I now have 4 complete RepRap'ed Milestag guns. The only problem is that I only have two optical sights available and my son and his friends were complaining about aiming the two sightless guns.
So I designed and printed some classic style iron sights. These are not ideal for the kids as they take a bit of effort to use but they are better than nothing.
Here is the sight after printing:
And attached to a Mk3 Milestag gun:
I've been letting my son use them as he and his friends are an excellent test of robustness, the only casualty so far was a sight mount that I have since reprinted at 100% fill. Here they are all tooled up with Mk1, Mk2 and Mk3 guns. All gun bodies are entirely 3D printed except for barrels (20mm conduit) and the optical sights.