRs woes.  Piston veterans if i missed something please chime in.

  Short version, looks like this new gas plug may fix the cycling issues with the MDR.  Second, this is not an upgrade, its a fix to a problem DT new about (and probably created another one in the process).

  Okay here goes. Being a DI AR guy I'm familiar with the gas port size and location being used to adjust the timing of the system, in conjunction with the weight of the carrier/ buffer.  Turns out in a Piston gun that is less important and much more hinges on the piston assembly itself.   The concept of increasing the gas to add more energy to the cycle is pretty straight forward, but what I found interesting is the adjustment of the piston chamber itself.

 I ran into a post on an M14 forum about adjusting the timing on the iconic system that made me think.  The gist of it is that the dwell time of a piston system is regulated by how fast the piston chamber fills with gas to propel the piston.  The more you open up the gas port the faster you fill the chamber.  The interesting part is that by increasing the chamber volume you are effectively slowing the time it takes to fill it, creating more dwell time.  One of the posts mentioned that the smaller the chamber the more sharp and violent the recoil impulse tends to be.  Ring a bell?

 Speaking of dwell time. I just went shooting yesterday and while my brother was shooting the MDR with some M80 I was watching the bolt cycling.  As I was watching the port in the ejection chute I could literally see flash and sparks coming from the fired cases as they where pulled from the chamber.  I've shot a lot of guns and I've never seen that before.  Another observation I have made is that when the gun is clean there is very little, if any damage to the rims (1k rounds on my gun).  When it is dirty and hot is when I start getting torn rims.  If the cases are literally being pulled before the burn/ dwell is complete this would make sense. When the chamber is clean they pull out, when its caked with carbon they stick, and the rims take the heat.

  Chamber dwell time is influenced by several things, including the weight of the projectile, and the charge and burn rate of the propellant among other things.  Lets assume whoever did the engineering math behind the dimensions had a decent starting point.  So the general size of the piston components, bolt carrier ect should work on paper... within a know pressure spectrum.  It's seems likely that the production MDR was given out for testing and people started shooting ammo other than DT match ammo through it, which is where the problems started.

 Which brings us to the gas plug sleeve.  Now taking what we already know about the gas piston chamber, if you put a sleeve in the plug you have reduced the chamber volume, and in turn the dwell time.  There are two possible trains of thought about this problem. #1 DT knew about this change in volume and compensated by reducing the port size accordingly.  This one seems a little unlikely given MDRs current performance.  #2 DT completely spaced it and significantly handicapped the MDRs gas system for a quick cheap "fix" to an over pressure issue with ammo other than DT match.

 I find it interesting the ES tactical cut straight to the chase and custom ported a 6 position plug for their barrels.  That raises the question of who came up with the idea first, ES tac, or DT?  Also makes me wonder if ES tac expanded the chamber volume over what DT started with.

  Either way this brings me to my last point, this 6 position plug should have been in the MDR when it was released.  Pretty obvious DT knew something was wrong when they put the sleeve in there. It's a blatant band-aid.  Sleeve the plugs and ship the guns, we'll get the new plugs when we can.

  DT needs to own this and make good with it's customers.  Don't tell us the turd sandwich (welded plug) was designed that way.  Admit it was a temporary fix, and say you're going to make it right.  Free of charge.
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GoShort
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« Reply #69 on: May 29, 2018, 08:01:58 AM »

So your saying DT over gassed the MDR by having the gas ports too large in an effort to fix it they sleeved in some smaller ports shifting the problem to being too small a gas chamber instead of too large a gas port. Keeping the same issue just shifting it to a different source.
If I had not spent $2500 on an MDR this might be a bit funny. I wonder if the could resolve it be sending out replacement 3 position gas valve with the right size holes, and no sleeve.

And thanks for the great explanation

Sent from my Nexus 5X using Tapatalk
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Sawdustshot
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« Reply #70 on: May 29, 2018, 09:23:20 AM »

I was guessing the chamber was too small/ holes too big. Depending on how far of a push the op rod needs, I wonder if the piston could be shaved down in length to give more volume. Would 1/16-1/8" fix or reduce the issues?
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Whoops
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« Reply #71 on: May 29, 2018, 01:29:11 PM »

I was guessing the chamber was too small/ holes too big. Depending on how far of a push the op rod needs, I wonder if the piston could be shaved down in length to give more volume. Would 1/16-1/8" fix or reduce the issues?

You're gonna get increased recoil due to the deceased weight, and it'll beat on your rifle a little harder I think.

So far the biggest suspects for why the MDR is unreliable seem to be the following:
1. Barrel extension
2.gas chamber/ports
3. The firing chamber
4(?). Possibly the extractor is too small.

Basically, the design itself seems to be fine, but due to some QC issues and some small things that should have been caught, they all act together to.make the MDR function to an iffy degree at best.

When I get my MDR I plan on joining in this beta testing process but we'll see how it goes. I'm more than a little irked because all I wanted was a solid .308 bullpup that had the features I wanted- the MDR got all the features right IMO, but didn't get the solid part right.
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JesseJames38
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« Reply #72 on: May 29, 2018, 02:08:12 PM »

In the words of my friend from work.  They had everything going for it.    "They got the ball, ran it all the way to the one yard line and spiked it."    In short,  they just didn't make it to the goal line to spiked the ball, they came up one yard short and blew it.  And sadly, they have all the opportunity to make it right, and they fumbled that to.       GOO TEAM!
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thehun
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« Reply #73 on: May 29, 2018, 04:35:02 PM »

 Popcorn Popcorn Popcorn
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TNC
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« Reply #74 on: May 29, 2018, 09:00:50 PM »

BlackandWhite, some of your assessments appear quite logical, and your description is very good.  I wonder about the carbon fouling or buildup you mention.  Piston guns like this are renowned for taking a very long time to build up carbon and residue in the chamber...obviously they eventually get dirty...just run cleaner than DI's and such.

