Just bring it to MS paint.
Right click and use re-size for it.
Resize to 320% on vertical and horizontal, and do it AGAIN but use 200% for each. Making it life sized.
Make sure to use the magnifying glass to zoom away as far as you can, and strech the border of the paint, so the entire screen is white and not gray. Then Bring it back to cleanly fit around the supersized pic.
Attach each of the pages that print out in the right order (Easy to know how to do so), then cut so all your left is with the life sized rifle.
this will help although you'll have to get the measurements of halopedia.
oh and also all the weapons are as they apear in halo 1 so they may not be the same as any in halo2/3 needler pistol ma5b (ausalt rifle) shotgun sniper