Leaving a little bell to "scrape" the chamber walls is fine, as long as it chambers well, and also isn't a hunting round. It also depends on how your bullet fits the case neck. If it slips in easily, then this slight flare might not be an option as the bullet wont necessarily stay where you seat it without a slight amount of friction.

I think neck tension is real important and best way to set it is with bushing neck sizing dies. I size to about .oo2 smaller than bullet diameter. Not a lot of squeeze but enough to hold the bullet secure not work the brass excessively and most important not deform the bullet. 

Other advantage is you can use one die and size several similar cartridges by changing bushings. 25 Kraig 30/40 32/40 38/55 all with the same die. Bushings from CH4D are 12.95, cheap enough to play with how much to size the brass. .oo2 is a good starting point may not be the best for all. Way the bullet feels seating and pulling out is a good indicator. Loose slipping is not a good idea, too tight deforming not good either. 

I have a lee "factory crimp" collet sizer for 30/30. Ok to turn out some jacketed hunting rounds.  Not my go to solution for accuracy work. 

Boats.

You got me rolling on 38/55s. I have been shooting the same CPA 38/55 since 1993. Good results in local matches guys often ask me how I load mine.

Problem is 38/55 varies a lot depending on several things. Origional guns most often .380 bore. Italian reproductions too. American small shop reproductions mostly have .375 bore , barrel blanks intended for the common 375 modern cartridges . Dies vary too. I think Lees 38/55 dies are actually .375 Winchester dies stamped 38/55 Others intended for .380 bore guns.

Only way I know to get it "right" is mike a fired case from your gun so you know what you are working with. With O/D of a fired case, case wall thickness, and bullet size you can calculate how much you want to squeeze down the neck when re-sizing. 

This assuming the bullet size is right for the bore .

My .375 barrel shoots best with a .377 cast bullet. Case necks are sized to give .375 inside = .002 bullet pull.  To get the outside right for .375 inside I have to know wall thickness, from memory my Winchester cases are .011 double it and add .375,  I need to size the outside to .397. 

Your outfit may need different. Use my dims for method,not actual.

Make sense ?

Boats

You can decide if this is relevant to your question and application or not...

The old Speer manuals #8 (page 330), and #9 (page 344), contain a short note about the results of a test conducted in the Speer Ballisitc Labaratory regarding the application of differing amounts of crimp.
Their test used the 38 Special case, loaded with 5.0 grains of Unique, and a 158 grain lead bullet.
The results were:
Quote: