HK21 Receiver Box
INTEGRAL REINFORCING RAILS
For those of you who are using factory sheet metal keep in mind if you simply weld half rails to the weapon receiver to the rear of your sheet metal you have no reinforcing where you need it most...under the sheet metal. The reason the factory beefs up this area is readily apparent when you get an out of battery round and bow out your receiver just back of the trunion. We have repaired even factory type 21's that this has happened to...you can only imagine the damage with no reinforcing.
Enough said!! We don't want to paranoid you just inform you so you can have a HK21 worth shooting for a long time.
Also you might notice you'll have to have the semi auto style ledge welded on to use semi groups or registered full-auto groups and sears.
PERFECT ALIGNMENT OF THE RDTS RECEIVER BOX IS ACHIEVED IN ALL
The trigger group ledge is already installed on the rear. No need to weld one on and hope it is position right so your sear release lever will have proper timing.
The RDTS RECEIVER BOX is already machined for minimal custom fitting. The factory sheet metal is far from being ready to accept any of its parts. The feed box locking pin holes are undersized and the sheet metal lips on both left and right sides have none of the cuts and relief's needed to accept to feed tray. Without another HK21 to reference to you'll have many hours of fitting in store.
We have also reinforced the rear of the left side of the RDTS RECEIVER BOX. On the factory sheet metal there is an additional cast part welded in to attach the lower portion to the radiused upper sheet metal. Look at the photos and you'll see what we are talking about!
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RDTS MANUFACTURING INC.