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In the spring of 2017, Heckler & Koch presented the modular HK433 assault rifle family in caliber 5.56 mm x 45 NATO for the first time. Since then there have been some further developments, including variants in other calibers.
The design-determining idea for the HK433 was to create a modular, functionally reliable, precise and intuitive to use assault rifle family. According to Heckler & Koch, “above all, the operational experience from the conflicts of the last 20 years, including Afghanistan, Iraq and other places, should flow into the design of the weapon.
The HK433 combines the strengths and outstanding features of the G36 and HK416 assault rifles.” Depending on the tube length used and the use of the shoulder rest, the HK433 has an overall length of between a minimum of 577 and a maximum of 976 millimeters and an unladen weight of 3,400 to 3,600 grams. This makes it about the same weight as the G36, but significantly more adaptable to body stature and equipment. Functional and design features The HK433 works as an indirect gas pressure charger with a short-stroke gas piston system and a locked, shape-optimized rotary head lock. With this, the Oberndorfer designers relied on the reliable functional principle that is also used in the G36 or the HK416/417 assault rifle families - but this time without the impulse transmission rod.
The HK433 is available in the colors black, sniper gray and flat dark earth, the housing has an infrared absorbing coating. The housing is made from an aluminum extruded profile. This enables economical production. There is a continuous STANAG 4694 rail on the top. The handguard, which is keyed to the case top, features M-Lok interfaces at the three and nine o'clock positions (HKey interfaces are optional) and a MIL-STD 1913 rail at the six o'clock position. The weapon can be disassembled without tools into the upper part of the receiver with barrel, handguard, shoulder rest, recoil spring, bolt assembly with integrated guide rod, lower part of the receiver with grip and trigger box, and magazine. The retaining bolts cannot be lost.
Customizable operating philosophy An outstanding feature of the HK433 is the adaptable operating philosophy, which results from the architecture of the upper and lower part of the housing. The lower part of the housing includes a magazine well and a grip with an integrated trigger box. By using different housing bases, the HK433 can be converted from push button to paddle in terms of operating philosophy. The operation is based either on AR or HK416/417 systems (push button) or on weapons such as G3, MP5 and G36 (paddle). With both concepts, the weapon can be operated completely from both sides and is suitable for both right- and left-handed shooters. It should also be noted that the designers did not leave the slide catch in the trigger guard as in the G36, but positioned it outside in the form of a paddle. Optionally, the slide catch can also be mechanically deactivated on the lower part of the receiver with paddle operation, so that the weapon closes again after the magazine filling has been fired.
HK437, above with 9" tube and push-button operating concept, below with 7" tube and paddle operating concept as well as mounted helmet shoulder rest (Photo: Jan-P. Weisswange)
The grip can be individually adapted to the shooting hand using the adapter plates known from the HK pistols P30 or the SFP9. There is also a small storage compartment in the handle. Thanks to the trigger box, it is easy to set up individual trigger groups or match triggers.
Pipe structure, intake and tool-free adjustable gas extraction for normal and silencer operation are based on the HK416. The cold forged tubes are available in 11”, 14.5” and 16.5” (280mm/368mm/420mm) lengths. They can be easily changed at the user or maintenance level. A front sight holder and a bayonet mount are optional. The interface on the upper part of the housing is standard, in order to be able to attach a 40 mm grenade launcher. The recoil spring construction is similar to that of the G36, allowing a folding buttstock to be fitted. This brings advantages in cramped environments. The length and height adjustable buttstock can be folded to the right side of the weapon. The weapon remains ready to fire. Furthermore, the tactical helmet shoulder rest known from the G36C can be mounted on the HK433, which enables shooting with the ballistic protective visor closed.
The non-moving charging lever is reminiscent of the handling of the G3 or the MP5. It can be moved to the other side of the weapon without tools. It also serves as a closing aid. Markings on the ejection window indicate the position required for checking the cartridge chamber (Chamber Check) for returning the bolt. The HK433 can be secured in all charging states. Security in the secured and unsecured state and projectile forwarding capability - both in accordance with the NATO AC225/D14 specification - are just as much a part of the security features as over-the-beach capability. The HK433 accepts the in-house HK Gen3 PM plastic magazines, but can also use other AR-compatible cartridge cases.
