And so it begins......more to follow.

Ok , some basic grunt work getting the DPM back together since you need it in one piece before getting a fire control system in it. I combined a mix of DPM-28 parts sets with an intact front section and shroud and a nice back half.
I used the grip frame for an alignment jig / guide to position the rear section. I started by using copper backing pieces inside and tacking and welding the rear section from the middle out doing the top section last. I inserted an .008" shim between the grio frame to allow for weld shrink. I used TIG welding and ER70-S2 filler rod.



[Imgur]https://(https://i.imgur.com/tHnwHkQ.jpg?1)

My top section was cut pretty wide so I made a copper backer to match the DPM receiver angle.

Getting better~

After I got the rear stub where it fits the grip frame I needed to set the headspace on the front section and weld it. I used a DPM barrel stub with a copper collar on the chamber end with an added .010" to allow for weld shrink. The receiver sections were ground out to the root to clear my TIG electrode and welded from the root up for 100% overlapping coverage,

I have an original DPM barrel from Bowman and one I got with one of my parts set. The Bowman barrel ( new Polish factory DPM ) fits and headspace's perfect. The aftermarket barrel I got with the parts set LOOKED like a DPM barrel but it was REALLY screwed up . I still do not know if I "saved" it but long story short the chamber clearance is wrong along with the gas hole location and radial orientation. I had to mill clearance in the chamber area to allow the extractor to grab the case and the top section of the barrel to allow the bolt to close. Once I fixed these the gas port hole was overclocked and I used a ball endmill to mill a channel to the correct gas block location.
I had to TIG up the barrel lock slot and re-cut it in the correct spot.

I now have the receiver working with the necessary denial features and two head spaced barrels.On to the trigger group~
I cut the stock grip off the DPM-28 grip frame. I drilled a series of 1/8" holes along the line I wanted to remove it from.
Stock~




Now that I have them separated I cut a filler slug and TIG welded it inside the grip frame to fill in the old features. I pressed the slug in and welded it.

I slotted the "slug" to clear the HK hammer width.Next up was fitting the mounting busing that is welded in the grip frame. Not a hard thing to do but its on a slight radius cutting thru a weld. I spot faced it with an endmill then center drilled, drilled and reamed it so the bushing is straight. Its press fit in the DPM frame , centered then TIG welded in place. The front was measured then set and welded .

Next up is modifying the recoil spring guide and making a firing pin transfer bar.

A little more progress.Working six days a week cuts into weapon build time. I HATE welding in a cold garage too!

Progress!
With limited play time I was tracking down an inconsistent ignition problem.I finally got it figured out and 100% ignition with all ammo , military surplus and commercial.
Details of the finished fire control group to follow.....

I doubt the stock G3 hammer spring has enough oomph to light up 54r military primers. I purchased a like new / used complete G3 trigger housing from RTG parts and the hammer spring seems a little weak. Not sure if it had been used / weak but swapping out coil hammer springs is easy and takes about a minute. I am using the extra force hammer spring from HK parts.

https://hkparts.net/product/hk-308-223-hammer-spring-extra-power-p16447.htm

Updated link 12/21/20





The real source / problem of my ignition issue was in my hammer to transfer pin assembly length. I am using the DPM firing pin and parts modified. Firing pin has a fixed stop internally for travel and over travel. The bolt rides in the slide and when it chambers a round the the bolt stops and locking flaps engage. I WRONGFULLY  assumed that slide made contact with the back of the bolt when chambered / fully forward. Its next to impossible to see inside so I was convinced my problem was something else. My fix was making the transfer pin ( the pin the hammer makes contact with and hits the back of the firing pin) about .050" longer and 100% ignition.


Its harder to explain but clear when I can post some detail pics and video.
Now to pretty it up and test fire.

Random pics ahead~


Lower receiver mods and G3 grip frame fitting is straight forward. I need to add some steel side plates to cover the stock DPM safety holes and make a smooth transition to the G3 housing.  Hammer is shortened to clear the recoil spring. Face was cut to square up the contact angle when impacting the transfer pin.

This is the system in a nutshell.
The stock DPM firing pin is cut in half forward of the angled surface that opens the locking flaps. I used a band saw.
Once cut in half I face the rear of the firing pin , turned the firing pin nose down to .073" diameter and bushed the bolt face.
This will eliminate any chance of primer flow.


The back section that the recoil spring rides on has a .250 slot milled thru the bottom up to the shoulder, I then used a ball end mill and opened up the slot bottom to clear the transfer pin. I put a .188" hole thru for the transfer pin to slide thru and make contact with the firing pin.

A spring spacer is turned and slotted for the transfer pin to ride in.

