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Old 11-14-2017, 11:27 PM   #1
OHVET
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Default RPD Build

A good friend of mine got me excited about a belt fed SMG so I couldn't sleep thinking he would have one and I wouldn't. He has helped me quite a few time in my builds with welding and bailing me out when I got over my head in a machining issue. Many of my builds would not have been possible without his input. I also want to thank Rocket87, my new friend from Colorado, who was kind enough to send me the Shotgun News build articles. Rocket87 made me promise to post my progress so I thought I better get to it. I tried to find out as much as possible on the build. Like many of these SMG builds, the issue to solve is the semi auto trigger group. With my DPM and again with the RPD there were only a couple suppliers of trigger groups and the specs were not available as far as trigger pull and LOP. What I found was that all the suppliers used basically the same design. As a design engineer for almost 30 years it was easy for me to make a prototype of the trigger group from the available pictures and videos. After doing that it was obvious that the load of the striker spring would be added to the load of the return spring for the bolt carrier, so there was an issue of balancing these spring and have enough force to strike the primer and still have enough left to strip a round and lock the bolt. Another issue was by using the RPD trigger, the length of pull was fixed and, for me, it was way too long and unacceptable. My first challenge was a new trigger design. So, with my good friend, over a few cups of coffee, we decided on this design. On mine, I decided to use a semi auto shotgun trigger group. Here is how it all started. I will provide more pics as the build goes on if there is any interest in the thread.
Attached Images
File Type: jpg dIHwHfD.jpg (57.9 KB, 97 views)
File Type: jpg cGPmWG3.jpg (48.7 KB, 90 views)
File Type: jpg cMy50D6.jpg (88.7 KB, 88 views)

Last edited by OHVET; 11-14-2017 at 11:30 PM. Reason: spelling
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Old 11-14-2017, 11:40 PM   #2
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OHVET, thank you for your service, and thank you for keeping history alive. That RPD will be awesome when complete, way to put those engineering skills to good use.
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Old 11-15-2017, 12:15 AM   #3
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Definitely interested in your hammer fired conversation. The two I built as striker fired I got to run but definitely way more finicky than ideal. You are correct about balancing the springs, that's the tough part and I've found the action must be very smooth to make it reliable under that style conversion
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Old 11-15-2017, 12:23 AM   #4
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Looks cool! But its not a smg. An smg is a pistol caliber weapon. This is a lmg
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Old 11-15-2017, 12:53 AM   #5
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looking forward to see how it goes.
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Old 11-15-2017, 10:45 AM   #6
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The next problem was to get past the carrier return rod. The original design allows the rod to move back into the stock. As the return spring is compressed the rod travels back and down. To get my new push rod the travel back I needed to open up the hole in the grip frame. The new push rod is the same length as the original so the spring rate is not changed. A hole is dripped in the rear of the new push rod and the original rod is trimmed to fit. I drilled the hole as deep as I could without breaking through even though breaking through would not have been a problem because the rod rests against the spring cap. I used a piece of 1/2" bar and machined .100 off both sides after drilling and forming the rod tip. The hammer opening was milled out and relieved for smooth movement. The hammer sear was ground off and relocated to allow it to nest deeper into the grip frame.
https://i.imgur.com/PzuipCg.jpghttps://i.imgur.com/p79cAa4.jpghttps://i.imgur.com/YT5NGOl.jpghttps://i.imgur.com/P8XVG5W.jpghttps://i.imgur.com/js98P8U.jpghttps://i.imgur.com/pM1IlOY.jpghttps://www.dropbox.com/personal?preview=DSCF2938.AVI
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Old 11-15-2017, 12:03 PM   #7
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You are a few steps ahead of me....
(nice welds...)
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Old 11-15-2017, 12:29 PM   #8
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Quote:
Originally Posted by cal50 View Post
You are a few steps ahead of me....
(nice welds...)
Yea, he's a cheese dick but he does do awesome welding and machining.
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Old 11-15-2017, 11:14 PM   #9
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Quote:
Originally Posted by OHVET View Post





Didn't feel like opening all the tabs haha. Don't know how to embed the video and I couldn't access it when I clicked on it since I don't have an account.

Hell of a job!
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Old 11-15-2017, 11:16 PM   #10
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You are about to get NAILED.
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Old 11-15-2017, 11:57 PM   #11
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Pretty much just another AK assembly from here. I don't know how to post a video either.

Last edited by OHVET; 11-15-2017 at 11:59 PM. Reason: added info
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Old 11-16-2017, 08:02 AM   #12
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Quote:
Originally Posted by raggedwhole! View Post
You are about to get NAILED.
Please do tell.
I am doing a build similar but using standard AR fire control parts.

All the approved BATFE mods are performed like cutting off the auto sear, cutting off the sear notch on the carrier, milling down the carrier to fit the DSARMS receiver, transfer pin in carrier, etc. so the prior approved design parts and operation is not changed.

The hammer system is the only thing different and it has zero impact on semi auto / full auto operation. If you are implying its somehow not kosher because of not having a BATFE approval letter it's picking nits from using established mods to disable the automatic operation by permanently modding certain parts and using a receiver that will not accept drop in FA parts.
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Old 11-16-2017, 12:14 PM   #13
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Quote:
Originally Posted by cal50 View Post
Please do tell.
I am doing a build similar but using standard AR fire control parts.

All the approved BATFE mods are performed like cutting off the auto sear, cutting off the sear notch on the carrier, milling down the carrier to fit the DSARMS receiver, transfer pin in carrier, etc. so the prior approved design parts and operation is not changed.

The hammer system is the only thing different and it has zero impact on semi auto / full auto operation. If you are implying its somehow not kosher because of not having a BATFE approval letter it's picking nits from using established mods to disable the automatic operation by permanently modding certain parts and using a receiver that will not accept drop in FA parts.
No, he was just saying Naolith "nailed" was gonna bitch cause pic sizes lol
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Old 11-16-2017, 01:27 PM   #14
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I resized the first pics to the 97Kb max size allowance, they were like thumbnails but would not post so I had to use the link method. Not sure what was the problem but because I needed to link the pics I didn't worry about size. I am not sure how guys embed videos so I linked that also.
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Old 11-16-2017, 04:17 PM   #15
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Quote:
Originally Posted by MIG*7.62 View Post
No, he was just saying Naolith "nailed" was gonna bitch cause pic sizes lol
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Old 11-16-2017, 04:24 PM   #16
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so when can i buy a conversion kit from you??
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Old 11-16-2017, 11:49 PM   #17
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Quote:
Originally Posted by raggedwhole! View Post
You are about to get NAILED.
They looked normal size on my PC, may be a little large on a cell phone. I was going to use the resize shortcut but didn't since the resolution was good.
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Old Yesterday, 01:49 PM   #18
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[IMG][/IMG]
[IMG][/IMG]
Fit a couple components, head spaced and pinned the barrel. Trigger has nice crisp let off with no creep and just over 4# pull. Uses factory safety.
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