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Posted: 3/10/2019 2:46:29 AM EDT
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ETA: With GP switching importers and now the inevitable arrival of the A3, the following modification is probably moot. I finished it a few weeks ago thinking I would never see an A3 in the near future and began writing this before GP's announcement last week. That said, the following is how I modified my Stribog from A1 to A3 to include folding stock and Geissele trigger mods... The biggest thing initially holding me back from buying a Stribog was the straight blowback action. After playing around with CMMG's Guard, I got spoiled with delayed blowback. Once I discovered the A3 version existed, I decided to wait only to have Eagle Imports say they "had no plans to import it anytime soon".  Although I had no desire for another straight blowback, I bought one anyway. I tried it out and while a little snappy, was nothing worse than some 9mm AR's I've handled.
I started researching the A3, collecting info & pics from the internet. From what I gathered, the A1 and A3 were the same except for a few components which looked to be interchangeable. I put emails out to Eagle, GP Canada, GP Slovakia, etc, all asking on availability of A3 parts. And all said no. But I did get an explanation as to why; essentially had to do with licensing, import rules, etc. So much for an A3 conversion. But a modification on the other hand... I studied the pics I had, drew up the delayed action parts in CAD, made sure my measurements were good, bought some spare parts from Eagle, then headed to my shop. Step 1, "Roller": Easiest part to make. Best guess, the A3's roller is 5-6mm OD. I decided to use 0.250" since all my tooling/collets are standard. Ordered a 0.250" HSS drill blank and cut to size. 
Step 2, Charging Block: Milled slot for the roller, shortened to size, profiled sides like A3 (reduces weight), and bored out existing 10mm hole to 0.4375" (did this to allow use of different pistol action springs; 1911, Glock, Sig, etc, with spring rates from 11# up to 24#) 
Step 3, Trunion. Used a ball nose endmill to cut the recesses, then smoothed down the rear edges: 
Step 4, Locking Piece: Hardest part to make. Several 1/8" endmills gave their life in the replication of this part. 11.1mm (0.4370") HSS drill blank with a 40* angle cut (used 40* since 80* locking piece is very common in the MP5). Took some left over charging block, milled it down. Positioned rod into block, drilled two 0.125" holes for retaining pins to hold them together. (I believe GP does this to allow use of the same locking rod with different weighted blocks for longer barrels, etc). Discoloration is grease: 
Step 5, Buffer Plate: Milled out existing spot weld, removed guide rod, replaced with shorter 0.250" rod. (in hindsight I should've just shortened the exiting guide rod since it's not much smaller at 0.236" OD) 
Step 6, Action Spring: I ordered several to try. Only one that really fit (i.e, long enough) was from a full size Sig P320. I got the green spring (40/45/357) but also ordered a red spring (9mm) to try. Original Stribog (top), P320 green (middle), P320 red (bottom) 
Step 7, Charging Handle "Shuttle": No clue what this piece is actually called. Scratch made from Nylon 6/6. "Legs" are bowed slightly to prevent it free floating in the receiver when bolt is locked back. 
All laid out with Cerakote on the bare metal: 
For comparison, still shot from YouTube showing a real A3's internals (video credit to Vins Cat): 
In case anyone's interested, here's how the roller delay works (best I understand anyway): Bolt closed. Spring pushes forward against locking piece, forcing roller down and "locking" it into trunion's recesses: 
Cartridge ignites. Reward motion forces the roller out of the trunion which pushes the locking piece reward against inertia and spring tension: 
Once roller is clear of trunion, the bolt is free to cycle as normal (roller is now riding on inside edges of receiver):  Stock: Started with Scorpion EVO folding brace & adapter and modified it to fit onto factory Stribog backplate: 
Looks good but Form 1 came back waaay sooner than expected. So bye bye brace, hello stock. Tried UMP. Too long: 
Tried the B&T, just right: 
Trigger: Nothing wrong with factory trigger, just wanted something different, plus it provides three 922r parts. With a few shim washers and slightly opened-up trigger hole, a standard AR hammer/trigger fit perfectly. Had a Geissele SD3G laying around so why not: 
So does it work?? I shot 200+ rounds and had zero issues with the gun itself. It 'feels' softer than what I remember but would love to shoot it side by side with an unmodified gun to see if there's any substantial difference. All in all, I'm happy with the end result. |
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Thanks all.
