HOW-TO: Convert Umarex MP5 SD -> A5 and SBR the Umarex MP5 A5
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Thread: HOW-TO: Convert Umarex MP5 SD -> A5 and SBR the Umarex MP5 A5

  1. #1
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    Default HOW-TO: Convert Umarex MP5 SD -> A5 and SBR the Umarex MP5 A5

    So, you want to turn this:
    HOW-TO: Convert Umarex MP5 SD -> A5 and SBR the Umarex MP5 A5-pic6.jpg
    Into this?
    HOW-TO: Convert Umarex MP5 SD -> A5 and SBR the Umarex MP5 A5-pic7.jpg
    Or Maybe Even This?
    HOW-TO: Convert Umarex MP5 SD -> A5 and SBR the Umarex MP5 A5-pic8.jpg

    These instructions are for converting an Umarex H&K MP5 SD model into an A5 model (if you already have an MP5 A5 and just want to SBR it skip to the last section). You may want to ditch your SD for an A5 for one or more of the following three reasons:

    1. It is currently impossible to attach the Tri-rail tactical forearm for the HK MP5 .22LR to the SD version.
    HOW-TO: Convert Umarex MP5 SD -> A5 and SBR the Umarex MP5 A5-pic1.jpg
    2. It is difficult to SBR the SD model, and even if it was done, it would look awkward as the SD model by design has a silencer attached.
    3. You are tired of the SD and would rather have the more ubiquitous MP5 A5 (or A4 by adding the fixed stock).

    To convert the SD to an A5, one needs to acquire the following parts from Umarex/Walther:

    1. A5 Forearm 578.30.01.1 (Do NOT buy this if you are going to use the railed forearm, but it instead)
    2. Cocking lever tube 578.30.02.1 (Do NOT let Umarex talk you into buying the entire assembly part 578.30 or any of the other cocking lever tube parts since you already have all the internal parts in your existing SD cocking lever tube AND you have to pull all the parts out anyways to put in the screw it saves no time you just end up with extra parts for no reason).
    3. Front sight assembly 578.70.20
    4. Push pin 578.30.09
    5. Lug tube 578.50.03.1 (Do NOT buy this if doing the 416 pistol SBR option)
    6. O-ring 578.50.05.3 (Do NOT buy this if doing any SBR option)
    7. A5 compensator/faux can 578.51.05 (The SD faux silencer will not fit properly on an A5, so it is recommended you buy the A5 faux silencer. Do NOT buy this if doing any SBR option)
    8. Sight screw 578.70.24.1 (Do NOT let Umarex tell you this part is a mistake in the schematics, it is NOT a mistake, and it is a critical part. They will insist that it is not necessary but they are wrong, their internal schematics are wrong—the customer supplied schematics are proper).
    If you are converting to an SBR as part of this, you have additional parts that will be necessary, see the SBR section below.

    To ensure that you end up with the right cocking lever tube for the A5, I highly recommend that you ask to speak to Dallas at Umarex customer service/parts. He is the only one there that knows first hand the difference between the two. The problem, like several items at Umarex, is they are mislabeled in the back. I had to exchange this part 4 times before getting the right part, each time they would send out an SD cocking lever tube which I already had, and then they would argue with me that it was the right one. Dallas will either send the right one or will tell you the right one is out of stock, you won’t get the wrong part from him.

