I reload for .300 Win Mag, 338-06 AI, .270 Win and .45-70. (I load jacketed bullets, not cast.) I am intrigued by the possibility of improving case runout by removing the expander button from my sizing dies, and using Lyman's "M" expander die in a separate operation (after full-length sizing) to resize the inside of the case neck. Some have reported that they do this, in order to avoid having the expander button pull the case neck off center during the sizing operation. If any of you do this, could you tell me whether it has improved your accuracy? And have you measured runout before and after, to see whether it has actually helped?

I can't speak to case run out, as I don't measure it. I can tell you that not dragging the case over the expander certainly cuts down on case length change.

I hate trimming cases so much, this has become standard procedure for me.

I use the m-die all the time on new brass to get the "wrinkles" out. If you get the expander spindle adjusted into the center of your die you won't need to do this but if you feel so inclined it will work fine. There is a good shooter on another forum that uses a M die in his multistage press and swears he makes the best ammo around this way. It's probably the way the ammo manufacturers do things with factory ammo. You've probably notice that factory ammo is never chamfered. The only thing I can figure is they open the case mouth slightly (like the step on the m die), seat the bullet and then crimp it back shut.
I recently put together some ammo and left the slight "belling" ofthe case mouth there. Runnout was good and I figured the slight belling of the case mouth should help the case "center" better in a hunting rifle. They all chambered smoothly. It's fun if you can get your ammo to turn out real straight but I still believe that perfect runnout is overrated in a hunting rifle and the actual match of the "load" to the barrel harmonics make or break your accuracy--just my opinion and your mileage will vary!

Jimmy Mac and kraky: Thanks for your comments, guys.

I notice a lot of posts on these boards suggesting ways (some of which seem fairly complex and tricky) to get the expander button centered in the case neck during resizing, but very little about the simpler method of getting rid of the expander button altogether and using a Lyman M-die to size the inside of the neck in a separate operation.

(It seems to me that if the expander button is not centered, it is because the spindle that holds it is not centered in the die, or is not parallel to the axis of the die. Either way, I am not sure I see how you could succeed, physically, in centering it just by loosening the spindle and turning the spindle around its axis, and then tightening it down again. Maybe I am just not picturing it correctly, but it seems as though it could never be truly centered through that means.)

I experimented with my 7-08 dies. I believe I was neck sizing with a Redding die. Runout ran from .001" to as much as .007". After removing the expander ball and using the M-die runout went to .001". It didn't improve accuracy with the load I was using at that time but I have much better loads worked up now and would need to test with the new loads to tell.

I still do it regularly because the chamber is apparently on the small side on my 7-08 and using the expander ball stretches the case enough to make the bolt a little stiff to close. I shoot a lot of cast bullets in my other rifles so using the M-die is routine anyway.

If you try it make sure the case mouths are square. Also if you remove the expander ball you lose the primer punch. You can use an expander ball from a smaller caliber die set so it will still punch out the primer when you resize. I don't bother lubing the inside of the neck either when using the M-die.

Marc: Thanks; there are a lot of interesting facts in your post. One of the striking and unexpected facts is that you improved runout quite markedly by using that technique; but your accuracy did not show any corresponding improvement, with the load you were using at that time.

Bigbrass, that load had other things wrong with it. The rifle(Win Featherweight) was new at the time and very erratic. The reason I tried to reduce runout was because I was out of ideas. The rifle has settled down now. I am using a different overall length and I think the thing would shoot half inch groups if I could hold it consistent. It is a hard rifle to shoot off the bench. It is muzzle light and has a little skinny forend that likes to rock side to side.

I would have more faith in a retest now that I have a good combination. Before I tested it again I would need to come up with a better bench setup though.

I normally chuck up the expander ball in a lathe or even a drill press and remove about .003 or .004 from it, but not so much as to cause bullet seating problems...That solves a lot of problems and gives you a better purchase on the bullet, a simi tapered crimp so to speak...When used with big bore rifles in combination with a slightly compressed load it is as good as a crimp or works well with a very light crimp....