That is interesting about your observation of possible combustion at the ejection port.  Can't say I've seen or heard of it before.  It caused me to go look at some semiauto and full auto vids that show closer shots of the ejection port.  I looked at quite a few and never saw flame or sparks.  I'm certainly not saying that can happen, as I certainly haven't seen or heard everything.

Being a reloader my understanding is that all combustion has occurred before a spent case is extracted from the chamber.  In a piston gun the case swells completely preventing the initial combustion blast from going into the barrel extension or ejection area.  Most flame and other combustion byproducts go out the muzzle with some small gas amounts still following the spent case as it ejects from the chamber.  A blown primer or catastrophic case head failure could result in flame or sparks in the barrel extension and ejection port area, but it would seem most unusual otherwise.

Just observations on my part, so take that for what it's worth.
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Sawdustshot
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« Reply #75 on: May 29, 2018, 11:55:11 PM »

You're gonna get increased recoil due to the deceased weight, and it'll beat on your rifle a little harder I think.
If the piston shaft's small diameter is .250" and I did my math right, the weight reduction from shaving .125" off the end is a whopping 0.028 ounces. However, moving the piston face back that same distance increases the chamber volume by what, 10 percent on the low end? The relative increase in chamber volume is far greater than the relative decrease in the weight of the reciprocating parts.
« Last Edit: May 29, 2018, 11:56:59 PM by Sawdustshot » Logged
GoShort
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« Reply #76 on: May 30, 2018, 03:43:52 PM »

So I watched and re-watched with plenty of pausing and resuming the DT gas valve video.
what I was trying to see is how far in the the back edge of the gas valve  the hole/s are.
what I cannot see (someone with an MDR could enlighten us) is how far in from the back edge the gas chamber goes. I was trying to figure out how DT may be able to fix some of the issues without a major redesign of any parts.
my thought if the gas pressure/timing is an issue and taking into account info from previous posts. what if they just moved the holes towards the mussel a bit on the barrel/valve/block. since I do not know the math let say 1/8th inch.
I do not know if the holes on existing barrels/gas blocks/valves could be filled so they could be reused (sounds like a bad ideal) but it seems it would be relatively easy to move the holes in newly created ones.
if the hole is moved toward mussel a small amount on existing barrel/block/valve design you can skip
   moving barrel shoulder
   moving gas block
   redesigning gas block to accommodate shift of pic rail from moving block
   extending the piston
Going forward you can correct
   gas block hole size
   gas valve hole sizes
   barrel hole size
   not sleeve new valves
What will moving it forward do? (if my thinking is correct)
   1)more expansion time in barrel before gas is released into gas block so pressure lowers  going into gas block
   2)more time for casing to stop expanding
   3)since hole sizes are corrected lower pressure in gas chamber
   4)no longer having a sleeve in the gas valve expands the gas chamber again lower pressure
   5) 1, 3, 4 should all contribute to lower pressure and stop rim ripping?
   6) 1, 4 should effect timing allowing casing to not stick?
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thehun
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« Reply #77 on: May 30, 2018, 04:22:17 PM »

Love the enthusiasm...but honestly...if someone is going to go buy a $2500 rifle...DIY their way into trying to solve a design flaw...it should be a hint that the platform is not worth it and has some major flaws.
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kfeltenberger
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« Reply #78 on: May 30, 2018, 08:35:10 PM »

So I watched and re-watched with plenty of pausing and resuming the DT gas valve video.
what I was trying to see is how far in the the back edge of the gas valve  the hole/s are.
what I cannot see (someone with an MDR could enlighten us) is how far in from the back edge the gas chamber goes. I was trying to figure out how DT may be able to fix some of the issues without a major redesign of any parts.
my thought if the gas pressure/timing is an issue and taking into account info from previous posts. what if they just moved the holes towards the mussel a bit on the barrel/valve/block. since I do not know the math let say 1/8th inch.
I do not know if the holes on existing barrels/gas blocks/valves could be filled so they could be reused (sounds like a bad ideal) but it seems it would be relatively easy to move the holes in newly created ones.
if the hole is moved toward mussel a small amount on existing barrel/block/valve design you can skip
   moving barrel shoulder
   moving gas block
   redesigning gas block to accommodate shift of pic rail from moving block
   extending the piston
Going forward you can correct
   gas block hole size
   gas valve hole sizes
   barrel hole size
   not sleeve new valves
What will moving it forward do? (if my thinking is correct)
   1)more expansion time in barrel before gas is released into gas block so pressure lowers  going into gas block
   2)more time for casing to stop expanding
   3)since hole sizes are corrected lower pressure in gas chamber
   4)no longer having a sleeve in the gas valve expands the gas chamber again lower pressure
   5) 1, 3, 4 should all contribute to lower pressure and stop rim ripping?
   6) 1, 4 should effect timing allowing casing to not stick?


Muzzle, not mussel.

Look at the SCAR and you'll see a gas block set relatively far back from the muzzle and closer to the chamber, so the concept is sound and works.  I think there are other issues at play than where the gas block is located on the barrel.
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Kurt
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« Reply #79 on: May 30, 2018, 09:23:44 PM »

I thought that spelling looked off but autocorrect so i left it.

Sent from my Nexus 5X using Tapatalk

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