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MG-42 BRP Build

Ask your build questions here. Welding, assembly, etc.
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oakrodent
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MG-42 BRP Build

Postby oakrodent » Sat Nov 07, 2009 8:25 am

I decided show a step by step build of one of my BRP receiver. I have built a few of these and this is how I do them. I am not saying it is the only way, but it’s the way I do them and they all have worked without a flaw. I also don’t use rivets. I have used them my whole life. From using them on a large farm in the Midwest when I was going up to aircraft in the military to gas turbines in the power industry. Rivets are hard to do correctly. I have done millions of them. Even if you get them tight, sometimes they become loose. This is a flaw I am not happy with. I weld everything. When my MG42’s are done they have all the correct rivet heads in all the correct places, inside and out and it is quite easy to do. I will show every step for you first time builders. I will have this one completed in under a month. I measure everything in millimeters. All my tools are standard.
Attachments
Pic 1.JPG
1- Lay out all your parts. I remove the bolts that hold the feed cover latch and barrel door latch. I then retap the holes and chase the threads of the screw. If there is a problem now is the time to catch it. You want do completely disassemble the Mg after you test fire so it can be sandblaster and blued.
Pic 2.JPG
2- Lay out semi auto bolt block location on the bottom of the receiver. I also mark the block for the correct installation direction
Pic 3.JPG
3- Proper set up before milling is key! Make sure you are level
Pic 4.JPG
4- Mill notch
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Re: MG-42 BRP Build

Postby oakrodent » Sat Nov 07, 2009 8:30 am

Steps 5 - 8
Attachments
Pic 5.JPG
5- Weld in the semi auto block. I use a Miller 210 mig welder with 0.023 wire.
Pic 6.JPG
6- Grind welds flush.
Pic 7.JPG
7- Mill charging handle groove in ratchet plate. I use a 3/32 keyseat cutter to cut this in the middle of the dimples.
Pic 8.JPG
8- Trial fit the charging handle in ratchet plate. You will have to mill the bottom of the ratchet plate for clearance.
Pic 9.JPG
Pic 10.JPG
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Re: MG-42 BRP Build

Postby oakrodent » Sat Nov 07, 2009 8:33 am

Steps 9 - 12
Attachments
Pic 11.JPG
9- Lay out charging handle slot on the receiver. Don’t do the charging handle cut out yet.
Pic 12.JPG
10- Machine the slot in the receiver. MAXIMUM slot depth is 2.5mm
Pic 13.JPG
11- Measure the distance between the top of the ratchet plate groove to the bottom of the charging handle slot. Measurement “A” mine is 15mm
Pic 14.JPG
12- Disassemble charging handle. If you are using a mill, remove the button on the end
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Re: MG-42 BRP Build

Postby oakrodent » Sat Nov 07, 2009 8:36 am

Steps 13 - 16
Attachments
Pic 15.JPG
13- Machine charging handle using measurement 11A (step 11 measurement A) Mine is 16.5mm before milling. I removed 1.5mm from 2 locations. Also square the inside bend of the charging handle for the semi auto bolt.
Pic 16.JPG
Pic 17.JPG
14- Lay out charging handle cut out.
Pic 18.JPG
15- Mill charging handle cut out. You will need to rotate the receiver to complete the cut out.
Pic 19.JPG
Pic 20.JPG
16- Clean up the cut out and slot. Trial fit charging handle.
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Re: MG-42 BRP Build

Postby oakrodent » Sat Nov 07, 2009 8:39 am

Steps 17 - 21
Attachments
Pic 21.JPG
17- I sandblast all parts that are welded / riveted to the receiver. I then spray them with gun oil to prevent rusting
Pic 22.JPG
18- Lay out the holes for the rear barrel guide / barrel door bracket on both sides. Drill the 8 marked holes with a ¼ drill bit. Drill the barrel door rivet holes with a 15/64 drill bit. Clean all burrs
Pic 23.JPG
19- Clamp in your upper or lower bracket. The upper and lower brackets are not the same. The barrel door rivet holes are off set. Before you clamp in the bracket put a 15/64 drill bit threw the barrel door rivet holes to align the bracket.
Pic 24.JPG
20- Weld the bracket to the receiver. Repeat steps 19 and 20 for the other bracket.
Pic 25.JPG
21- Grind welds flush and smooth
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Re: MG-42 BRP Build

