I ordered two types of helmets and a rifle from Shapeways.
I ordered an 1:22.5 (the closest scale to mine that was available) M-1 Springfield rifle for my sentries from Shapeways but there was a production problem, so I was given a refund. One fifle is quite pricey when ordered in the finest finish - just a warning to others. What to do? I found a drawing of one on the internet and learned the prototype was 43.6 inches in length. Doing some simple math with my scale of 1:20.3 I calculated that my model should be 2.15 inches long. With trial and error, I used a program in my computer to reduce the drawing I saved to my computer by 25%. Voile. I got a drawing that was a tad over 2" long. I printed it out and was about to glue it to some thin scrap styrene I had on hand. Then I realized I could take a slightly expensive detour and print it on Avery 5165 8 1/2 x 11" Shipping Labels. They are a buck a piece so they are not to be trifled with. I then trimmed the art and peeled off the label backing and affixed it to styrene.
Warning, when I flexed the styrene to snap off excess styrene, white stress marks appears throughout the paper. That can be touched up with a brown fine tip marker I have at my workbench. I will also touch up the white edges of the rifle. Right now, I will use this to cut and adjust the positions of the sentries arms so he can hold the rifle. Will I ever purchase an expensive 3D printed rifle? perhaps not; I probably will be satisfied with how this mockup appears from a distance.