Aliens M41A Pulse Rifle - Measuring the Thompson.

Before proceeding with the rest of the pulse Rifle, I'll need to spend time looking closely at the Airsoft Tommy gun I'm using as the base. 

To start I'll need to remove the Thompson's stock, foregrip and rear sight.

The Stock and Foregrip are each held on by 2 screws.  Unscrew them and the parts pull right off. The gun's battery is normally housed in the stock, so i'll have to reroute those wires and create a new battery holder somewhere in the rifle.

Removing the rear sight was a bit more tricky, involving removing the upper receiver and unscrewing four small interior screws. With the grenade launcher and the reference model, we can start to see the basic shape of the pulse rifle.

I need an accurate digital representation of the Thompson to work around as I model the body of the pulse rifle. With calipers and a bit of patience, I reconstructed the Tommy Gun inside sketchup.

I didn't bother measuring and modeling the pistol grip, because there is no part of the Pulse Rifle body that touches that area. No need to waste time accurately creating something I won't need. 

The most important parts of my digital reconstruction are the places where the Pulse Rifle body will touch the Thompson. To confirm the accuracy of those areas, I created test geometries to 3D print and fit onto my real world Thompson. If the parts fit, my measurements are accurate, and I can get started on the hard part.