Sure, you've asked yourself - whay the greatest warriors of humanity, describet as giants, are similar to ordinary human in scale. That's why guides about re-scailing space marines are so popular. Today you'll se one, made by Ivan Prokunin. Of course, you won't change all your army this way, but for several models in diorama or a guy for painting competition...why not?
Before making the chest wider you'll need to carefully cut it apart. Separate all sticking out parts and the belt to make it easier.
You can use frames or just a sheet of plastic for the fillers. This photo shows how it can be done with plastic...
And this - with the frames. The plastic concept obviosly looks beter.
Next - let's lengthen the legs. Better put pins inside - the construction might easily break. You can also make new knee pads to match the scale.
A huge spacemarines drawback - is lack of stomach. You'll have to sculpt it from Green Stuff.
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For more realictic look just add grenades, bags and pistol. You cal also add some battle damage. The photo shows the comparisson with normal human and with the original model.
Playing such models on empty table is a sin. So, start creating your own amazing table right here