Alright, first a bit of the why and what this is. I hated the downward angle that the original stock of my vrbp-100 has. My best idea on how to fix this was of course with my new (less than a week at time of post) 3d printer. Since I am at least skilled in CAD and advanced measuring (you could roughly get where I got with a ruler) I was able to get at least good enough on the key dimensions on one interation of the base dimensions of the inside lip of the stock.
The process I use goes a little like this. Grab part, break part down to as many components you can, find key repeatable dimensions, use a common datum (begining point of a reference series of lines that makes sure you don't stack dimensions). The datum is absolutely important as said earlier you don't want to stack dimensions as thats how you stack errors. .010-.020 is about the range of accuracy you want depending on the part and if you have more than 4 or so features you can be off by a lot. If possibly use your calipers to scribe your measurements into the part you are measuring as this will help you reference features like bends or corners. If you can't "destroy" the part then its best to draw as you go and focus on the datum line first so you can get the X axis of your drawing. Using those datum points you will build the Y of the drawing until you have at least the outline points. This can get messy if your part isn't a perfectly straight piece, another way to help this is to trace the part onto paper, this can help you reference arcs and circles aswell by saving more datum points. You can basically average out the points until you have a relatively accurate translation of complicated arcs or geometry.
To split this up a bit, once you have all reference points entered and drawn out its time to connect all the dots. I recommend only snagging the key dimensions of the part first then using offsets to set your thickness of walls. You can generally use the first point in the datum to reference hole locations and such but you can use walls and such once you verify that your profile is correct through a test print and fit up. One weird thing about my part here is it has the 2d profile then it has a seperate 3d profile. I once again used the same datum and referenced common features and points to get the weird bend on the sides. I also used that drawing to make a reference body so I could use it to cut or merge that profile into other parts of the drawing. The original plan was to just make one giant holo spacer but I also had gripes with the buttpad as the first time I used the gun it straight up left a bruise, mag dumping a 9 round mag of really spicy slugs kind of sucked when it shouldn't have.
I'll wrap this up by saying a few of my favorite tools in cad. Revolve was used to actually correct the angle as you can use a flat face and it will form around a reference point with no diviantion in side walls. Merge is also another fantastic tool that lets you take a straight 3d model and impart a profile into it with a reference drawing. The one other thing that saved me time and heartache was the move function as I had to cut and move pieces a few times during the final revision.

Quick note, I used a pair of calipers for every dimension and finished the part with a pocket knife and small file, I miss having separate support materials but hey the printer costs less than a canister of material for the industrial printer I had access to in a previous job.

Thanks for the support here, I look forward to sharing a much more time intensive project or two for the summer rust. This really was just a lets see if I can fix something real quick. In total I probably spent 2 hours on the drawing, I had a failed print out of 4 between the test profile, v1, and v2 prints. Either way good luck and hope some of this helps!

Winter Rust 2024: VRBP-100 Inline stock print and a few tips for translating geometry into CAD from a physical part.