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Bullpup Rifles (Auto & Semi-Auto Centerfire) => Desert Tech MDR => Topic started by: Blackandwhiteknight on June 12, 2018, 11:47:52 PM



Title: .308 MDR Ejection chute (fixed)
Post by: Blackandwhiteknight on June 12, 2018, 11:47:52 PM
  The MDR ejection chute in it's stock condition poses reliability issues do to snags and drag on the cycling system.   These snags of soft brass on steel obviously cause case damage, which leaves brass shavings in the chute/ action.

  The MDR scissor ejector pushes the case off the bolt face into the paw in the ejection chute, then the case is pushed out as the bolt moves forward.  This is the first snag in the ejection cycle as the case comes into contact with the sharp edge of the paw.  This contact often causes case damage as the sharp edge of the paw gouges the case.  I have tons of brass with deep cuts down the case wall, and through the rim from contact with the paw.

  As the bolt moves forward the case rim catches on the shoulder of the paw due to the sharp right angle.  The paw again being hardened steel wins the fight, leaving shavings of brass in the chute.  Here is a before shot of the chute with roughly 100 rounds through it.  This really isn't too bad.  I've opened it after long strings and brass shavings fall out.  You can clearly see the areas where contact is greatest and the brass is deposited.

(https://s19.postimg.cc/m9je3c7ib/KIMG0731.jpg) (https://postimg.cc/image/46qbc4bnj/)

  Now we come to the third snag in the system, the machined edge of the chute itself.  You may, or may not have this on yours. Looks to be a manufacturing problem. Not sure if its a byproduct of the MIM method, or just poor machining.   It's hard to see in the photo but the edge has a very rough finish and a bur.  Again this bur is hardened and nitrided.  As I pushed a case through the chute by hand I could feel the ridge cutting and scraping the case as it went.

(https://s19.postimg.cc/uf1g1iyc3/KIMG0739.jpg) (https://postimg.cc/image/x94lez0i7/)

  If you intend to reload cases fired from an MDR this case damage can be annoying, and the damage to the rims can be bad.  The only failure to eject out the chute I have had with my MDR was a case with one of these cuts in the rim getting caught on the chute.

 Reloading aside each of these three snags represent increased drag on the system, and that lost energy translates to reliability issues. Energy spent ripping up cases trying to push them over, or spit them out is energy not spent cycling the action.

  So I set out to remedy the problem.  It really wasn't that hard, but did require come careful hands. Given some simple tools, some mechanical know how and some careful fingers it can be done.

  Here's basically what I used.  Whatever abrasives you like, but the razor and needle nose pliers are a must.

(https://s19.postimg.cc/v4k8dzm1v/KIMG0744.jpg) (https://postimg.cc/image/4jhpifjof/)

I also used a 400 grit flap wheel and buffing wheel with Tripoli compound, but that's kinda overkill.

Okay, so how do we get this thing out?  Well here's how it goes in. 1:48 https://youtu.be/xgwj3OG3Nag (https://youtu.be/xgwj3OG3Nag)

There are two tinydetents and a spring in a shaft that runs lengthwise across the paw.  When pushed in from the outside of the chute they pop out and hold the paw in place.  The bottom of the paw has a channel for the leaf style spring to lock in.  Here's what it looks like apart.

(https://s19.postimg.cc/5lrw0uzw3/KIMG0735.jpg) (https://postimg.cc/image/cc8daan1r/)

  Okay so the tricky part is the detents, and not losing them. :D  I started with a dental pick but found the razor to be the right tool for the job.  Carefully place the point between the tip of the detent, and gently push it in until the detent retracts back into the paw.  I found you can pop out one side at a time, but be careful not to lose the detent. Place your hand over the back of the paw and if the detent is retracted enough you should be able to push the paw back through the chute.  Working in a clean area or placing it in a box will help keep track of the parts if they pop out. 

 Once apart everything is real easy to clean up to your liking.  I chose to use a 120 grit drum on the Dremel to knock off the sharp edges and the corner of the paw.  I then took 220 and 400 grit to clean up the work.  Finished it up with a spin on the 400 grit flap wheel and buffing wheel. 
 
  To remove the jagged edge on the chute I wrapped some 400 grit around a pencil and ran it over the edge.  I put some buffing compound on the Dremel buffing wheel (Harbor freight ;D) and went to town on the whole chute.

