Results 1 to 10 of 45
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11-04-2017, 12:48 #1
- Join Date
- Dec 2013
- Age
- 54
- Posts
- 11
PMP brass not extracting from DM4
Hi folks. I'm having an issue with my DM4 (.223) not extracting factory PMP brass reliably. I'm using an 18inch semi weight barrel, manufactured by Musgrave, that comes standard with the rifle. The rifle shoots everything else I've tested, with no issues at all, (including my own reloads) except factory PMP .223 Remington, (the brown box). The spent cases stay stuck in the chamber even after the bolt has cycled backwards. This occurs once about every 3-4 rounds. The case extracts like normal, once I've allowed the bolt to shut close again, so it's not sitting unusually tight. I've had the smiths at Diplopoint check it out for me, but there was nothing to fix or replace, because it only has this issue with PMP ammo. Has any other DM4 owner out there experienced similar issues with PMP ammo? I'd really appreciate your input if you've come up with a fix. One fellow shooter suggested that the pressure in the chamber, might still be peaking, while the BCG is cycling rearwards and therefore would not extract the case. Any thought on this?
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11-04-2017, 13:10 #2
- Join Date
- May 2009
- Location
- Johannesburg
- Posts
- 6,444
Re: PMP brass not extracting from DM4
I'm no gunsmith, but my money is on a faulty extractor. Try and get yours changed out.
To add, how many rounds through your rifle right now? What other types of ammo have you been using?
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11-04-2017, 13:10 #3
- Join Date
- Mar 2016
- Location
- Klein Karoo
- Age
- 56
- Posts
- 1,024
Re: PMP brass not extracting from DM4
Not having much experience with the 5.56/.223 difference, but having read about it, I have a question.
I would assume the rifle is chambered for 5.56 Nato, and from what I've read .223 Rem in a 5.56 Nato chamber develops significantly less pressure than the military ammo. With which other ammo have you tried?
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11-04-2017, 13:20 #4
- Join Date
- Dec 2010
- Location
- Boland
- Posts
- 7,985
Re: PMP brass not extracting from DM4
Have you done your own reloads using the cases that give problems? How do they function?
When the gun is in battery the extractor must already be slipped over the rim. Barring stuck case issues (which you seem to indicate is not the problem) the case MUST extract as the bolt moves rearwards. Thus, the extractor is slipping back over the rim. Either the cases are faulty (i.e. incorrectly shaped at the rim) the extractor spring tension is insufficient or the extractor shape is incorrect.
Pressure really shouldn't still be peaking by the time the BCG moves backwards, I'm sure you'd notice that in the recoil, and the BCG beating itself to death...
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11-04-2017, 13:21 #5
- Join Date
- Oct 2013
- Location
- Johannesburg
- Age
- 32
- Posts
- 1,711
Re: PMP brass not extracting from DM4
My DM4 "14.5" has not had any problems with PMP yet, i have however had a few problems with barnaul nickle platted cases. fail to Extract and got a stuck case after it ripped some of the rim off. Major issues with surplus M193 so i suspect the chambers are cut tight
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11-04-2017, 14:00 #6
- Join Date
- Aug 2013
- Location
- Pretoria
- Posts
- 2,475
Re: PMP brass not extracting from DM4
An inexpensive o-ring Think it was a 2.90 x 1.78 Viton with an 80 durometer should add additional tension: Not a DM4 but still an AR:
http://www.gunsite.co.za/forums/show...ilure-to-Eject
I have only used PMP ammo in my CQA so far, and after adding the O-ring haven't had any issues extracting
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11-04-2017, 16:14 #7
- Join Date
- Oct 2010
- Location
- /\/¯¯¯¯¯\/\
- Age
- 43
- Posts
- 10,754
Re: PMP brass not extracting from DM4
is the chamber milspec? polish / ream the chamber?
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11-04-2017, 18:12 #8
- Join Date
- Aug 2008
- Posts
- 1,308
Re: PMP brass not extracting from DM4
You don't state that there is a 2nd round being fed from the magazine that is jammed against the fired case in the chamber, the presence of this would be a good indicator of the next steps.
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11-04-2017, 20:30 #9
- Join Date
- Jan 2016
- Location
- ZA
- Posts
- 118
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11-04-2017, 22:08 #10
- Join Date
- May 2009
- Location
- Johannesburg
- Posts
- 6,444
Re: PMP brass not extracting from DM4
Question: if it was a case of not enough gas to push the bolt all the way back, wouldn't it then be a case of reloads not extracting and factory ammo working? The PMP isn't milsurp hot but it's not soft either. In my limited experience it's had enough oomph to cycle properly.
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