I literally finished it about a week and a half before GP announced their new partnership with Global Ordnance, future import of the A3, etc. I'm still planning on buying one when they finally do hit the shelves as I'm curious just how close I got with this thing! |
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How does the trunnion connect to the gun itself? Do you have a photo of that? The guts (L-R): The barrel goes through a rear support 'plate' (also holds the bolt catch retention spring), the rear trunion, the front trunion, then a front support plate. All held together with two barrel nuts (yep, there's two): 
I made this wrench to remove the nuts: 
With the two nuts removed, the barrel will slide out of the rear of the receiver with a slight tap of a mallet. Of note, the ejector also needs removal to allow the barrel to slide completely out. With the barrel gone, the front & rear trunions can be pulled from the receiver. The two support plates will also come out pretty easily: 
Here's what it all looks like assembled in the gun: 
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Quoted:
Holy Damn, incredible! Quoted:
Holy Damn, incredible! Quoted:
Impressive! Wow! Awesome work. Quoted:
You sir are extremely talented. Hats off. This so called "hobby" of mine has turned into full blown obsession... 
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Got the modified tri-lug adapter in from TROS and mounted up; very pleased how it turned out: https://i.imgur.com/Up2wxT8l.jpg https://i.imgur.com/g4uJpD1l.jpg https://i.imgur.com/Ifh6iZgl.jpg https://i.imgur.com/nZUo4qGl.jpg Stribog in it's current and final form. I dig it, for now I can cross this project off the board: https://i.imgur.com/PoqnfO2l.jpg |
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Maybe give us a taste here?  |
| Question for the OP. Is the barrel nut ID larger than the tri lug diameter? It looks larger in the pic but not sure and also not sure how you re-assembled but it looks as though you assembled with the tri lug installed. Just wondering if it is possible to produce a barrel with an integral 3 lug. |
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Question for the OP. Is the barrel nut ID larger than the tri lug diameter? It looks larger in the pic but not sure and also not sure how you re-assembled but it looks as though you assembled with the tri lug installed. Just wondering if it is possible to produce a barrel with an integral 3 lug.
Nevertheless, it does in fact fit. It's tight and just needs to be taken slowly. FWIW, the adapters I used are ILWT and TROS. Both excellent quality and have no doubt they are as close to HK-spec as it gets. |
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Barely. The barrel nut ID is ~0.750" (19mm). Hard to accurately measure the lug OD but according a diagram I have, it's supposed to be 0.824"?
Nevertheless, it does in fact fit. It's tight and just needs to be taken slowly. FWIW, the adapters I used are ILWT and TROS. Both excellent quality and have no doubt they are as close to HK-spec as it gets. Quoted:
Quoted:
Question for the OP. Is the barrel nut ID larger than the tri lug diameter? It looks larger in the pic but not sure and also not sure how you re-assembled but it looks as though you assembled with the tri lug installed. Just wondering if it is possible to produce a barrel with an integral 3 lug.
Nevertheless, it does in fact fit. It's tight and just needs to be taken slowly. FWIW, the adapters I used are ILWT and TROS. Both excellent quality and have no doubt they are as close to HK-spec as it gets. |
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Yeah that'd be awesome. Rob & Mark are both good dudes and hope they do. I contacted Rob awhile back about a different tri-lug barrel and he was too busy with the MPX stuff. But if Stribog does take off in popularity then hopefully the aftermarket follows.
Now that I think about it, I could've sworn I've seen pics of a Grand Power factory tri-lug. Hopefully it gets imported but different barrel lengths are always nice too! |
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Now that I think about it, I could've sworn I've seen pics of a Grand Power factory tri-lug. Attached File 
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I’m a huge fan of the Stribog and love mine... but I do not like that factory stock, sure it completes the look but the B&T looks WAY better and more natural on it, maybe B&T will offer that mod if the Stribog takes off even more?
