Receivers / Flats / Uppers
Explore our premier selection of HK receivers, flats, and uppers at HKParts, perfect for building or upgrading your Heckler & Koch firearms. Our products feature precision-engineered MP5 receiver flats, HK 416 complete upper assemblies, and a wide range of custom options designed for tactical and precision shooting. Whether you are customizing an MP5, upgrading an HK416, or constructing a new firearm, our high-quality components provide unparalleled reliability and performance.
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HK416, HK417, MR556, MR762 Bridge
H&K Heckler & Koch
$24.95H&K HK 416/417/MR556/MR762 Bridge For Lowers Compatible With: HK MR556 HK 416 HK MR762 HK 417HKP-02676$24.95 -
MR556 A4 Upper Receiver Kit - 16.5″ - 5.56 - M-LOK
H&K Heckler & Koch
$1,939.00H&K MR556 A4 16.5″ 5.56 M-LOK Upper Receiver Kit This kit includes a complete upper receiver/barrel assembly, allowing Mil-Spec 5.56mm AR-style rifles to be retrofitted to HK’s piston and pusher rod system. This system utilizes a piston...HKP-21909$1,939.00 -
HK MP5K, SP89, SP5K Trunnion - 9mm - RS
RCM
$69.95MP5K Reverse Stretch Trunnion US-made to exact factory HK specifications for the HK MP5K, SP89 9mm builds. There is a difference between the MP5K and the MP5 trunnion. This offering is the correct trunnion for the MP5K and all MP5K PDW variants,...HKP-02242$69.95 -
HK21, FMP21 Teardrop Rail Set - T-Rail
HKP HK Parts
$197.95HKP HK21/FMP21 Teardrop Rail Set HK teardrop style reinforcement rails. The ultimate choice for period correct builds. Expertly crafted in the USA from high-quality 4140 steel, these ready-to-weld rails are engineered for precision and durability...HKP-21671$197.95 -
MP5K Complete Weldment Set
$59.95MP5K Complete Weldment Set Each set of weldments is all of the weldments required for an MP5K flat. Includes: Rear sight base Sight tab Case deflector Semi auto shelf Side reinforcement tabs 2 X rear stock bushingsHKP-16231$59.95 -
HK93 Trunnion
RCM
$65.00RCM HK93 Trunnion Made to exact factory HK specifications for the HK93, HK33 type builds. These are the best trunnions of their kind on the market. Machined to HK spec making the install painless and hassle free. The way a custom HK build it should...HKP-20807$65.00 -
HK G36, SL8 Cocking Handle Axle Pin
H&K Heckler & Koch
$11.95HK German G36 & SL8 Cocking Handle Axle Pin This is the rivet pin that is used to attach the swiveling cocking handle to the body of the carrier. These can be replaced as they break and wear. Compatible With: HK G36 HK SL8HKP-01877$11.95 -
HK MR556 A4 Upper Receiver Kit - 11"- M-LOK
H&K Heckler & Koch
$1,998.95H&K Heckler & Koch MR556 Upper Receiver Kit A4 -11″ - M-LOK This kit includes a complete upper receiver/barrel assembly, allowing Mil-Spec 5.56mm AR-style rifles to be retrofitted to HK’s piston and pusher rod system. This...HKP-21910$1,998.95 -
Out Of Stock
MR556 Upper Receiver Kit -16.5" - M-LOK
H&K Heckler & Koch
$1,779.95New HK Factory German MR556 Upper Kit with M-LOK forearm Includes: Complete MR556 upper receiver with M-LOK forearm MR556 Bolt group Complete Tungsten Filled HK Buffer HK Buffer Spring One 30 Round HK Steel Maritime Magazine No FFL required as the...HKP-17366$1,779.95 -
HK417, MR762 Castle Receiver Extension Nut for Buffer Tube
H&K Heckler & Koch
$44.95H&K HK MR762/417 Castle Receiver Extension Nut For Buffer Tube - Black New HK German manufacture and the factory correct offering with the proper installation screws and staking guides. Compatible With: HK MR762 HK 417HKP-16768$44.95 -
Out Of Stock
HK G36 Backplate with Recoil Buffer - US
USA
$44.95HK G36 Backplate With Recoil Buffer New G36 Backplate with new G36/SL8 recoil buffer. This is a great spare or replacement to have on hand. These are also required for those that are doing the SL8-G36 conversions provided by Tommy Bostic & Chopstix...HKP-18538$44.95 -
HK G36, SL8 Cocking Handle Axle Pin - USA
USA
$10.95HK G36, SL8 Cocking Handle Axle Pin - US Made This is the rivet pin that is used to attach the swiveling cocking handle to the body of the carrier. These can be replaced as they break and wear. Compatible With: HK G36 models HK SL8 modelsHKP-18367$10.95