    Once you have the parts, dismantle the existing SD:
    1. Unscrew the faux compensator.
    2. Unscrew the two hex screws that are directly below the front sight. Only unscrew the two that are directly below and closest to each other, not the two that are halfway down on the edges as that will dismantle the handgrip which is not what you want.
    3. Once unscrewed the user can slide off the SD handgrip.
    4. Field strip the weapon
    5. Now the entire inner metal frame will slide out through the back of the weapon where the stock piece goes on. This includes the bolt, barrel, etc. leaving just the black sleeve jutting out of the black outer frame.
    6. Set aside the metal frame with the barrel as nothing is going to be done with this unless the user is converting to a SBR, in which case follow those separate instructions below later when instructed.
    7. Unscrew all of the hex screws that connect the black metal outside frame together, there are a total of 4. If the user has one of the aftermarket top rails installed, that will need to be removed as well as it will prevent the frame from splitting apart.
    8. After all of the screws have been removed, carefully separate the two halves of the black outer frame. Take care to catch the parts from the magazine release that will fall out, there will be two parts that will come loose and fall out, the remaining parts will remain intact unless they are unscrewed--which is unnecessary.
    9. At this point, if one is converting to an SBR, remove the black sleeve that surrounded the barrel and complete the SBR instructions below, once done, come back and start at the next step, #10.
    10. Remove the cocking lever tube from whichever black frame half it resides in.
    11. Using a 3/32 punch, drift out the pin that is holding the cocking lever handle in place, visible when the handle is turned into its bolt hold open position; pulled furthest back. Once that pin is out, the entire contents of the cocking lever tube can be dismantled. While not complicated, it is important to note how these parts were situated inside the tube as you will be reinstalling all of these parts into the A5 tube.
    12. If desired, and recommended if they are at all dirty, degrease/clean off all of the cocking lever tube parts and reapply grease where it was previously present.
    13. Insert the sight screw into the newly supplied A5 cocking lever tube with a very long screwdriver preferably one with a magnet. Once you’ve pushed it successfully through the hole at the far end of the cocking tube, attach the front sight assembly to the cocking lever tube. You may want to apply some loctite to the end of the screw before putting it into the front sight assembly. The factory installation does have some loctite equivalent installed.
    14. Take the sight assembly and attached cocking lever tube from Umarex and put the parts cocking lever tube back in, in exactly the same positions that they were in the SD cocking lever tube.
    15. Drift the pin back in the cocking lever handle.
    16. Take the A5 cocking lever tube fully assembled with front sight assembly and put it in place on the frame where the SD cocking lever tube was previously. At this point you will have to make sure that the barrel sheath (the black tube the barrel sits in) is properly in place because it also attaches to the bottom of the sight assembly. If you forget to do this, you will end up having to dismantle the entire thing and come back to do this as it won’t be able to fit it in afterwards even though it looks like you might be able to.
    17. Put the two parts from the magazine release back in place; see schematics if unclear.
    18. Screw back together the black frame with cocking lever tube, sleeve and magazine release parts all installed. Install the handguard either the A5 version with the pushpin or a tri-rail handguard if purchased.
    19. If you did an SBR using a 416 pistol barrel option NOT the custom length option, skip to step #21.
    20. Put the lug tube over the sleeve and slide it into the front sight, make sure its small indent lines up with the indent on the front sight so that it is indexed properly and will not rotate around. Put the o-ring on after if using a faux compensator.
    21. Regardless of option chosen, all of these will be loose until the barrel and metal frame are installed back into the black frame and either the compensator is screwed onto the barrel or an adapter. Reassemble the rest of the weapon from field strip state to full functional state. Once the weapon is back together either screw on the A5 compensator/fake silencer OR use an M8x.75 ->1/2x28 adapter if you were an SBR conversion. You are now done.

    Short Barrel Rifle (SBR) conversion

    HOW-TO: Convert Umarex MP5 SD -> A5 and SBR the Umarex MP5 A5-pic2.jpg

    Prior to doing any part of these instructions you must have a tax stamp from the ATF for the weapon you plan to convert. Doing so without an approved Form 1 is against the law and is a very serious crime, which will likely result in a long jail sentence and a total lifetime loss of your firearm rights, not to mention a whole world of other issues. While it certainly is cool to have a SBR MP5 .22LR, I can guarantee you that it is not enough fun to justify breaking the law.

    There are three primary ways to convert your Umarex/Walther H&K MP5 A5 .22LR into an SBR:
    1. Acquire and use the Umarex/Walther H&K 416 Pistol barrel.
    Pros: Simple, only requires cutting your sheath/sleeve and boring it out a little with a drill or dremel. Also pretty cheap seeing as you can sell your existing barrel to help recover the costs of your newly purchased barrel.
    Cons: It is not the proper length, it is short by ½ inch which translates to not being able to have enough room to put on the tri-lug. Also, the boring of the sleeve can be slightly tricky if you don’t have the proper skills and/or tools.
    2. Cut down your existing H&K MP5 A5 or SD .22LR barrel.
    Pros: Proper length, unlike the 416 pistol barrel option so it is more “authentic” looking. You also might be able to convince whoever cuts/threads your barrel to do the sheath work for you which would be simple for a gunsmith to do and make it look professional.
    Cons: More expensive than 416 pistol barrel since you have to spend almost as much money to cut down your existing barrel as it would cost to buy a new one, with nothing to sell to recoup costs against. You also can’t go back to the stock configuration without buying a brand new barrel.
    3. Acquire and use the Walther International version MP5 .22LR barrel and sheath.
    Pros: Definitely the most prestigious option, as the parts will be all original Walther and you will be one of maybe two or three in the United States with such a configuration. Everything will just fit together like a glove with no custom work at all. My favorite benefit of this is you also get a muzzle nut that fits on, a part which you simply cannot buy in the U.S. at all, and you won’t be able to “cut down” anything to get it. The muzzle nut allows you to have the SBR’d MP5 look great without an ugly adapter on the end of the barrel when not using a suppressor.
    Cons: Not for the faint of heart as it is a royal PITA to get these parts with export/import laws, uncooperative seller, possible legal risks in the US and Europe, etc. Not worth even contemplating unless you have strong connections in Europe that you can use as a third party or have another full proof scheme. It is also incredibly expensive to buy and ship the parts.

