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Link Posted: 1/22/2019 9:02:24 AM EDT
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Quoted:
So, in other words, this thing costs about $1,000 more than a Kel-Tec RFB, has far more malfunctions, quality control issues, a 3-year warranty vs. a lifetime warranty and customer service that recommends you take a nail file (hmm, never heard of an armorers kit including a nail file before ) to burrs compared to glowing reports of how “Kel-Tec will make it right” customer service philosophy.  Seen an MDR in the local fun store several months ago.  Damn glad I never bit on that one and will be saving my pennies for an RFB instead.
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Pretty much
Link Posted: 1/22/2019 9:56:29 AM EDT
I'm going to do a little more checking tonight.  Maybe cast the chamber if I can find my bar of cerrosafe.  Then I think I'm going to ream it if it's as tight as I think.  My .308 reamer has chambered both bolt guns and AR10s and they've all had plenty of throat.  Maybe first I'll see if it closes up on my go gage.  I expect it does.
Link Posted: 1/22/2019 11:00:53 AM EDT
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Quoted:
I'm going to do a little more checking tonight.  Maybe cast the chamber if I can find my bar of cerrosafe.  Then I think I'm going to ream it if it's as tight as I think.  My .308 reamer has chambered both bolt guns and AR10s and they've all had plenty of throat.  Maybe first I'll see if it closes up on my go gage.  I expect it does.
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If DT seriously reamed the chambers to match grade bolt-gun specs... I'm going to mock them endlessly. That would be as big an oversight as using annealed alloy for locking parts.
Link Posted: 1/22/2019 8:41:04 PM EDT
My go gage passes but that doesn't surprise me. They really only check distance relative to form of the shoulder to the bolt face.

I think there's a problem in front of the shoulder.

I can mark up any number of loaded rounds of whatever I have on hand and after chambering they look like this.

Attachment Attached File
Link Posted: 1/22/2019 8:58:47 PM EDT
So even though I haven't slugged it, I stuck my reamer in there. First, that's a non starter. The chamber is silver in color but must be melonited or something because I couldn't scratch it.

And what that allowed me to do was push on it a bit without worrying about cutting anything. As opposed to a go gage, a chamber reamer can "check" form on all geometry.

Holy fuck was it tight. Not my bushing guide in the bore, I checked. But as soon as the shoulder made contact I almost couldn't turn it. It just locked right up.

I think what's happening is that a nominally sized case hits where my witness marks are and essentially sizes the front of the shoulder a bit.  Then under pressure of firing this ring lock for lack of a better term causes greater than normal neck length growth, to the point of swaging the neck into the throat of the bore and greatly increasing friction opposing extraction.

But that's just a guess. It's a tighter chamber than I've ever seen on a 7.62 gas gun to the best I can tell without slugging it.  I'll order a new bar of cerrosafe and do so before going crazy with a lap or something. It would be nice to have all the dimensions of the chamber.
Link Posted: 1/22/2019 11:10:17 PM EDT
I think they're nitrided.

I don't have any go/nogo gauges but I do have the Hornady headspace comparator tool. 308 out of the box usually measures 1.620". Fired brass from my 308 SRS barrel and noveske 21" 308 are right at 1.622". 16" CL Mws barrel comes out at 1.625 and MDR fired brass is 1.626. I want to say the RFB I had came in somewhere between 1.625-30.

Neck dimensions on fired brass compares to the other barrels. .313-4 id and .345 od.
Link Posted: 1/23/2019 12:15:26 AM EDT
I've always suspected that the MDR's chamber is off...
Link Posted: 1/23/2019 11:08:11 AM EDT
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Just popped the last cartridge that I ripped the rim off. German DAG (that has run 100% in a number of FALs including a century, as well as a SCAR and MWS) and noticed these brass marks.

My chamber was quite clean.  I thought maybe it was the necks sticking but this says otherwise.

https://www.AR15.Com/media/mediaFiles/125898/20190121_202921_jpg-817046.JPGhttps://www.AR15.Com/media/mediaFiles/125898/Screenshot_20190121-203024_Gallery_jpg-817048.JPGhttps://www.AR15.Com/media/mediaFiles/125898/SmartSelect_20190121-203049_Gallery_jpg-817051.JPG

They go all the way around the case.