Postby oakrodent » Sat Nov 07, 2009 8:43 am

Steps 22 - 27
Attachments
Pic 26.JPG
22- Cut 3 large rivets to the same thickness as the front barrel stop
Pic 27.JPG
23- Drill out the 3 rivet holes in the receiver for the front barrel stop to a 3/8 hole. Clean and deburr holes.
Pic 28.JPG
24- Install front barrel stop into the receiver. If you have to hit anything with a hammer when building the MG-42 use a brass drift.
Pic 29.JPG
25- Mark a line on your barrel bearing. This is a very important setting for the correct location of the front barrel stop.
Pic 30.JPG
26- Install all 3 cut rivets on the inside of the front stop. Install the barrel bearing and barrel. Move the barrel forward until the line on the barrel bearing can be seen on the outside of the front receiver bushing. The line should be even with the front bushing. The barrel stop should be seated square on the barrel.
Pic 31.JPG
27- Weld the front barrel stop to the receiver and grind the welds down flush and smooth.
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Re: MG-42 BRP Build

Postby oakrodent » Sat Nov 07, 2009 8:48 am

Steps 28 - 33
Attachments
Pic 32.JPG
28- You may need to make some adjustments to these tabs to get the barrel to fit.
Pic 33.JPG
29- Extend a line from the front of the trunnion cut out to the top of the receiver. Measure from this line to the back of the trunnion stop 29C Mine is 19mm
Pic 34.JPG
30- Measure trunnion opening on the receiver. Mine is 20mm x 32mm
Pic 35.JPG
31- Measure front of cam to front of trunnion 31D mine is 20mm also measure trunnion cam size. Mine is 20mm x 33mm
Pic 36.JPG
32- 31D – 29C = 32E Mark out the trunnion cut out. Remove 32E from the front of the trunnion . I have to remove 1mm
Pic 37.JPG
33- Machine out you trunnion . My trunnion cam is 20mm x 33mm so I machined out my opening to 21mm x 34mm. Ensure you have .5mm clearance around your cam area.
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Re: MG-42 BRP Build

Postby oakrodent » Wed Dec 09, 2009 4:23 pm

Steps 34 -35
Attachments
Pic 38.JPG
34 - Install your trunnion . You may need to remove a small amount of material from these areas to get the trunnion fit.
Pic 39.JPG
35 - When the trunnion is installed, it should be up against the trunnion stops. I also cut the bolt. I leave 2 threads showing. They are needed later so don’t cut it any shorter.
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Re: MG-42 BRP Build

Postby oakrodent » Wed Dec 09, 2009 4:57 pm

Steps 36 - 40
Attachments
Pic 40.JPG
36 - To rivet the barrel door I use a C-clamp with two cut washers to lock the front foot.
Pic 41.JPG
37 - Install barrel door and rivet. After riveting open and close the door a few times to loosen it up.
Pic 42.JPG
38 - Install barrel door latch. Close door and ensure it latches.
Pic 43.JPG
39 - Install the barrel bearing and barrel. Ensure the door latches properly and the barrel moves freely back and forth. If the barrel is hard to move check these areas for interference. Also if the door is hard to latch when the barrel is properly seated all the way down and the barrel is hard to move back and forth you may need to also remove a small amount of material from the barrel pads on the barrel door latch. The best way to check this is to slightly unlatch the door. The barrel will them move freely. Be carful not to remove too much!
Pic 44.JPG
40 - Stand receiver up and measure from the barrel bearing to the front receiver bushing with the barrel in the full back position. You should have around 8mm
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Re: MG-42 BRP Build