    Those are listed in the order of complexity and expense, but probably also in reverse order of authenticity of the original, elegance of the conversion and desirability.


    To convert to an SBR, you need to buy the following parts:

    For option #1: You only need to buy the HK416 .22LR pistol barrel from Umarex, part #576.52.02 which was $116 as of 1/24/14. Since this option will require you to cut your existing sheath but not your barrel, you might want to consider buying a replacement sheath so that if you want to go back to the original configuration at any time you can. It is part #578.51.01.1 and cost $33 as of 1/24/14. If they are out of stock on the barrels, which happens from time to time, you can sometimes find one on the used market or you can do option #2.

    For option #2: Instead of buying a part, you will need to get your existing barrel cut down and re-threaded M8x0.75. TROS is one such place that does this and it should cost $88 for this service as of 1/24/14, with a 5-6 week turn around. You need to have Mark make the barrel 228mm which is almost exactly 9 inches. I have not asked Mark if he will cut/bore out the sleeve/sheath.

    Both option #1 & #2 need to buy one of the many M8x0.75->1/2 x 28 adapters not only so you can use a silencer, but to keep the barrel and sheath properly lined up otherwise the barrel will be loose inside the sheath and you can forget hitting a coke can at 10 yards. These are sold by HKParts, Gemtech, SilencerCo to name a few. There are two main styles of these adapters, for lack of a better name, the “HKParts” variety and the “Silencerco” variety. Gemtech carries both. The HKParts variety has the female threads sitting inside the male 1/2x28 threads, so it is a shorter adapter. It was designed for the HK416 rifles. The SilencerCo is longer, it was designed for the Walther P22. The SilencerCo more closely represents the adapter Walther sells in Europe to connect the MP5 (and their other guns) to a silencer.
    HOW-TO: Convert Umarex MP5 SD -> A5 and SBR the Umarex MP5 A5-pic4.jpg
    HOW-TO: Convert Umarex MP5 SD -> A5 and SBR the Umarex MP5 A5-pic5.jpg
    HOW-TO: Convert Umarex MP5 SD -> A5 and SBR the Umarex MP5 A5-pic3.jpg

    For option #3: Somehow you need to get your hands on the International version parts of the MP5. You need the following parts:
    578.50.06.0 Adapter for silencer, Schalldämpferadapter, 37 Euros.
    578.50.04.0 Muzzle nut, Laufmutter, 17 Euros.
    578.50.01.1 Barrel Sleeve International, Laufmantel Int. 50 Euros
    578.50.02 Barrel International, Lauf Int 150 Euros
    You only need the adapter if you plan on using a silencer, as the muzzle nut is sufficient to hold the barrel in place with the sheath.
    Unfortunately, you cannot simply call Umarex/Walther in the U.S. and order these parts. First, they most likely won’t know they exist. If you do manage to speak to somebody that knows about them, they will tell you that they do not have them and have no way of getting them—which is true. The US does not import these parts for a variety of reasons, which really sucks for us because converting the MP5 and their other products like the Uzi would be simple for us if they would do this for us, and it would make them more money. But we all can’t be smart now, can we? Somebody has to work at McDonalds, or in this case, at Umarex in management.
    If you try to get them from the German HQ of Walther, you will find a very hostile refusal. You will need to use your imagination about how to acquire them, as it is possible just tricky. You also face another issue, in particular with the barrel, and that is under German law a barrel cannot be exported easily, it is the equivalent of our lower receiver on an AR15—the restricted/serialized part.

    Only option #1 has any work involved, for the other options and when you complete the work below, if you are also in the process of converting from an SD->A5, go back up to the top instructions and pickup where you left off at step #10. Otherwise, if you are just converting to an SBR, I’m sure you can figure out how to take the barrel/sheath out and install again by following the schematics, but feel free to PM me if you have any troubles.

