I am a new user/customer so there is little doubt that some of my issues would be resolved with patience and practice...thanks for the opportunity to ask questions in this way. I did not see any other posts addressing this issue…
The bullet is to be pure lead or 2% tin alloy for low velocity (700 - 950 fps) use in an air rifle. Since air rifles do not use cartridges there is no need for a crimping groove. The caliber might be.308 or .338 and about 100 - 150 grains if .308 or 175 – 200 grains if .338.
Since bore friction, swaging the bands into the rifling and obturation are the major impediments to getting the bullet down the barrel and up to speed, I have reasoned that a bullet with minimal bore contact area might be a good idea for the low energy game I want to play.
A bullet with the shape of a sewing thread spool came to mind, a long body/groove separating narrow bands far forward and back, perhaps with a short wadcutter nose or a tangential ogive. It looks like your software demands a minimum meplat diameter.
Now my question is this: when I vary the bullet weight, nose shape or band, groove and bullet length dimensions I get aberrant lines on the display. Sometimes the ogive comes to a point with an inverted triangle sitting atop it.
How do I know when I have arrived at a tenable design, something you can actually make?
Another way of asking the question is "how do I know when I have asked the CAD function to draw something that is physically impossible?"