Neck question

[Dan B]

I am looking for some insight on case necks and neck sizing;
Specifically I am reloading for a .243 using Winchester brass (I have tried a couple different case lots), the necks on loaded rounds measure .270" (.0135" neck wall thickness) , necks on fired cases measure .275".
Would a die that sizes to .269" work?

Reloading for this in the past I would back off the FL resizing die, the cases would chamber easily and accuracy is fair (3.0" at 200 yards), however I am getting neck splits after 2 to 3 reloads, after firing the necks are sooted to the top of the shoulder.
Could the chamber neck dimension be too large and the brass being overworked by necking down .006" each time - should I be looking for brass with thicker necks? would annealing be an answer?

The rifle is a Remington 700 used for deer hunting (90 gr bullets) and some varmint hunting (70 grain bullets), I am trying to get a little more accuracy and better case life.

Thanks,
Dan

 

[Ganderite]

Typical factory chamber dimensions. Case is not being over-sized. Nothing you can do about it.

Soot on neck suggests case is under-loaded.

 

[paperslayer]

5 thou clearance is at the top end of SAAMI spec for chamber clearance but that has nothing to do with neck tension... Unless you use a bigger or smaller diameter bullet, the cases will always come up to 270 with a bullet stuck in the neck If the rounds are measuring .270 loaded with your bullets, I would go .268 if single shot feeding and .267 if mag feeding. In some cases, such as the 6BR, I ise a 6mm expander mandrel after re-sizing to bring the neck tension down even more, but that is not something I would recommend for what you are doing.

Split necks are the result of having to work the brass so much with such a loose chember in the gun (Each re-size and firing expands/resizes 5 thou) Sooting is an obturation problem and that means you are likely not loading stout enough, or with the right powder to bring the pressure to where it needs to be. The cases will simply crap out unless you get into annealing. I might suggest using some Lapua brass. It is pretty tough stuff, but all brass becomes hard and split-prone with lots of re-sizing (without annealing)

.268 or .267 will do the trick. for a bushing.

 

[Dan B]

Thanks for your help,

The loads I am using should be near max by my chronograph and manufactures data:
22" bbl .243
70 grain NBT over 47.0 grains of H414 3420 fps
85 grain NPT over 44.0 grains of IMR 4831 3075 fps
much higher and I get pressure signs, are there other causes of sooting?

It sounds like I should not worry about a neck die if my current die is sizing in the .267 range and maybe spend the money on Lapua brass.

Dan