HK437 sneaker – the sister in 300 BLK The HK433 family was the first to expand with a sister in .300 Blackout (7.62mm x 35, .300BLK for short). This variant is called HK437. To explain: The HK code used since the company was founded categorizes the weapons developed and produced by Heckler & Koch by generation, type of weapon and calibre. The 7 stands for special caliber, which also includes .300BLK. The name "sneaker" refers to the purpose for which the weapon was developed: silent operations as a sneaker or sneak.
Size comparison MP5SD (above) and HK437 with 9" barrel (Photo: Jan-P. Weisswange)
The HK437 has basically the same body as the HK433, but the throttle pickup is located a little further back. It also has a modified HK433 breech, a new barrel with a length of 9" or 7" (229 mm/178 mm). There is also a separate magazine, which is optimally designed for .300 BLK. The gas adjustment ensures that the HK437 can use both supersonic and subsonic ammunition reliably in automatic mode - if necessary from a magazine and in the ammunition-typical ideal case even without adjusting the gas intake. The people from Oberndorf demonstrated this during a visit to the ES&T shooting range. Heckler & Koch sees the HK437 as a possible replacement for the MP5 and the silenced MP5SD, especially in the 9 mm x 19 range. With a compact Rotex silencer and a 9" pipe, the HK437 has almost identical dimensions to the MP5 SD. However, it achieves a significantly higher effect. The MP5SD slows down the supersonic load DM41 to 285 m/s and gives it a muzzle energy of 380 joules. In contrast, a .300 BLK subsonic load with a bullet weight of 220 grains from the compact assault rifle with a 9" barrel travels around 320 m/s and, at around 742 joules, achieves more than double the muzzle energy. Another consideration: at 320 m/s, the .300BLK subsonic ammunition stays under the speed of 9mm x 19 supersonic rounds, which reach around 400 m/s from submachine guns such as the MP5. This means that such subsonic loads could also be considered for use on shooting ranges that are only approved for 9 mm x 19.
Shooting with the HK437 with a 7" barrel (Photo: Jan-P. Weisswange)
outlook The HK433 was one of three candidate weapons for the new "Bundeswehr Assault Rifle" system. It is known from the tests that all three weapons presented met the selection criteria and were technically close to each other. That certainly makes the new family of weapons interesting in the markets that can be reached.
Precision shooting with the HK433 in 16.5" barrel length (Photo: Jan-P. Weisswange)
Heckler & Koch now sees variants of the 433 series in the larger NATO caliber 7.62mm x 51 as well as for the Kalashnikov cartridge 7.62 mm x 39 as the next steps in the family expansion. Both versions are in the form of the HK231 and the HK132 already in development. The HK231 in 7.62 NATO picks up on the trend towards what Heckler & Koch calls "two-track armament": the weapon mix of 5.56 NATO and 7.62 NATO. ES&T has already been able to take a look at a prototype of the HK231. The weapon will be available with barrel lengths of 13", 16" and 20". In addition, it will use its own HK Gen3 PM, but will also be compatible with Magpul magazines for the DPMS interface. With the approach of a 7.62 Kalashnikov variant, Heckler & Koch takes two developments into account. In the area of authorities, such a compact assault rifle would create “equality of arms” with a terrorist attacker who was acting militarily and was equipped. In the armed forces sector, the main customers to be considered are special forces operating behind enemy lines. On the one hand, these could use ammunition available in the theater of operations and, on the other hand, they would not leave any telltale shells behind.
The new weapon family HK433 should be available on the market from this year. Jan Philipp Weisswange
After viewing and reading materials I've found and come into, I do have some info and thoughts on the 433 family.
One notable mechanical element about the 433 is that it does have a recoil buffer built into the recoil spring assembly. This seems to be HK's attempt to improve upon one of the best things about the G36, which is its soft recoil and control-ability in rapid semi auto fire and full auto. Also probably avoids the use of a muzzle brake or compensator, which is undesirable in the shorter barreled variants. The recoil buffer will probably be of good use in the 7.62mm NATO 231.
IMO, compared to other handguards, even the MLok handguard on the 433 family seems to be very slim and lightweight. It seems doing the fashionable C-clamp grip is pretty easy. Also reinforces how narrow the front of the upper of the 433 is (the G36 is similarly as slim).