Postby oakrodent » Wed Dec 09, 2009 5:09 pm

Steps 41 - 45
Attachments
Pic 45.JPG
41 - The lower buffer tab is smaller than the upper tab.
Pic 46.JPG
42 - The front of the tabs are going to be installed flush with the back of these machined grooves. This is very important!
Pic 47.JPG
43 - Set the lower tab in its correct position and mark the location of the buffer latch stud along with an arrow pointing forward. The tabs are too long and will be cut to the correct size after they are welded in.
Pic 48.JPG
44 - Drill a ¼ hole for the latch stud. I also put a 3/8 counter bore on the inside for a better weld. Also mark the tab to show that the flat side of the stud goes on the right side of the receiver.
Pic 49.JPG
45 - Weld the stud to the tab and grind the weld flush.
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Re: MG-42 BRP Build

Postby oakrodent » Wed Dec 09, 2009 6:05 pm

steps 46 - 51
Attachments
Pic 50.JPG
46 - Measure distance from the outside of the receiver to the inside rear machined groove. 46E
Pic 51.JPG
47 - Drill out the two lower buffer tab rivet holes and the two upper ones also with a 3/8 drill bit.
Pic 52.JPG
48 - Clamp in the lower tab and weld. MAKE SURE you are flush with the machined groove.
Pic 53.JPG
49 - Clamp in the upper tab and weld. Again make sure you are flush with the machined groove. Grind all welds flush
Pic 54.JPG
50 - Measure in 46E from the outside of the receiver and mark the tabs to be cut.
Pic 55.JPG
51 - Cut tabs with a small cut off wheel.
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Re: MG-42 BRP Build

Postby oakrodent » Wed Dec 09, 2009 6:10 pm

Steps 52 and 53
Attachments
Pic 56.JPG
52 - Install the buffer assy. If it is hard to slide in, check to see if the walls are square. If not put receiver into a vice and adjust. The buffer should slide in easily. When you turn the buffer and it is hard to turn. Check to make sure the tabs are not in the machined groove area.
Pic 57.JPG
53 - Mill a 3/16 hole 6 mm deep 10mm from the back of the receiver for the buffer latch spring.
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Re: MG-42 BRP Build

Postby oakrodent » Wed Dec 09, 2009 6:15 pm

Steps 54 - 58
Attachments
Pic 58.JPG
54 - Machine this area only so the opening is 18mm wide for the trigger housing.
Pic 59.JPG
55 - Drill 3/8 holes in these three areas.
Pic 60.JPG
56 - Cut one large recessed rivet to the same thickness as the trigger bracket/recoup stop.
Pic 61.JPG
57 - Cut your recoup to match the top one.
Pic 62.JPG
58 - This is the correct orientation for the front recoup bolt.
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Re: MG-42 BRP Build

Postby oakrodent » Wed Dec 09, 2009 6:20 pm

Steps 59 - 64
Attachments
Pic 63.JPG
59 - You need to drill out the front recoup hole with a 7/32 drill bit. Then install the recoup. Make sure the recoup is turned down so the tabs are down against the receiver.
Pic 64.JPG
60 - Install trigger bracket/recoup stop
Pic 65.JPG
61 - Install trigger housing
Pic 66.JPG
62 - Pin the trigger housing to the bracket and push the trigger bracket/recoup stop up against the back of the recoup.
Pic 67.JPG
63 - Install the cut recessed rivet into the bracket and weld the bracket to the receiver. After you weld the rear bracket rivet hole, you will have to remove the trigger housing to weld the two remaining holes.
Pic 68.JPG
64 - Grind down all the weld. Drill out the rear recoup bolt hole with a 7/32 drill bit. Install rear recoup bolt and tighten nut.
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Re: MG-42 BRP Build