OP, how does this shoot in terms of smoothness (A3 mod) compared to MP5 and B&T? |
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I’m a huge fan of the Stribog and love mine... but I do not like that factory stock, sure it completes the look but the B&T looks WAY better and more natural on it, maybe B&T will offer that mod if the Stribog takes off even more? OP, how does this shoot in terms of smoothness (A3 mod) compared to MP5 and B&T? As far as smoothness, I'd say it's up there with an MP5 but not quite as soft. However, my experience is with an MP5A2 with a lot of 'duty' accessories on it (light, laser, optic, etc). That additional weight probably plays a part. I've never tried say, a clean MP5K, so that might be a different story. No clue about B&T. My buddy just ordered an APC9 so I'm sure I'll get to see it soon. I'm fascinated by it's hydraulic recoil buffer. Going to a big shoot this weekend so hopefully I'll get to try some different guns side by side and have more data for comparison. |
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Looking forward to the results!
If GO and GP bring in the A3 and it’s as smooth as the more expensive competitors I can see it definitely carving out a fair share of the market, that and steel reinforced feed lip mags on the way make it a no brainer All this being said I’d love a GHM9 or APC9 pro |
Had an opportunity to go to a shoot today with lots of machine guns; everything from auto pistols to M60s. Pure awesome. But the highlight was shooting my "A3" Stribog against what I consider gold standards in SMGs: MP5K-PDW, MP5A3, and MP5SD (SD was on another table just off camera):
The results? MP5K-PDW - Snappier and not as soft as Stribog. They have similar lengths of bolt travel but Stribog has +2" of barrel. Interestingly, they had almost identical setups with stock and VFG: 
MP5A3 - Was excited to finally try a slick MP5 without any bells & whistles. It had a slight edge over Stribog and I do mean slight. It was a touch softer but barely. I only noticed because I shot them back-to-back. Had I shot them an hour apart I would've called it a draw. MP5SD - Yeah no real contest here but then again they're two completely different guns. The SD is ridiculously smooth. And quiet. And expensive. If Stribog were integrally suppressed with a big 'ol can, weighed 25% more, etc, I'm sure it would hold it's own against the holy grail of SMGs. (of note, the SD was super gassy, much more than expected. I had to stop a few times to rub my eyes.  )
Conclusion/Prediction - The A1 to A3 modification has made this my favorite gun in the safe, hands down. It's amazing to shoot. When the actual A3 becomes available, it'll be a game changer in the PCC world. |
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Had an opportunity to go to a shoot today with lots of machine guns; everything from auto pistols to M60s. Pure awesome. But the highlight was shooting my "A3" Stribog against what I consider gold standards in SMGs: MP5K-PDW, MP5A3, and MP5SD (SD was on another table just off camera): https://i.imgur.com/nUvPQYQl.jpg?1 The results? MP5K-PDW - Snappier and not as soft as Stribog. They have similar lengths of bolt travel but Stribog has +2" of barrel. Interestingly, they had almost identical setups with stock and VFG: https://i.imgur.com/grv8xBZl.jpg?1 MP5A3 - Was excited to finally try a slick MP5 without any bells & whistles. It had a slight edge over Stribog and I do mean slight. It was a touch softer but barely. I only noticed because I shot them back-to-back. Had I shot them an hour apart I would've called it a draw. MP5SD - Yeah no real contest here but then again they're two completely different guns. The SD is ridiculously smooth. And quiet. And expensive. If Stribog were integrally suppressed with a big 'ol can, weighed 25% more, etc, I'm sure it would hold it's own against the holy grail of SMGs. (of note, the SD was super gassy, much more than expected. I had to stop a few times to rub my eyes. )
Conclusion/Prediction - The A1 to A3 modification has made this my favorite gun in the safe, hands down. It's amazing to shoot. When the actual A3 becomes available, it'll be a game changer in the PCC world. Have you suppressed it yet? |
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https://media.giphy.com/media/HjheuybfwDGnu/giphy.gif I wonder what a CZ stock/tail hook setup would look like on this. I anticipate the next thread will be you injection molding a glock lower that uses ar grips for this...
