MG-42 BRP Build
MG-42 BRP Build
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.
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- 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.
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- 2- Lay out semi auto bolt block location on the bottom of the receiver. I also mark the block for the correct installation direction
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- 3- Proper set up before milling is key! Make sure you are level
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- 4- Mill notch
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Re: MG-42 BRP Build
Steps 5 - 8
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- 5- Weld in the semi auto block. I use a Miller 210 mig welder with 0.023 wire.
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- 6- Grind welds flush.
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- 7- Mill charging handle groove in ratchet plate. I use a 3/32 keyseat cutter to cut this in the middle of the dimples.
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- 8- Trial fit the charging handle in ratchet plate. You will have to mill the bottom of the ratchet plate for clearance.
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Re: MG-42 BRP Build
Steps 9 - 12
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- 9- Lay out charging handle slot on the receiver. Don’t do the charging handle cut out yet.
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- 10- Machine the slot in the receiver. MAXIMUM slot depth is 2.5mm
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- 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
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- 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
Steps 13 - 16
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- 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.
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- 14- Lay out charging handle cut out.
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- 15- Mill charging handle cut out. You will need to rotate the receiver to complete the cut out.
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- 16- Clean up the cut out and slot. Trial fit charging handle.
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Re: MG-42 BRP Build
Steps 17 - 21
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- 17- I sandblast all parts that are welded / riveted to the receiver. I then spray them with gun oil to prevent rusting
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- 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
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- 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.
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- 20- Weld the bracket to the receiver. Repeat steps 19 and 20 for the other bracket.
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- 21- Grind welds flush and smooth
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Re: MG-42 BRP Build
Steps 22 - 27
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- 22- Cut 3 large rivets to the same thickness as the front barrel stop
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- 23- Drill out the 3 rivet holes in the receiver for the front barrel stop to a 3/8 hole. Clean and deburr holes.
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- 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.
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- 25- Mark a line on your barrel bearing. This is a very important setting for the correct location of the front barrel stop.
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- 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.
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- 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
Steps 28 - 33
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- 28- You may need to make some adjustments to these tabs to get the barrel to fit.
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- 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
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- 30- Measure trunnion opening on the receiver. Mine is 20mm x 32mm
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- 31- Measure front of cam to front of trunnion 31D mine is 20mm also measure trunnion cam size. Mine is 20mm x 33mm
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- 32- 31D – 29C = 32E Mark out the trunnion cut out. Remove 32E from the front of the trunnion . I have to remove 1mm
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- 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
Steps 34 -35
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- 34 - Install your trunnion . You may need to remove a small amount of material from these areas to get the trunnion fit.
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- 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
Steps 36 - 40
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- 36 - To rivet the barrel door I use a C-clamp with two cut washers to lock the front foot.
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- 37 - Install barrel door and rivet. After riveting open and close the door a few times to loosen it up.
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- 38 - Install barrel door latch. Close door and ensure it latches.
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- 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!
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- 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
Steps 41 - 45
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- 41 - The lower buffer tab is smaller than the upper tab.
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- 42 - The front of the tabs are going to be installed flush with the back of these machined grooves. This is very important!
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- 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.
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- 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.
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- 45 - Weld the stud to the tab and grind the weld flush.
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Re: MG-42 BRP Build
steps 46 - 51
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- 46 - Measure distance from the outside of the receiver to the inside rear machined groove. 46E
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- 47 - Drill out the two lower buffer tab rivet holes and the two upper ones also with a 3/8 drill bit.
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- 48 - Clamp in the lower tab and weld. MAKE SURE you are flush with the machined groove.
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- 49 - Clamp in the upper tab and weld. Again make sure you are flush with the machined groove. Grind all welds flush
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- 50 - Measure in 46E from the outside of the receiver and mark the tabs to be cut.
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- 51 - Cut tabs with a small cut off wheel.
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Re: MG-42 BRP Build
Steps 52 and 53
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- 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.
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- 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
Steps 54 - 58
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- 54 - Machine this area only so the opening is 18mm wide for the trigger housing.
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- 55 - Drill 3/8 holes in these three areas.
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- 56 - Cut one large recessed rivet to the same thickness as the trigger bracket/recoup stop.
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- 57 - Cut your recoup to match the top one.
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- 58 - This is the correct orientation for the front recoup bolt.
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Re: MG-42 BRP Build
Steps 59 - 64
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- 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.
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- 60 - Install trigger bracket/recoup stop
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- 61 - Install trigger housing
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- 62 - Pin the trigger housing to the bracket and push the trigger bracket/recoup stop up against the back of the recoup.
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- 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.
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- 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
Steps 65 - 68
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- 64 - Cut 15 small rivets to the same thickness as the rail. I use an old piece of rail.
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- 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.
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- 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.
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- 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
Steps 69 - 73
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- 69 - Drill out these 3 holes on both sides of the receiver with a 3/8 drill bit.
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- 70 - Install rails using four 6-32 x 1” bolts with nuts. MAKE sure the rails are centered on the trunnion.
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- 71 - Install 1 set of rivets. Use the spreader to push them tight against the receiver.
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- 72 - Weld in the rails when you installed the rivets. Continue steps 71 and 72 until all 3 holes are done.
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- 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
Steps 74 and 75
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- 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.
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- 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
Steps 76 - 79
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- 76 - Pin on the feed tray. It has to sit flat on the top of the receiver.
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- 77 - This is the area that needs to be machined to get the feed tray down flat.
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- 78 - I use a mill for this task. You can also use a grinder or a sanding disk.
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- 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
Steps 80 - 84
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- 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.
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- 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.
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- 82 - Mark out the slot for the sight assy. It is 13mm wide. Mill out this area.
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- 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.
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- 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
Steps 85 - 89
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- 85 - Mark out the two mill lines.
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- 86 - Using a cut off wheel open up the slot to the lines you marked.
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- 87 - You want a nice bevel, not a flat edge.
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- 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
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- 89 - If your lock does not lift to the correct measurement. Remove some material from this area.
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