The .31-06 Lee collet auto-flare

[Spindrift]

Like probably many of you, I like and use the Lee collet die for neck- sizing my rifle brass. It is an affordable, effective tool that creates good cartridges. After sizing the necks, I expand and flare the necks using the appropriate expander plug.

Lee offer many spare die- parts, and sometimes these can be combined to change the functionality of the tool. I wanted to modify a 30-06 LCD, so it set neck tension to 0,0015in with .310 bullets, and left the case mouth unsized/flared.

Regarding neck tension, you can adjust this by the position of the die. But this would not be a «set and forget» adjustment, as another brand of brass would be different. Better then, to have a mandrel of the appropriate size. Lee offer a mandrel for the .303 Brit, which is the same length as the .30-06 (or .308) mandrel. The original .30-06 mandrel was .3057, the .303 Brit was (forgot to write it down!) about .3075.

I did some measuring and calculations, and found out my die with the original mandrel gave an internal diameter exactly 0,002in larger than the mandrel. Since I wanted an internal diameter of .3085 after sizing, I honed the .303 Brit- mandrel to .3065. Easily done, by chucking the mandrel in a cordless drill.
The hole in the sleeve also needed to be enlarged a little, easily achieved with a drill, brass brush with some steel wool and grinding compound. There should be some play between mandrel and sleeve, to allow for dynamic alignment.

In order to get the auto- flare function, some material must be removed from the collet fingers, so the case mouth remains untouched. I used a conical grinding tool designed for Dremel- type grinders. With a little tape on the shaft, it was a snug and centered fit in the trim-guide hole of a case trimmer. I used a fird, unsized, decapped sacrificial 30-06 case for «collet holder», to keep the collet reasonably centered and level.




Grinding this by hand was time- consuming, but very controlled. And the result seems to be quite good. And in the long run, this should save me quite a few pulls of the handle, as I shoot a lot of 30-06 cast bullet loads.


Edit:
PS the "auto- flare" function is not my idea! I learnt it from Ian!

 

[Ian]

I think some guys on the CBA forum modify the fingers in similar fashion to what you did, though they probably have lathes instead of the ingenious non-lathe solution you came up with.

Good to know about the .303 mandrel, I've used the x39 EZ-Expander spud for my .30-30 Lee full length sizing die for many years after enlarging the neck slightly, works great for fat cast bullets in the Marlins. If I'd known the mandrel sizes I wouldn't have made one from scratch like I did for my '06, it's a pain to do although having the rebated portion reduces drag.

 

[Maven]

I was fortunate since my '06 Lee Collet Die came from the factory with enough taper, if that's the right description, to allow CB's to be seated without flaring or using my Lyman M-die. Quite a timesaver! Alas, my .243Win. collet die set didn't allow this, even after modification. It's no longer an issue as I sold my Ruger #1 in that caliber last spring.

 

[Spindrift]

My .222 rem collet die is also like that, it leaves a flare on the neck.

Ian, you made a beautiful mandrel! I see your point with the rebated section, my mandrel works OK but there is a hint of drag that is slightly annoying. Might have to do something about that.

 

[Bret4207]

Cool! Nice to see some clever adaptations for better results!

 

[Matt]

You can achieve the as fired neck flare with the Lee collet die by shortening the collet by the amount of case mouth you want left unsized. It’s a five minute job with a fine cut file. I deburr the inside of the collet with a twist of a case deburring tool.

By adjusting your die you can set the inside diameter of the case neck. Using my .308 collet die as an example I can achieve an inside neck diameter from .305 to the as fired diameter of the case. You need a set of gauge pins to adjust the die properly. If your case neck wall thickness is uniform I’ve found that the necks are straight as are the loaded rounds and results are very consistent. Running a brush in the neck to clean before sizing helps too.
I adjust my modified collet dies for an inside diameter .001 “ smaller that the diameter of the cast bullet. This makes it easy to fit the necks to various bullet diameters as you search for the best accuracy.

I can’t say that this method is more accurate that using an M type die to set inside neck diameter and flaring, but it is much quicker and a lot easier on the brass.

The Lee collet dies are a very versatile tool.

 

[Maven]

Another solution to the problem that I just remembered is to size a case and then ream the inside of the neck to the depth of a gas check. You need to do this only once, and it works.