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| |-+  Desert Tech MDR (Moderator: Heathsrow)
| | |-+  Redesign the MDR
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Author Topic: Redesign the MDR  (Read 9589 times)
newguy2k3
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« Reply #180 on: February 08, 2019, 07:53:57 AM »

Tungsten alloy spring guide/op rod came out at 8.8oz vs the factory 4oz made to the same dimensions.
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thehun
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« Reply #181 on: February 08, 2019, 12:51:58 PM »

Nice...pics?
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newguy2k3
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« Reply #182 on: February 09, 2019, 08:52:52 PM »

 So a bit of seemingly good news.

I stepped out behind the house before dark and fired off about 10rounds of my normal 175smk load with the sps300 suppressor. I've had to run this on setting 2. On setting one, loading one round it would lock back on an empty mag but never eject with a full mag.

Fired one round on setting 2 to check that it locked back and everything felt right. Loaded a few rounds and it went through those fine. Changed to setting one for the last 4-5 mag fed. One short stroked just a bit but the rest functioned fine. I was also shooting at about a 25-30 degree downward angle so that didn't help.

So the takeaway here? Seemingly. Setting one at 13.5oz of reciprocating mass doesn't give enough inertia to reliably cycle the ejection mechanism. Even though the BCG is almost certainly travelling slower with the extra 4.8oz it has more inertia.

Obviously I'm going to have to test more and I want to compare felt recoil between the two back to back but there is a glimmer of hope at least.
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spector762
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« Reply #183 on: February 09, 2019, 09:06:04 PM »

So a bit of seemingly good news.

I stepped out behind the house before dark and fired off about 10rounds of my normal 175smk load with the sps300 suppressor. I've had to run this on setting 2. On setting one, loading one round it would lock back on an empty mag but never eject with a full mag.

Fired one round on setting 2 to check that it locked back and everything felt right. Loaded a few rounds and it went through those fine. Changed to setting one for the last 4-5 mag fed. One short stroked just a bit but the rest functioned fine. I was also shooting at about a 25-30 degree downward angle so that didn't help.

So the takeaway here? Seemingly. Setting one at 13.5oz of reciprocating mass doesn't give enough inertia to reliably cycle the ejection mechanism. Even though the BCG is almost certainly travelling slower with the extra 4.8oz it has more inertia.

Obviously I'm going to have to test more and I want to compare felt recoil between the two back to back but there is a glimmer of hope at least.
  so its a step in the right direction now i am curious to see a plug in there with more volume and a tad larger port hole 
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newguy2k3
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« Reply #184 on: February 10, 2019, 11:43:47 PM »

Fired about another 20 rounds this afternoon when I had a minute. The suppressor, ammo and gas setting combo that gave me a stuck case a few weeks ago ran perfectly fine and had no rim damage to be seen.

On setting one the combination that short stroked before still does but about half as frequently.

I'm fairly confident in saying the felt recoil is no worse. Possibly a little softer impulse than before. Still much sharper than a shatty DI ar pattern rifle.

Obviously it's not definitive but things are still looking up. I want to shoot the stock vs heavier rod back to back to compare recoil and do a more thorough test of ammo, gas setting vs function.
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whiskey91lima
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« Reply #185 on: February 10, 2019, 11:46:43 PM »

What about reducing the recoil spring tension?

Even though it's short stroking, it is still heavily gassed. DT probably made up for this by using a heavy spring.
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newguy2k3
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« Reply #186 on: February 10, 2019, 11:51:13 PM »

I was having failure to return to battery issues before and replacing the spring seemed to fix that. I'm not wanting to try to go down that road at the moment.

I may look into finding some other springs to try out of curiosity though. I need to measure it.
« Last Edit: February 10, 2019, 11:53:00 PM by newguy2k3 » Logged
JesseJames38
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« Reply #187 on: February 11, 2019, 02:08:51 AM »

If you don't mind me asking, about how much did the new tungsten guide rod cost.  I am also wondering how the durability of this new guide rod will be.   Be interested in hearing about the reliability of this along with how it holds up.

thanks
Jesse.
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newguy2k3
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« Reply #188 on: February 11, 2019, 06:27:34 AM »

If you don't mind me asking, about how much did the new tungsten guide rod cost.  I am also wondering how the durability of this new guide rod will be.   Be interested in hearing about the reliability of this along with how it holds up.

thanks
Jesse.