They also exist at the base, but mostly where the cartridge protrudes from the chamber.

I'll get my borescope  out and see if I can find anything in there causing this.
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I wonder if a lot less gas and a fluted chamber would fix the damn thing.
Link Posted: 1/23/2019 11:25:37 AM EDT
Ordered the Cerrosafe.  When it comes we'll be able to see exactly what the chamber is.
Link Posted: 1/23/2019 12:24:51 PM EDT
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Quoted:
Ordered the Cerrosafe.  When it comes we'll be able to see exactly what the chamber is.
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Link Posted: 1/23/2019 2:25:21 PM EDT
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Quoted:

I wonder if a lot less gas and a fluted chamber would fix the damn thing.
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Less gas and then you don't always have enough inertia to fully cycle it.
Link Posted: 1/23/2019 2:37:31 PM EDT
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Quoted:
Less gas and then you don't always have enough inertia to fully cycle it.
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Fluted chamber means easier extraction, so maybe you wouldn't need as much gas to get full cycle, even without adding carrier weight.
Link Posted: 1/23/2019 2:53:01 PM EDT
Quite honestly...a proper, smooth chamber...does not need flutes...
Link Posted: 1/23/2019 2:55:21 PM EDT
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Quoted:
Fluted chamber means easier extraction, so maybe you wouldn't need as much gas to get full cycle, even without adding carrier weight.
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Quoted:
Quoted:
Less gas and then you don't always have enough inertia to fully cycle it.
Fluted chamber means easier extraction, so maybe you wouldn't need as much gas to get full cycle, even without adding carrier weight.
Yep, see the HK G3/91/MP5/P7 etc and POF's E2Extraction:
https://pof-usa.com/e2-extraction-infoulable-extraction-technology
Link Posted: 1/23/2019 3:00:39 PM EDT
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Quoted:

Fluted chamber means easier extraction, so maybe you wouldn't need as much gas to get full cycle, even without adding carrier weight.
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this.

them rims getting yanked off because there still too much pressure during extraction.

fluting will allow them to get yanked out easier.

but its gonna get gassy and dirty in there.
Link Posted: 1/23/2019 3:17:40 PM EDT
It's already pretty dirty.  In the little bit I've shot mine suppressed it fouls the magazine and subsequent rounds far more than my AR10 ever did.
Link Posted: 1/23/2019 3:52:18 PM EDT
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Quoted:

this.

them rims getting yanked off because there still too much pressure during extraction.

fluting will allow them to get yanked out easier.

but its gonna get gassy and dirty in there.
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Dirtiness...which the MDR cannot handle...you get it slightly dirty and the system chokes...
Link Posted: 1/23/2019 5:00:47 PM EDT
I checked my MDR fired brass, same equatorial? marks around the fired brass; sharpie'd up shoulder shows the same marks as Kuraki's; measured my fired brass, shorter cases had no damage, longer cases (Hirtenberger) had ripped rims, just like Rabbit-Slayer.

My BCG has 0 play in it on the rails compared to newguy2k3's post.
Link Posted: 1/23/2019 5:20:17 PM EDT
MDR 5.56 at SHOT Range Day: https://youtu.be/FLjUtF6cwHc?t=170

Note the lack of an ejection chute...guess they haven't finished re designing them by January as they said they would...
Link Posted: 1/23/2019 5:30:25 PM EDT
Well to their defense they projected it out to early February...however one would think that the so-called "vendor" would have provided final production models for DT to approve and test...and such chutes would have made it to Shot Show.

But...in typical DT fashion...the customers will ultimately test the chutes...
Link Posted: 1/23/2019 6:30:27 PM EDT
I'd rather fix the root problem which I believe is the extraction timing. Delay extraction and the case won't be so stuck in the chamber and there should be less pressure remaining in the bore to foul the action. I'd rather have a longer gas system but not having a mill and lathe it's more than I want to undertake having to pay someone else to make the parts. Adding reciprocating mass with lathe time for a heavier guide rod I'm willing to chance. I the more I think about it maybe it does need more weight. It not only has to travel fully rearward every time, partway through the travel it has to start movement of the scissor mechanism, which has considerable mass to it, and still keep going.