Postby oakrodent » Wed Dec 09, 2009 6:28 pm

Steps 65 - 68
Attachments
Pic 69.JPG
64 - Cut 15 small rivets to the same thickness as the rail. I use an old piece of rail.
Pic 70.JPG
68 - Left and right rails are not the same. The left rail has one thinner rail. One is 2mm and the other is 3.5mm Both rails on the right side are 3.5mm You can use 2 left rails. Mark your rails left and right.
Pic 71.JPG
67 - Lay out your holes for your rails. They should be on the rails center line. When marking out your holes, you want the rails stops tight against the receiver. Use a 5/32 drill bit for the holes.
Pic 72.JPG
68 - I made a simple way to hold the rivets tight in the rails so the rails can be welded tight against the receiver. Make sure you cut it so it can push on the rivet and has clearance for the middle bolt tabs. I used two 3/8-16 x ¾ bolts, one 3/8-16 nut, and one 3/8-16 coupler nut.
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Re: MG-42 BRP Build

Postby oakrodent » Wed Dec 09, 2009 6:33 pm

Steps 69 - 73
Attachments
Pic 73.JPG
69 - Drill out these 3 holes on both sides of the receiver with a 3/8 drill bit.
Pic 74.JPG
70 - Install rails using four 6-32 x 1” bolts with nuts. MAKE sure the rails are centered on the trunnion.
Pic 75.JPG
71 - Install 1 set of rivets. Use the spreader to push them tight against the receiver.
Pic 76.JPG
72 - Weld in the rails when you installed the rivets. Continue steps 71 and 72 until all 3 holes are done.
Pic 77.JPG
73 - Remove the 4 bolts. Drill out the receiver with a 3/8 hole saw. Do not damage the rail. Use steps 71 and 72 to finish the rail rivet holes. Grind all weld flush when finished.
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Re: MG-42 BRP Build

Postby oakrodent » Wed Dec 09, 2009 6:56 pm

Steps 74 and 75
Attachments
Pic 78.JPG
74 - Check the rear of both rails to see if they extend into the front buffer lock grove. If they are, cut them back out of this area.
Pic 79.JPG
75 - Test fit the bolt head in the rails. It should move freely back and forth. If it doesn’t you have to correct this. I have a bolt head I accidently dropped awhile ago and broke off on of its tabs. I use this and a brass drift to adjust the rails. Hit the bolt from the bottom. Not the top.
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Re: MG-42 BRP Build

Postby oakrodent » Wed Dec 09, 2009 6:59 pm

Steps 76 - 79
Attachments
Pic 80.JPG
76 - Pin on the feed tray. It has to sit flat on the top of the receiver.
Pic 81.JPG
77 - This is the area that needs to be machined to get the feed tray down flat.
Pic 82.JPG
78 - I use a mill for this task. You can also use a grinder or a sanding disk.
Pic 83.JPG
79 - Install the feed cover latch and install the feed cover on the receiver. Feed cover should latch nicely.
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Re: MG-42 BRP Build

Postby oakrodent » Wed Dec 09, 2009 7:09 pm

Steps 80 - 84
Attachments
Pic 84.JPG
80 - Lay out your holes for the front sight assy on both sides of the receiver. Measure from the front of the receiver bushing back. The flash hider lock hole is 68mm and the fight is 88mm. Measure 4mm up from the flat area.
Pic 85.JPG
81 - Use a 5/32 mill to drill these holes. A drill bit will walk too much to get things straight. Lay out and set up is very important for this step.
Pic 86.JPG
82 - Mark out the slot for the sight assy. It is 13mm wide. Mill out this area.
Pic 87.JPG
83 - When milling out the slot, mill it even with these two areas. They are not on the same level. The flash hider lock is lower.
Pic 88.JPG
84 - Make sure the slot is only slightly wider than the sight assy. Don’t remove too much material.
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Re: MG-42 BRP Build

Postby oakrodent » Thu Dec 10, 2009 5:02 pm

Steps 85 - 89
Attachments
Pic 89.JPG
85 - Mark out the two mill lines.
Pic 90.JPG
86 - Using a cut off wheel open up the slot to the lines you marked.
Pic 91.JPG
87 - You want a nice bevel, not a flat edge.
Pic 92.JPG
88 - Test fit your flash hider lock bar. I use a 5/32 drill bit. Lift the bar up and measure to the front receiver bushing. You should have 20mm
Pic 93.JPG
89 - If your lock does not lift to the correct measurement. Remove some material from this area.
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