My tranfer pin is a standard alloy steel dowel pin (solid) with a tab TIG welded on the bottom cut from a grade 8 bolt.
Its .235" wide and rides in the .250" wide milled slot in the recoil spring guide.


The rear of the receiver needs a clearance slot cut to clear the transfer in "heel".
Check for full travel.


Adding the spring spacer the recoil spring retainer (part that goes in the rear of the grip frame receiver will need clearance.

Random bolt pics ~

HK trigger group~

https://www.robertrtg.com/store/pc/G3-STEEL-SEF-LOWER-COMPLETE-GREEN-GRIP-40p7101.htm

Extra force Hammer spring~

https://hkparts.net/product/hk-308-223-hammer-spring-extra-power-p16447.htm


Semi Sear spring~

https://hkparts.net/product/semi-elbow-spring-for-trigger-pack-match-grade-p18002.htm



Links updated 12/20/20

Wrapping up a few small details before test fire.
Cut filler plates for the sides of the DPM grip frame to smooth out the transition between it and the G3 housing. Used a .125" carbide end mill to make a nice small radius in the corners for  appearance.
NOT pretty~

Pretty~




Stock recoil spring retainer and mine faced off to clear my recoil spring spacer~

Small stuff to wrap up and ready for test fire shortly.
Welding the side plates on the grip frame was cosmetic but every time you weld something , something moves. In my case I tacked the sides ( not cleaned up yet) and put a few beads on the underside edge.I was not feeling good about a few staggered welds and used low amps and ran beads down both sides alternating and letting it cool. Finished up letting it cool down and tried it on my receiver and it was not close to fitting. The heat pulled down the frame and warped it. I figured as much and 5 minutes of tweaking got it straightened out. Amazing forces at work when welding......

Ground the remainder of the stock pistol grip off and smoothed it up a little but not done,



Look, no more ugly unused side holes~

Proof of life......

My apologies for dragging this build out WAY longer than I ever anticipated.

I was interrupted by a few must do home projects and a crazy work schedule. Anyway, it is alive!

When I stopped work on it the last time I left it in a spot where I thought I had an quick test fire then a victory dance.That did not happen. When I did the work and layout for the trigger system I wrongly assumed the recoil / slide travel. I had assumed it traveled to the full length of the slide but in actuality it does not. My key stock welded to the bottom of the slide is what cocks / resets the hammer . I had no issues with ignition but when I test fired it the hammer was not resetting.

It was an easy fix by cutting off the piece of key-stock I originally welded to the slide and replacing it with a longer one. I also added clearance in the grip frame to clear the longer piece of key-stock , also easy.

When that was done I ran into a new problem : Out of ammo.Ammo cost and availability is bad and I had to wait to find some more Wolf ammo. Target Sports  came thru and after a wait I snagged a half case of ammo. Now I was again excited that I had it in the bag but another twist. I had a self imposed problem with my mags , I cleaned and tore apart all of them and over wound the springs in all of them so that was an easy one to fix.

The last problem I discovered was my gas setting.The stock gas valve has three setting and gas hole sizes.

Small    .106"

Medium .131

MAX     .158

I had read on some conversions the barrel port and valve needed to be run at .187" diameter for cycling.I tried the stock (.158) gas setting and it was close to running but not reliable. I got the idea to just open up the barrel port and valve to .187" and claim victory. Well I did that and my gun was WAY over gassed and would not run. It was close to tearing rims off but the bolt and carrier was coming back so hard it was just riding over the case rim.

Today I modified one of the other valve ports to .170" diameter and it runs like a raped ape.Smooth cycling and no case damage or other surprises.
I will add pics of the re-worked slide , key stock and grip frame clearance.On my to-do before I make it pretty is to add a bolt stop that I can engage , it makes mag and barrel changes WAY easier. Its going on the left side of the receiver. I also need to test fire my spare rescued barrel.

The DPM is one hell of a 7.62X54r launcher.The G3 trigger set up may not be for everyone but it allows the builder to have an inexpensive trigger that works with most of the parts in your DPM parts set.

Pics of added clearance and lengthened key stock.

Added clearance is to make sure added key stock does not impact frame.





Slot for keystock just kisses the slide surface and is milled full length to the front of the slide.TIG welded on the front face , rear face and mid length.





Key stock ( after welding ) is milled to the height shown , from the top of the key stock to the slide surface .



After looking at everything in retrospect the spring spacer could be made shorter in length. Its .566" long and adds load to the stock recoil spring. If this was shorter it may run on the stock (large) gas setting.Mine runs prefect with the gas regulator drilled out to .175" diameter.

Transfer pin dimensions~

Great thread!

The DP / DPM is an excellent semi conversion project , they are drying up.

DP28 , still kicking ass today~

https://twitter.com/UAWeapons/status/1532282866293518336

Wow, great fabrication skills!