ETA: contacted DT about the sloppy bolt carrier fit and the bolt and barrel damage it is causing and if that was acceptable or out of spec. Warranty is supposedly waiting on a reply from engineering. I guess I'm expecting too much to think that the department that is suppose to be in charge of fixing these rifles would have info like that easily available and understand how these rifles(are supposed to) work.

Eta2: I thought the main advantage to piston operating systems is that the action is supposed to stay cleaner? It really is the dirtiest semi auto firearm I've ever seen.
Link Posted: 1/23/2019 9:00:41 PM EDT
Well. Properly designed one yes. A DT designed one...no.
Link Posted: 1/23/2019 9:06:32 PM EDT
The amount of gas being dumped out of the bore is just another bit of evidence that the timing of extraction is wonky.

A short stroke piston should be one of, if not the cleanest method of operation an auto can have.
Link Posted: 1/23/2019 9:15:47 PM EDT
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Quoted:
I'd rather fix the root problem which I believe is the extraction timing. Delay extraction and the case won't be so stuck in the chamber and there should be less pressure remaining in the bore to foul the action. I'd rather have a longer gas system but not having a mill and lathe it's more than I want to undertake having to pay someone else to make the parts. Adding reciprocating mass with lathe time for a heavier guide rod I'm willing to chance. I the more I think about it maybe it does need more weight. It not only has to travel fully rearward every time, partway through the travel it has to start movement of the scissor mechanism, which has considerable mass to it, and still keep going.

ETA: contacted DT about the sloppy bolt carrier fit and the bolt and barrel damage it is causing and if that was acceptable or out of spec. Warranty is supposedly waiting on a reply from engineering. I guess I'm expecting too much to think that the department that is suppose to be in charge of fixing these rifles would have info like that easily available and understand how these rifles(are supposed to) work.

Eta2: I thought the main advantage to piston operating systems is that the action is supposed to stay cleaner? It really is the dirtiest semi auto firearm I've ever seen.
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That what I thought too, so I built a Piston AR...

Just as dirty suppressed.  After 3 mags in my OD AUG its black inside.  What really drove it home for me was when I removed the bolt from my .223AI bolt rifle (with a suppressor) and couldn't see through the bore.  Baffled cans hold gas in the barrel period.  That's why my last 3 suppressors were/are OSS and a Tranquillo.  Muzzle reflections be damned I can see and breath....
Link Posted: 1/23/2019 9:16:57 PM EDT
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The amount of gas being dumped out of the bore is just another bit of evidence that the timing of extraction is wonky.

A short stroke piston should be one of, if not the cleanest method of operation an auto can have.
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Don't shoot an AUG suppressed with a shirt you want to keep...
Link Posted: 1/23/2019 9:17:07 PM EDT
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Quoted:I thought the main advantage to piston operating systems is that the action is supposed to stay cleaner? It really is the dirtiest semi auto firearm I've ever seen.
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DI master race FTW!
Link Posted: 1/23/2019 9:48:39 PM EDT
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Quoted:
Eta2: I thought the main advantage to piston operating systems is that the action is supposed to stay cleaner? It really is the dirtiest semi auto firearm I've ever seen.
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OOooh, now that sounds like a challenge!  My MPX is "that gun" for me - I love my many other piston guns, AR-pattern and others, but that #^%$% MPX is dirtier than even my straight-blowback 9mms...  Roller-locked master race I guess