And maybe a 10mm thread after that one...  |
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60 Driver Jaroslav, the designer of the Stribog and owner of Grand Power has this to say on the Stribog Owner’s Facebook page regarding your warranty and straight up ingenuity: Quoted:
60 Driver Jaroslav, the designer of the Stribog and owner of Grand Power has this to say on the Stribog Owner’s Facebook page regarding your warranty and straight up ingenuity: Cool getting props from Jaro though, maybe now he'll send me a free sticker or something neat! ;-) Yeah I never expected to activate my warranty had something gone south. If it had, the gun was reasonable enough to not be a costly mistake. Now would I try this with an HK or B&T? Mmm, probably not. Sadly, I'm sure there're plenty of dudes who tweak their guns, blow them up, then turn to the manufacturer and say "I dunno what happened...can I have a new one please?". Reminds me of a guy in high school who ate all but the last bite of his Big Mac, magically "found" a hair in it, then returned it to the counter demanding a fresh one. Jerk. Quoted:
Have you suppressed it yet? |
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https://media.giphy.com/media/HjheuybfwDGnu/giphy.gif I wonder what a CZ stock/tail hook setup would look like on this. I anticipate the next thread will be you injection molding a glock lower that uses ar grips for this...
And maybe a 10mm thread after that one... I'm already planning to model the lower and see if I can make it for different magazines! With my luck though, Global Ordnance will start importing lowers right after I finish... |
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Quoted: CZ stock was in the running for it. I may still make an adapter to try. I think the lines would closely match the gun like the APC. I'm already planning to model the lower and see if I can make it for different magazines! With my luck though, Global Ordnance will start importing lowers right after I finish... |
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How does it compare recoil wise with a B&T GHM9? I really am liking my GHM9. It’s amazing. The price of the striborg is a huge selling point. If it runs good like I am hearing then it will be very successful. I am interested in the recoil impulse. Personally, I'd wait for the A3 version of the Stribog to be imported but the price point of the A1 is still fantastic for what you're getting. |
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Great job on the conversion. I hope Global Ordnance offers a conversion for the a1's. A limited amount of Grand Power factory side folding stocks are available on Global's website. Get them while there Hot! https://globalordnance.com/stribog-polymer-side-folding-stock-for-registered-short-barrel-stribog-rifles-upc-8588005944106/ |
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I have been in contact with Custom Smith MFG. They are going to support the stribog. To quote them, Gonna make some cool stuff for it. I am pretty stoked about this!
https://customsmithmfg.com |
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They are also making a non-reciprocating kit which looks pretty simple. Looks like a small piece of (edit 4140 alloy steel, then hardened, tempered, and finally black nitride) w/a spring loaded plunger forward the ch.
Thanks for starting this thread & sharing your work. I love my Scorpion, but see an A3 Stribog in the near future. |
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They are also making a non-reciprocating kit which looks pretty simple. Looks like a small piece of Al w/a spring loaded plunger forward the ch. Thanks for starting this thread & sharing your work. I love my Scorpion, but see an A3 Stribog in the near future. |
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Where did you see the non-reciprocating kit? Quoted:
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They are also making a non-reciprocating kit which looks pretty simple. Looks like a small piece of Al w/a spring loaded plunger forward the ch. Thanks for starting this thread & sharing your work. I love my Scorpion, but see an A3 Stribog in the near future. https://hbindustries.net/store/shop/gp-stribog-non-reciprocating-bolt-conversion/ |
| Thanks |
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Quoted:
They are also making a non-reciprocating kit which looks pretty simple. Looks like a small piece of (edit 4140 alloy steel, then hardened, tempered, and finally black nitride) w/a spring loaded plunger forward the ch. Thanks for starting this thread & sharing your work. I love my Scorpion, but see an A3 Stribog in the near future. |
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