Isn't asking for a bottoming tap for a pipe thread indicative of a lack of knowledge of what a pipe thread is? The only pipe thread where this would be appropriate would be something like a British Parallel Pipe thread, but I don't think I'd want to use one with the types of pressures encountered in hydraulic steering applications.
If you cut the lead end of a pipe tap off, you will end up with a tap that only taps the largest dimension of a tapered thread. Doesn't sound like a good thing to me if you want it to withstand high pressures and not leak. Now, OTOH if you are trying to cobble a bulkhead type fitting, you might want a pipe tap with only the major diameter so the matig fitting can pass completely through whatever you tapped.
???
The part you are cutting off a NPT plug tap to make it a bottoming tap are the initial tapered cutting edges (IE removing the first 3-4 threads leaving a 1-2 thread chamfer) which assist in aligning and starting the tap into an untapped hole.
The "lack of knowledge" part comes when someone runs a NPT tap in far enough to produce parallel threads; most of us that have some experience chose to test the tapped threads with the fitting that is going in them at least for the first few holes tapped. Running a NPT tap in past the major diameter and producing parallel threads is going to be an issue whether it is a bottoming tap, a plug tap or a taper tap, the same goes for a NPT die set.
Using a NPT bottoming tap is a very common practice in blind holes where you need threads throughout the material but are unable to get a plug tap engaged far enough to provide a complete thread throughout.
Depending upon how clearance you have in the hole you are tapping you may need to take a few passes at trimming a NPT plug tap back enough to work as a bottoming tap but it easier to trim the tap twice than buy a new one when you trim too much the first time.