 After I was happy with the abrasive work I degreased the parts, and hit everything with Flitz. Man that stuff is great.

 Here's how it turned out.  The focus on the first is a little weird, the paw is shiny now.

(https://s19.postimg.cc/bzgz48f3n/KIMG0742.jpg) (https://postimg.cc/image/szzvcws4v/)

(https://s19.postimg.cc/f6binrzir/KIMG0745.jpg) (https://postimg.cc/image/9i57wvv67/)

  Going back together isn't to hard. I found the needle nose pliers helpful for holding the detent and pushing it back into the shaft over the spring. Large side of the detent goes in, small tip, out.  Just do the inverse of taking it out, one side at a time. Carefully.

  The difference is really incredible.  I would say it takes about 30% less force to get a case into the chute with the new finish.  I didn't mess with the overall size of the paw so it still holds the case securely.  Going forward over the paw, and out the chute is smooth as glass.

  Haven't shot it yet but I think case damage will be nonexistent, and it should run much smoother. I'll update when I have some fired cases.


Title: Re: .308 MDR Ejection chute (fixed)
Post by: GoShort on June 13, 2018, 07:40:20 AM
Awesome post
Thanks a bunch
I have been making a list of things to check / do and detailed fixes like this are great
Excited for when my MDR arrives.

Sent from my Nexus 5X using Tapatalk



Title: Re: .308 MDR Ejection chute (fixed)
Post by: AF Gunner on June 13, 2018, 08:25:56 AM
Awesome write up, I will be doing this to mine. I stoned the edges of the paw while still installed in the cover. I knew it would be better if I could get the Paw out, just hadn't tried to figure out how to remove. Now I know... Thanks!.

Gunner.


Title: Re: .308 MDR Ejection chute (fixed)
Post by: thehun on June 13, 2018, 08:48:27 AM
Flitz to the rescue...that stuff has lots of great uses.


Title: Re: .308 MDR Ejection chute (fixed)
Post by: coldboremiracle on June 13, 2018, 09:27:03 AM
Standby for reports of lost chute clip retainers and spring. ;)


Title: Re: .308 MDR Ejection chute (fixed)
Post by: CabbitOne on June 13, 2018, 12:51:03 PM
And when will you start offering this service? And how much?  :P

Makes me wonder about having it stripped, polished, and re-finished with one of these super low friction finishes....

Also nice work, pictures make it look fantastic.

Standby for reports of lost chute clip retainers and spring. ;)

^ This too. Hope y'all have spares for sale!


Title: Re: .308 MDR Ejection chute (fixed)
Post by: Box on June 13, 2018, 01:08:37 PM
I hope DT is taking notes.


Title: Re: .308 MDR Ejection chute (fixed)
Post by: reason on June 13, 2018, 01:40:30 PM
It will be interesting to see how someone who has a fresh MDR that only has maybe 50 rounds into the break in process, who then does this, to see what difference it makes in feeding and functioning.


Title: Re: .308 MDR Ejection chute (fixed)
Post by: Aussie E on June 13, 2018, 06:44:27 PM
Do all these "fixes" effect the warranty?

AE


Title: Re: .308 MDR Ejection chute (fixed)
Post by: GoShort on June 13, 2018, 06:56:39 PM
You could remove the recoil spring. Then load a spent cartridge into the chamber, pull back and lock the bolt back the use a trigger pull guage to pull it forward to manually cycle it to see how much force it takes. Would need a loaded mag in there also.

Would be ideal to do this on an fresh out the box rifle, then after 200+ rnds, and one last time after smoothing the ejection parts. So you can compare all 3 numbers.

Sent from my Nexus 5X using Tapatalk



Title: Re: .308 MDR Ejection chute (fixed)
Post by: HBeretta on June 13, 2018, 07:46:32 PM
great post.  i'm curious how your rifle performs now.


Title: Re: .308 MDR Ejection chute (fixed)
Post by: jreffner on June 13, 2018, 09:49:02 PM
I think that Desert Tech should:

1. Start making these modifications on all rifles that haven't left their factory yet.

2. Offer to fix all the ones they have sent out free of charge.

3. Give BlackandWhiteKnight a refund, and a job offer for all of his hard work.

Seriously though, I'm not screwing with all of this.  I have a .223 on order and nothing would make me happier than DT publicly announcing that all will be fixed.  I really don't want to cancel my order, but as I said, I am not going through all of this for the money that has been spent.  So DT, what is the plan?  Are you going to keep sending them out as is, or admit there are problems, and then fix them (especially now that you know what the problems are)?  Hint:  The correct answer is the latter.  Another delay is far better than trashing your reputation.  Please fix this!


