All factory 23E's only came with 1000m rear sights.
I think the Gen 3 that you and I have was std.
Most that were ordered must have opted for the Gen 4
1000m upgrade which makes these rarer.
The 8 NIB 23E's I have/had only had Gen 4's.
I am interested in creating a precise model of HK21E, I have allready found several parts available online but I could really use some help from owners of one with taking measurements of some parts that are unique to this exact platform, I can send a picture on which are shown the lengths that interest me either here or via PM or email... well, not sure about PMs though since this function seems to be restricted for new users
hk21man since he has detailed blue prints, part by part. You may only be looking for basic measurements, but if what you are looking for is very detailed, not sure how much he would be willing to share, most builders have invested countless hours to create this data, to just give it away.
I remember member Aviatordave did a 3D model of HK21 feed mechanism maybe he has other stuffs.