Possible
Maybe beside the point, but what do you mean by "fit easily into the case mouth"? If just starting into the case mouth, OK. If any further than 1 mm or so, I would worry about tension.
Yeah, if there is a slight (narrowing) taper to the bullet, you may indeed not have to bell the case mouth or even expand the case neck in order to seat a bullet. You would probably find better stability in your rounds during handling and consistency in velocity and accuracy.
Drawback is that if the case neck is insufficiently belled or expanded, you may crush or wrinkle a few cases (due to tilted bullet placement or just the greater neck tension causing the case walls to collapse). Small price to pay for being able to safely skip a step and get more consistent ammo to boot. Just be sure to measure and fit your finished product (also known as Quality Control "QC" or Quality Assurance "QA").
Test your finished ammo (every round at first) to ensure they will chamber (at first in just the chamber of your disassembled gun) and that you don't get cycling problems through your magazines and action of a small quantity run and lastly, that the ammo produces the cycling, pressure and velocity you expect.
After that, statistical sampling of size and cycling that all reloaders do.
You are using the scientific method to operate in your private ballistics lab and your personal ammunition factory. You are on your own, so be safe, always, all ways.
You are doing well to think about the issues, design a methodology, check with other loaders, and then proceed with caution. Scientists do this all the time. They formulate a theory, check the literature to see if someone else has previously worked on the same or similar theory, design an experiment to test the theory and evaluate results.
Go forth and prosper.
Lost Sheep
By the way, if those bulets are smaller at the base than the diameter throughout most of the bullet's length (before the ogive), I would call those bullets tapered. But I am sometimes generous with terminology.