So yes, a properly designed piston gun does run cleaner, and I'd venture to say that's true suppressed or unsuppressed - suppressed is obviously dirtier than un-, but comparing the same suppressor across two guns, or two guns both unsuppressed I think piston still comes out cleaner.
Link Posted: 1/24/2019 9:25:02 AM EDT
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DI master race FTW!
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Don't mention DI guns...they are inferior...remember...the LMT MWS is no where near DT MDR levels of excellence per DT...don't you remember?
Link Posted: 1/26/2019 2:04:08 AM EDT
It seems SHOT is not without irony; Desert Tech was placed next to Kel Tec, making for many direct comparisons.  At least IndoMIM was not immediately nearby.
Link Posted: 1/26/2019 9:32:53 AM EDT
The Keltec booth was 4 times the size of DT and had a lot more traffic. Helps to have pistol, rifles and shotguns.
Link Posted: 1/26/2019 11:57:41 AM EDT
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Quoted:
The Keltec booth was 4 times the size of DT and had a lot more traffic. Helps to have pistol, rifles and shotguns - which all actually work.
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FIFY
Link Posted: 1/26/2019 1:32:24 PM EDT
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Quoted:
The Keltec booth was 4 times the size of DT and had a lot more traffic. Helps to have pistol, rifles and shotguns.
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Sadly, DT's move also meant there was nearly nothing of interest in the LEO Ballroom area.  Rather uninspiring show this year, on the whole.
Link Posted: 1/26/2019 2:11:52 PM EDT
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Quoted:
Sadly, DT's move also meant there was nearly nothing of interest in the LEO Ballroom area.  Rather uninspiring show this year, on the whole.
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Quoted:
Quoted:
The Keltec booth was 4 times the size of DT and had a lot more traffic. Helps to have pistol, rifles and shotguns.
Sadly, DT's move also meant there was nearly nothing of interest in the LEO Ballroom area.  Rather uninspiring show this year, on the whole.
Only booth I was interested in in the LEO Ballroom was LMT.
Link Posted: 1/26/2019 9:04:28 PM EDT
Link Posted: 1/26/2019 9:20:41 PM EDT
Compared to a loaded cartridge that gages perfectly in my case gage.

Attachment Attached File
Link Posted: 1/26/2019 9:26:00 PM EDT
Neck diameter and length seems fine. The only thing I can see that cause interference are the areas that show up on the magic marker cases. The case shoulder is rounded where the chamber is sharp (red and blue)  and the length of that is as near as I can measure very close to size on size. (Yellow to blue/red)

I wish I had an optical comparator.

Attachment Attached File
Link Posted: 1/26/2019 9:27:42 PM EDT
Last point, the chamber slug very nearly fits the case gage, but not quite. It shouldn't obviously.
Link Posted: 1/26/2019 9:33:35 PM EDT
Link Posted: 1/26/2019 9:36:13 PM EDT
So that .140" length is a problem since max case dimension is .152" and the .343" neck is size on size with max case neck diameter.
Link Posted: 1/26/2019 9:37:42 PM EDT
The shoulder diameter at .452" is less than max case as well.

The thing is tight.
Link Posted: 1/27/2019 1:42:27 AM EDT
How does the chamber casting compare to your fired case?

Jesse
Link Posted: 1/27/2019 2:59:01 AM EDT
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Quoted:
How does the chamber casting compare to your fired case?

Jesse
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I can't lay hands on my torn rim example at the moment but my 2.005 oal cases that extracted fine are essentially fire formed to the same dimensions, including the sharp corner at the shoulder.
Link Posted: 1/27/2019 10:01:39 AM EDT
Well...look it there...now take a DT match ammo...and take its dimensions...I bet its the same
Link Posted: 1/27/2019 10:01:48 AM EDT
Good lord, that chamber is bolt-action tight. I can't believe they did that... I wonder if it was intentional, not for accuracy concerns or out of habit ("all our rifles are chambered to this spec!"), but to further delay the massively early extraction.
Link Posted: 1/27/2019 10:53:41 AM EDT
The barrels are from Faxon right? Given how much DT has outsourced parts for this thing I wonder did they chamber them in house? If someone else did surely they would have suggested a bit more forgiving chamber.
Link Posted: 1/27/2019 5:07:57 PM EDT
Yes. Faxon makes the barrels.

I don’t think DT produces much on this rifle at all. Hence why the quality of the weapon is so whacky.
Link Posted: 1/27/2019 5:34:46 PM EDT
Damn dude you fucked up your thumbnail.
Link Posted: 1/27/2019 7:53:35 PM EDT
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Quoted:
Damn dude you fucked up your thumbnail.
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Lol
Link Posted: 1/27/2019 8:25:55 PM EDT
Doesn't look bad. It's not completely purple and it's still attached.
Link Posted: 1/27/2019 9:09:10 PM EDT
Dog bit right through it when I was wrasslin with him and his chew toy.  Complete freak accident, got my thumb on top of the toy way back under a molar as he was chomping down

That fucker hurt for a spell.
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