Ideally you would want a prop shape that is optimal and designed for the application. In which the tip shape is important.
But for sport use (my example) we are looking to create a quick, easy speed prop from an existing piece. In some cases, this is done to best match the application and rpm requirements of the engine. The larger center hub of a larger prop is sometimes prefered. In which case, clipping an existing prop to reduce the load and allow the rpm to climb works fairly well.
The rounded tip shape is more a result of 'rounding over' or tapering the end of the blade due to the airfoil shape. Looks more like a P-40 wing tip.
As for the QM40 prop cutting.... I'm not sure there are any on-line tutorials or photos on this. Same as had been done for F-1 for years, just slightly smaller prop diameter. Darrol Cady's site has this info ....
http://www.darrolcady.com/Propellers...eller_faq.html
Basically for QM40 it involved starting with a Rev Up 400 serise or Zinger 9x7.5 pylon series prop as the master. First the pitch is checked on a gauge. (if the pitch on the blades was different, usually the hub had to be squared up a bit). It gets trimed it to 7.5" diameter. You then locate a point about 3/16" aft of the LE of the blade. Draw a line. Sand a flat from the blade TE to that line. (this thins the blade). Then it is a bit of finess rounding out the airfoil from that high point, and creating a properly radiused LE. They end up looking something like these shown here. In this case, note the tip shape. This one is typical for many that carve QM40 props. Some prefer rounded, others square. I rarely re-worked the back of the blade other than to correct the blade pitch. Some work carefully with gauges and micrometers to check the blade thickness and shape. In the past, we were looking for 0.100" to about 0.110" about mid blade (station 5 on a pitch gauge). The blade thickness tapers evenly from the hub to the tip, passing through that thickness and location. After final finishing and sanding, the blade ends up appx 7-3/8 diameter
Although these days the APC QM40 props have relieved many of us of endless work. Making 6 props, nearly identical, only 2 or 3 would be usable - the others didnt pull or turn up. Total crap shoot sometimes. For those good at this proceedure, they worked right or very close the first time. For me, I ended up re-working most props to thin them slightly or more commonly took another 1/16" or 1/8" off the diameter until the rpm was where it needed to be.
I was playing around basically making a bigger "QM" prop out of the 12" blade. It will take several iterations to get the blade thickness figured out just right.