I have a Remington 700 SPS Stainless in .270 WSM. The cartridge neck portion of the chamber of this rifle measures 0.3162 in. Factory loaded .270 WSM rounds from Remington measure 0.3095 in. at the neck. This yields a clearance between the cartridge neck and the chamber of 0.0067 in. While this rifle will be used strictly for hunting, I will be reloading for it and am interested in both accuracy and maximizing case life. If I neck turn .270 WSM virgin brass to improve accuracy, it will result in even more neck clearance. Is this amount of clearance detrimental to case life? I am thinking of resizing .325 WSM brass to .270 WSM to achieve thicker necks, then neck turn them slightly for concentricity. If I do this, what clearance should I aim for to achieve reliable feeding thru this hunting rifle? Could I run the .325 WSM brass directly through a .270 WSM full length sizing die or is an intermediate operation (say, thru a .300 WSM full length die) advisable to improve yield? Thank you.

Welcome to the world of SAAMI chamber dimensions !!!

The neck clearance will not effect case life, but in theory it is not good for accuracy, since it does not help position the bullet concentric with the axis of the barrel. That's why benchrest shooters have custom chambers that require turning necks for a perfect fit with minimal clearance.

For a hunting rifle, about 0.002" neck clearance seems desirable to me.

I doubt if you will see a huge difference in accuracy with fitted necks, but if you try it, let us know how it turns out.

You'll need about .002" of clearance between loaded neck diameter and chamber inside neck diamter for safe bullet release. You'll need more than that in a hunting rifle - maybe .003-.004" - to deal with inadverse conditions such as dirty or wet ammo.

A neck clearance of about .006" is not uncommon for a factory rifle, and is one of the reasons it probably does not pay to turn necks for chambers like this. Tolerances are just too sloppy to really reap the benefits. But, the idea of necking other cases down to achieve a thicker neck and then turn is one used with other cartridges as well.

Is it worth it?? That will depend on you. I would personally try regular .270 WSM cases first, and see what I could get out of that brass by ensuring minimal runout, play with seating depth and powder charges for the best accuracy. Actually, the biggest effect will probably come from finding the right bullet - I would start with a Nosler AccuBond and a Barnes TSX, both in 130 grs.

Good luck.
- mike

Oh yes neck clearance does effect case life and here's how it works. If you have alot of clearance, like in your case, and you use a reloading die that sizes the neck down excessively, the the expander ball sizes it back out to the proper inside diameter.....you end up with a lot of brass working..which hardens the brass and the end results are neck splits...unless you anneal them again. This is the reason for Redding (and other brands) neck bushing type sizing dies. That's so you can choose a diameter that will resize your necks without over sizing them.

Joe

I don`t think 0.006" is too much on a hunting rifle. 0.003" may be prefered but as noted by another poster the tighter your chamber the more keeping it clean and case wall variation will have an effect on bullet release. Turning case necks in a chamber of this size will mean more working of the brass as you now have to squeeze a thinner -smaller OD- neck down farther to have the same tension on your bullets. You may or may not be OK with the die you now have but, then again you might have to get a new die or use a smaller "Button" if you use that type now to get acceptable grip on the bullet. This will increase the work hardening of the necks and reduce case life. A new lot of brass or different manufactures case also might be thicker or thinner then what you now have. A change in cases may reduce your clearance to 0.004/5" or increase it a thousanth or so.