It was a $125 piece of tungsten alloy stock and the machining was considerably more being a one off job. They did an excellent job though. I wish I had told them to bump the diameter .020". Would have given an extra oz.

After a year and a half and 3 trips to DT I'm sick of having a gun that's not reliable.
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thehun
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« Reply #189 on: February 11, 2019, 09:57:46 AM »

Hats off to you sir for undertaking something and proving the concepts we have been talking about....hope DT takes note...and improve the system overall...
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EWTHeckman
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« Reply #190 on: February 11, 2019, 11:33:55 AM »

Hats off to you sir for undertaking something and proving the concepts we have been talking about....hope DT takes note...and improve the system overall...

I second the motion. All in favor?
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spector762
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« Reply #191 on: February 11, 2019, 11:41:17 AM »

If you don't mind me asking, about how much did the new tungsten guide rod cost.  I am also wondering how the durability of this new guide rod will be.   Be interested in hearing about the reliability of this along with how it holds up.
W
thanks
Jesse.

It was a $125 piece of tungsten alloy stock and the machining was considerably more being a one off job. They did an excellent job though. I wish I had told them to bump the diameter .020". Would have given an extra oz.

After a year and a half and 3 trips to DT I'm sick of having a gun that's not reliable.
I ordered the tungsten this morning I am going to see if I can over size it a tad more and hopefully with the plug I am making i can duplicate and mabey fine tune it
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thehun
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« Reply #192 on: February 11, 2019, 11:55:33 AM »

What are the thoughts on the brittleness of tungsten?
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newguy2k3
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« Reply #193 on: February 11, 2019, 12:21:52 PM »

It's a gamble. It's a tungsten, nickel, copper alloy so not pure which should help. I have a feeling that if it's going to fail it will be right where it's turned down and threads into the bolt carrier. All the stress on it is linear though and it has a support that runs on rails at the opposite end from the bolt carrier.

We'll see.
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thehun
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« Reply #194 on: February 11, 2019, 12:44:18 PM »

This sounds a bit silly but could you "add" weights to the carrier past the cam pin area as well as to the sides?

Maybe 3D print it and weld it on ... sounds uber redneck ... but the extra weight seems to help  Grin

Add a couple of more oz to the system that way....
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TNC
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« Reply #195 on: February 11, 2019, 12:51:30 PM »

What are the thoughts on the brittleness of tungsten?

Yeah, the brittleness in concert with its strength depends a lot on the quality of the tungsten as it pertains to its purity.  Not sure how they rate tungsten when you're ordering it know what level you get like compared to aluminum, steel, etc.  Obviously there has to be a rating, but I wouldn't know what it would represent...LOL!

Not having seen the schematic of an MDR, let me ask, does the guide spring rod(s) move or is it stationary?  My RFB has two guide rods for a pair of very long recoil springs with an additional short spring.  This apparently helps with recoil since most bullpups lack AR-like buffer systems.
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newguy2k3
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« Reply #196 on: February 11, 2019, 12:59:56 PM »

The guide rod is threaded into and moves with the carrier. It is also what the gas piston acts on to cycle the action.

Mt-17c is the alloy I used.
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newguy2k3
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« Reply #197 on: February 11, 2019, 01:24:18 PM »

BCG, barrel, etc torn apart


* EFB9A510-3827-433D-911A-242C3AEFE886.png (4297.08 KB, 2048x1536 - viewed 110 times.)
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NothisisPatrick
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« Reply #198 on: February 12, 2019, 07:32:05 PM »

Really cool you got that done, have you been able to do much more testing after the install?
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spector762
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« Reply #199 on: February 12, 2019, 07:39:47 PM »

got the experimental plug machined out and tapped


* 51868971_1717703991662600_2124869227847352320_n.jpg (537.16 KB, 1936x2592 - viewed 83 times.)
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