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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HK MP5K Trunnion - 9mm
HKP HK Parts
$57.95HK MP5K Trunnion - USA US made to exact factory HK specifications for the HK MP5K type builds. Machined completely from ordnance grade steel and heat treated to factory specs. These are the best USA made trunnions on the market. Machined to HK spec...HKP-17964$57.95 -
AR-15 Mil-Spec Buffer Tube Kit
HKP HK Parts
$42.95Mil-Spec Buffer Tube Kit Compatible With: AR-15 style platforms Not correct length for HK rifles Includes: Made with T7 7075 aircraft-grade aluminum Made in the USA with a polished inside tube Mil-Spec triple hard coat Teflon anodized finish Each unit...HKP-02735$42.95 -
HK MP5, MP5K Rear Sight Base - Billeted
HKP HK Parts
$17.95HKP HK Parts Billeted Rear Sight Base - Weldment for HK MP5 and HK MP5K All steel HK MP5, MP5K billeted rear sight base. The most correct MP5, MP5K rear sight base available. The only billeted factory correct sight base with the factory HK German side...HKP-18087$17.95 -
HK MP5, MP5K Paddle Mag Release Contact Piece
H&K Heckler & Koch
$59.95Heckler and Koch 9mm Contact Piece for Paddle Mag Release for HK MP5 and HK MP5K - German This is the real deal NOT the .308 or .223 contact piece. Hard to find factory-correct, brand-new, latest production German HK 9mm contact piece. Compatible...HKP-00118$59.95 -
Picatinny Rail for HK Receivers - 13 Slot
DTAC Dakota Tactical
$74.95DTAC Picatinny Rail For HK Receivers - 13 Slot Mil-Spec all steel picatinny rail in the white, relief cut for HK receivers & made for mounting scopes and optics to HK builds. This unit easily welds to the top of your HK receiver. Compatible With: HK...HKP-17818$74.95 -
HK UMP, USC Lower Locking Pin
H&K Heckler & Koch
$36.95HK German UMP Lower Locking Pin For use with all HK UMP lowers and USC to UMP conversions. New HK German manufacture.HKP-00595$36.95 -
HK91, G3 Magazine Catch
H&K Heckler & Koch
$19.95Heckler and Koch Magazine Catch for HK G3 and HK91 High-quality HK German production units are brand-new. These also have the proper newer style cut in them and round shafts. Compatible With: HK91, G3 PTR91HKP-02073$19.95 -
HK416, MR556, HK417, MR762 Bridge
H&K Heckler & Koch
$24.95Heckler and Koch HK416, HK MR556, HK417, and MR762 Bridge For Lowers Compatible With: HK416, MR556 HK417, MR762HKP-02676$24.95 -
HK UMP Magazine Release Axle
H&K Heckler & Koch
$19.95Heckler and Koch Magazine Release Axle for HK UMP Replacement magazine release axle for HK UMP platforms. This component is commonly replaced due to wear or breakage and may also be required when configuring compliant magazine release systems where...HKP-02159$19.95 -
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 -
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 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