Title: Re: .308 MDR Ejection chute (fixed)
Post by: mityno1 on June 13, 2018, 11:23:21 PM
I think that Desert Tech should:

1. Start making these modifications on all rifles that haven't left their factory yet.

2. Offer to fix all the ones they have sent out free of charge.

3. Give BlackandWhiteKnight a refund, and a job offer for all of his hard work.

Seriously though, I'm not screwing with all of this.  I have a .223 on order and nothing would make me happier than DT publicly announcing that all will be fixed.  I really don't want to cancel my order, but as I said, I am not going through all of this for the money that has been spent.  So DT, what is the plan?  Are you going to keep sending them out as is, or admit there are problems, and then fix them (especially now that you know what the problems are)?  Hint:  The correct answer is the latter.  Another delay is far better than trashing your reputation.  Please fix this!

Without serial numbers, we don't know where in the production sequence the MDR's with reported issues were made. For all we know, these are issues limited to a certain, perhaps early batch of MDR's and current production MDR's have already had these issues addressed.

5.56 is half the power of .308 with projectiles 1/3 the weight of .308. It is unlikely the 5.56 version will have the exact same problems as have been reported for the .308's. 


Title: Re: .308 MDR Ejection chute (fixed)
Post by: ney1 on June 14, 2018, 12:14:56 AM
Blackandwhiteknight,
Did you actually have reliability issues with your MDR prior to dehorning the edges of the ejection chute?  In reading your post I interpret that you did not but rather you were trying to avoid scrapes on your ejecting brass?  

Scratches on ejecting brass out of a semi-automatic rifle is does not mean the rifle is broken and needs to be fixed.  The MDR is not a precision sniper rifle it is a field rifle with a lot of innovative features in it.

I do like how you dehorned the edges though and appreciate you sharing your modification.

Thanks

Nick


Title: Re: .308 MDR Ejection chute (fixed)
Post by: jreffner on June 14, 2018, 08:48:10 AM

Without serial numbers, we don't know where in the production sequence the MDR's with reported issues were made. For all we know, these are issues limited to a certain, perhaps early batch of MDR's and current production MDR's have already had these issues addressed.

5.56 is half the power of .308 with projectiles 1/3 the weight of .308. It is unlikely the 5.56 version will have the exact same problems as have been reported for the .308's. 
[/quote]

Thank you for this info!


Title: Re: .308 MDR Ejection chute (fixed)
Post by: newguy2k3 on June 14, 2018, 09:29:58 AM
Blackandwhiteknight,
Did you actually have reliability issues with your MDR prior to dehorning the edges of the ejection chute?  In reading your post I interpret that you did not but rather you were trying to avoid scrapes on your ejecting brass?  

Scratches on ejecting brass out of a semi-automatic rifle is does not mean the rifle is broken and needs to be fixed.  The MDR is not a precision sniper rifle it is a field rifle with a lot of innovative features in it.

I do like how you dehorned the edges though and appreciate you sharing your modification.

Thanks

Nick

For me and probably others it's a reliability mod with the added benefit that brass gets gouged less. Before smoothing the lip rarely could I ever eject a round by hand and not have it jam halfway into the ejection chute no matter how hard I tried to cycle it.


Title: Re: .308 MDR Ejection chute (fixed)
Post by: GoShort on June 14, 2018, 10:48:28 AM
My thought would be when does DT receive these parts pre or post coating. If pre they could easily add a step to sand the paw and ejection chute edges before sending to coating. If post they would need to sand then recoat. Which would cost more and present more issues.
I doubt they would want to sand them post coating and send them out as it would expose bare metal to wear and corrosion.

I am sure they could request it pre as they did with the chamber for the mentioned coating issue.

Sent from my Nexus 5X using Tapatalk



Title: Re: .308 MDR Ejection chute (fixed)
Post by: ney1 on June 18, 2018, 01:12:28 PM
Thanks for sharing this with everyone!