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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HK91, G3 Trunnion - Used
H&K Heckler & Koch
$39.95HK German HK G3 & HK 91 Trunnion - Used These trunnions are from demilled G3 parts kits and will have leftover receivers and barrel stubs installed along with factory barrel pins. Please note the picture shows one with the demilled parts removed...HKP-00718$39.95 -
$19.95 -
HK 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 G36, SL8 Magazine Paddle Release
USA
$17.95US HK G36 and HK SL8 Magazine Paddle Release HK G36 Mag Release or mag catch. Compatible With: HK SL8 HK G36 HK G36K HK G36CHKP-18222$17.95 -
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 -
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 -
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 -
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 -
HK MP5K Weldment Set, Complete
$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 MR556 A4 Charging Handle - Ambi
H&K Heckler & Koch
$199.95H&K HK MR556 A4 Ambi Charging Handle Upgrade your MR556 or HK416-style rifle with this factory H&K ambidextrous charging handle, designed for smooth, reliable operation from either side. Built to Heckler & Koch’s exacting standards,...HKP-21933$199.95 -
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