308 cal case 311 boolits .. why not use a 310 expander Ball is a RCBS die

[Smoke4320]

so just wondering : on a 308 cal case with 311 boolits .. why not use a 310 expander Ball in a RCBS resizing die.. and a lee universal expander (to bell the mouth). Why do most here recommend a lyman M die. does the M die resize the inside and bell the mouth ?
edgemacate me :)

[ku4hx]

My "M" dies are 30 years old, and they all inside size the neck and flare the mouth. Try the .310 expander ball and see how well it works. It might do exactly what you want it to do ... it might not. If it doesn't, you can always start over with a full length sizing operation.

[Larry Gibson]

If the .310 expander expands the inside neck diameter to .308 - .309 then that should work fine as far as seating the cast bullet goes. Problem is that dragging an expander ball that much larger through a neck sized down for a .308 bullets can cause uneven expansion of the case neck resulting in some pretty crooked necks depending on the elasicity of the case necks in question. Crooked neck = non-concentric bullet seating = not the best accuracy.

Larry Gibson

[runfiverun]

I don't pull the bigger ball through I push it in.
with 310 boolits I use a 310 ball I polished down to 3095.
I let the neck spring back from that.

[462]

The M-die does it all in one operation, rather than two. Also, the M-die makes a parallel opening, instead of a flare, allowing the boolit to sit square in the mouth and not wobble about.

[runfiverun]

which would be awesome if the chamber wasn't tapered.

[leadman]

The "shelf" that the Lyman M die creates in the neck allows the boolit to sit inside the neck so it is started straight, something that the Lee Universal flare die does not do. The M die also expands the entire neck so the boolit is not swaged down when seated in the case. Most die sets size the neck for jacketed bullets which is usually too small for cast. So even if you use a .310" expander ball when sizing the neck is first sized down to as small as .305", then opened back up to .310" when the expander ball is pulled up thru the neck. Size your case with no expander ball and measure the inside of the neck.
I set my seater die to just take this expanded part of the case neck back down to just touching the boolit on most of my cartridges. If the chamber in the neck area is excessively large like most old mil-surp guns I either leave the expanded neck alone if it chambers freely or take just enough expansion out of the neck so it does chamber freely. I think this helps center the neck in the chamber. For a lever gun you would want to crimp the neck.

[Shiloh]

I have a decapper/mandrel from a .303 British die in my .30-06 neck die. I use an M dia as well.

Shiloh