    As mentioned, the only work is cutting down the sheath/sleeve and then boring out the "muzzle" end for approximately 2mm. Cutting it down is easy, and a pipe cutter is perfect for this but a saw will work perfectly as well, just ensure a perfectly straight cut. The new length should be somewhere between 184mm and 182.5mm, with 184mm matching the same dimensions as the original sheath to the original barrel. Making it shorter will provide for a tighter fit and the barrel will screw in further to the adapter, which leaves less threads exposed to .22LR bullets flying out, less carbon fouling, etc.
    The tricky part to do on your own is the boring, unless you are skilled and have access to an abundance of different tools. It is a lot harder than it sounds and my personal first attempt looked horrible, but on my 2nd attempt it was pretty good (I had extra sheaths due to converting an Uzi as well). The problem is once you've cut down the sheath to the proper length the new "muzzle end" of the sheath will not have the proper end on it necessary to accept the adapter (or compensator) which “snugs” into it with the lip. Look at the end of the sheath where it originally butted against the compensator. You need to mimic that. If you look at your adapter you can see the lip and how it interfaces with the sheath. This interface is *crucial* as it keeps the barrel concentric and aligned in the entire gun/sheath. If you use the sheath without the lip, the adapter will not hold the barrel and sheath in perfect alignment, which will result in erratic accuracy and shifting parts.
    Unfortunately since the sheath is very thin already, it is very easy to break a hole in it or make it uneven, either of which will make it unusable. Also, if it looks horrible you will see that as well. So however you are going to do this, you need to have the cut down sheath mimic the end of the sheath in its original form. Given my lack of a drill press, I ended up using a Dremel in both attempts. In my second attempt, which turned out beautiful, I found a grinding bit that was the perfect size and just managed to hold the Dremel steady while widening the hole. During my first attempt I had a smaller drill bit and did not hold the Dremel securely enough, both of which resulted in a less than optimal cut down sheath/sleeve.

    Please feel free to ask me any questions. I also have a variety of other possibly useful items I can share if you will find them interesting or helpful: additional pictures, the schematics for all the various versions of MP5s (and Uzi)—although they do have some errors, MP5 (and Uzi) parts list for the US & International/European versions, names of good contacts at Umarex, etc.

  2. #2
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    Impressive to say the least. Thank for your precise tutorial.

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    This should be a sticky!!!


    Sent from my iPhone 4S using Tapatalk

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    Quote Originally Posted by zpat
    1. A5 Forearm 578.30.01.1
    2. Cocking lever tube 578.30.02.1
    3. Front sight assembly 578.70.20
    4. Push pin 578.30.09
    5. Lug tube 578.50.03.1
    6. O-ring 578.50.05.3
    7. A5 compensator/faux can 578.51.05
    8. Sight screw 578.70.24.1.
    This is awesome! Thanks for sharing.

    Would you mind sharing how much these parts cost?

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    Quote Originally Posted by TooSixy View Post
    This is awesome! Thanks for sharing.

    Would you mind sharing how much these parts cost?
    Wouldn't you know it that I have all my receipts from Walther except this one. But I do know that the entire order cost $91.88, which included everything except the sight screw and the faux can. The sight screw is one of the parts that those kind souls do not acknowledge even exists, so as of now you can't get them from Umarex but that should change soon. I ended up using my own, and you can too, just get the hole size on the back of the sight assembly and get a screw that fits that is about 1/2" long or so. I know I wrote the specs of it down somewhere and when I find it I'll edit the instructions with that. When Walter/Umarex do sell it eventually, it will cost probably $4.00 like all of their other screws do. And the faux silencer is $50 new from Umarex; however, there are a lot of people on here that have done the SBR and don't need it anymore; I'd imagine you should be able to get a used one in great condition for $25 shipped, or at least that is the offer range I was receiving when I asked people to sell me one.

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    BTW: If anyone owns an Umarex/Walther Uzi .22LR, I'm writing up something similar for that gun and I'll post it over at Uzitalk.com. FWIW, Walther did an even better job with the Uzi than the MP5. It is quite heavy, very nice feel and makes an awesome SBR (the rifle version that is). Side by side with my real Uzi you can not tell a difference other than the markings and the grip safety they used plastic instead of metal, other than that they are very nearly identical externally.

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    So the length you cut the sheath, is that to work with the 416 pistol barrel?

    I'm really leaning toward option 2 with mine. I'd like to cut the sheath right at or just back from the front of the fake 3-lug, have the barrel cut just a bit longer and use the HKParts adapter to mimic an N-style barrel.

  9. #8
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    Also, for the Form 1, who do I put down as the mfg? HK? Walther? Umarex as the importer?

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    Quote Originally Posted by ryknoll3 View Post
    Also, for the Form 1, who do I put down as the mfg? HK? Walther? Umarex as the importer?
    I put Walther and the form came back with an error note saying i should have put HK as the manufacturer.

    I left it as Walther and sent it back with a letter (I was nice about it) saying that they were mistaken and HK is NOT the manufacturer of this rifle.

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    Zpat,
    Looking forward to your post on uzitalk.

    Did you have to get your barrel cut down or does the uzi pistol barrel work?

    As far as SBRing the MP5... when i cut the sleeve i measured the original barrel, then the 416 barrel and cut the sleeve by the difference between the two measurements.

    It was close but i was able to get my fake tri-lug on and screw my silencerco adapter all the way tight.

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