Mil-Spec Parts:
The only elements that are mil-spec are the buffer tube and the Picatinny 1913 rails. You may add any stock that is mil-spec on to the buffer tube.
The 1913 rails accepts any 1913 accessories from lasers, grips, lights and anything else you might choose to mount.
Buffer Tube:
The Buffer Tube is "near mil-spec". What do I mean by this? I measured the outer diameter of the HK's buffer tube and it is about 1/32 of an inch smaller than a true mil-spec M4 mil-spec buffer tube.
The slight size difference results in mil-spec stocks like the Magpul CTR being slightly loose. Not terrible but the CTR is suppose to be able to clamp tight onto the buffer tube to remove any play. Well, the HK's stock is just a little bit too small and there is still a rattle. Save yourself some money if you put a Magpul stock on and get the MOE. Both the CTR/MOE stocks will have play. So why spend the extra $50 for the CTR?
The Fake Stuff:
Forward Assist: The HK also sports a few "fake" parts such as the forward assist (cosmetic / non-functional). You can push on the forward assist but it does not move the bolt forward.
Bolt Release: The bolt release is cosmetic and does nothing. This is a bummer since the bolt on the HK will hold open on the last round shot. To get the bolt to release after reloading, you have to pull back on the charging handle. This is not as convienient as pressing the ping pong paddle to slam the bolt shut.
Mag Catch: The mag catch is also custom to the UMAREX rifle. The magazine has a custom follower which WILL NOT ACCEPT any Blackdog/Ciener/CMMG 22lr magazine. It will only work with the HK/Colt UMAREX magazines.
Forward Assist: The HK also sports a few "fake" parts such as the forward assist (cosmetic / non-functional). You can push on the forward assist but it does not move the bolt forward.
Bolt Release: The bolt release is cosmetic and does nothing. This is a bummer since the bolt on the HK will hold open on the last round shot. To get the bolt to release after reloading, you have to pull back on the charging handle. This is not as convienient as pressing the ping pong paddle to slam the bolt shut.
Mag Catch: The mag catch is also custom to the UMAREX rifle. The magazine has a custom follower which WILL NOT ACCEPT any Blackdog/Ciener/CMMG 22lr magazine. It will only work with the HK/Colt UMAREX magazines.