The question seems to be; "can you bell/flair any case mouth whether it be rifle or handgun"? The answer is yes! The die required is the Lyman "M" die for rifle and handgun. Here's the one for 30 caliber rifles, they ARE
caliber specific. That means for one bullet diameter, like this one for 30 caliber.
http://www.midwayusa.com/viewProduct/?productNumber=129697
The M die has a two diameter expander plug that expands the main portion of the neck, then puts a bullet outside diameter straight section on the extreme front portion of the neck/mouth. This allows the bullet to be placed on the mouth, it will stay put while being seated. Some just leave the mouth expanded, shooting them as is. Others crimp slightly to remove the flaired section.
Another important point is the case can be sized with a FL or neck sizer with the expander left out of the die. This eliminates the need to lubricate the inside of the necks, and eliminates the drag that can pull necks out of line and lengthen the case. Some FL or neck sizers can be used without the expander ball but still deprime. Others use the expander button to hold the decapper pin. So you might have to decap in a separate step.
Here's a much better read on the "M" die than I can write, including pics of the "plug" showing the step;
http://www.lasc.us/Brennan_LymanMDies.htm
Lee also makes an universal belling die that simply puts a funnel shaped bell on any case.
http://www.midwayusa.com/viewProduct/default.aspx?productNumber=140461
Use of one of these dies is very important when loading cast bullets in rifle cases. All important to keep from shaving lead and lube from the sides of the boolit. Also if you're loading coated bullets like the Barnes or winchester coated, this will avoid damaging the coatings.