Also, as noted above (post #920 in HKPro's HK433 thread), it does seem like though it unavoidably will be a bit heavier due to the 7.62mm NATO's larger powder charge (M855A1 type ammo runs similar chamber pressures), dimensionally it shouldn't be much larger. Doubtlessly, we'll learn more when HK launch the 231 (I suppose it could be possible between now and Eurosatory in June?), and all we have now is a side profile sketch, but it could possibly be telling. If HK run the reported 13" 16" and 20" barrel lengths, it'll be the same length as the 433 with the 13.5" (not featured), 16.5" (standard) and 20.5" (not featured) barrels. Or if it goes for the 13.5", 16.5" and 20" barrels, it'll only be half an inch longer than the 433 if using those barrel lengths. Obviously, this accounts for the fact that the 5.56mm NATO/.233 Rem. is about 1/2 an inch shorter in OAL than 7.62mm NATO/.308 Win.
Also as noted in Tspeis' post above (post #920 on the HKPro 433 thead), this can open up stuff on the caliber end for rounds that are compatible with the OAL and base/rim diameter similar to or smaller than 7.62mm NATO/.308. Such as the mentioned 8.6mm Blackout for SBRs and stuff like 6.5mm Creedmoor, .260 Rem (.308 Win/7.62mm NATO necked down for a 6.5mm bullet), and 6.8 True Velocity (loaded to the same chamber pressures at 7.62mm/.308), and, maybe 6.8mm/.277 Sig Fury (chamber pressure may be an issue, though it's obvious that HK have been paying attention to trends).
It should also be noted at the same time that HK are working on a lightweight 7.62mm belt fed LMG known as the HK421, which may be in the same train of thought as the 7.62mm FN Evolys. Not to mention that HK have been suggested as working on lightweight versions of the MG4 and maybe MG5.
And I've read that Germany is re-racking the aborted G26 DMR program. The German Army aborted it because none of the rifles really met requirements at the time and it was a low priority RFP. However, between recent events and new interest in the program, it's being restarted. And HK may have 1-2 new entries for it if it comes to fruition. The HK231 is maybe obvious if it's ready, but HK did also release a photo of the M110A1 that's not a full US Army spec M110A1 (it seemed it was on a G28 or 417 lower and had a B&T suppressor instead of the OSS suppressor). Maybe one or both could be a G26 candidate.
From a discussion at HKPro, it now seems that it's possible (though unconfirmed) that the 433 and 231 might, if not share upper, use a virtually identical design. It was something that HK asked of one of the guys there who works for a law enforcement agency or a distributor of such items, and he suggested a 5.56mm and a 7.62mm rifle that is basically the same size dimensionaly.
Also, someone has done analysis on a 433 photo and 231 illustration from the German language 433 guide that suggests that the uppers for the 433 and 231 are the same size (grips and trigger guards match up, same number of rail sections on the upper's top pic rail).
I only have the English language guide from Teufelshund Tactical, and I tried to post it as an attachment, but I got a message that it's too big to be processed. If anyone can post it here, I'd appreciated it.
Seeing the Teufelshund Tactical video, I noticed that the bolt seems to be spring loaded--it rebounded back to the extended position after James pushed the bolt. Is there a purpose to have the bolt spring loaded like that?
Also speaking of that, I re-read the Brochure this morning, and it seems that HK are maybe pushing the multi-caliber thing. They do emphasize the amount of parts interchangeable between the 433/437/231, and talk about how the different caliber lowers can interchange. Also seems to suggest (as previously hinted at) that the 433/437/231 may share the same basic upper.
Amazing brochure, thank you…
Now I HATE HK….. not to be confused with HK’s.
I find it at unholy act to have stuff like this but ”we” American civilians, are considered the enemy and are denied access to this stuff.
I don’t care if it’s the German Government, HK Germany should be using their clout to overcome these obstacles.
MAN JUST EFF IT!!!! I’m moving on to High Points…. At least I’ll have more money for ammunition and maybe able to eat!
Well that’s my early more rant.
thanks for sharing that brochure @Barn Owl Lover it was extremely informative…. Especially since it was in English!!!!