260 Rem, Lapua Brass, neck up or down?

[JRinCo]

Using an intermediate step is not necessary or desirable. Your brass will turn out far more concentric not to mention straighter if you size down using a full length sizing die.

And also necking up .243 brass, is as good or better than necked down brass. And whichever way that you go, neck wall thickness will still be between .014 to .015 regardless.

I’ve gone through a bunch of .260 barrels and I’ve always used a .290 neck chamber. You neck turn the brass to a finished, loaded .288 dimension (which is just enough to clean up the neck). As long as the brass has been turned and resized correctly, every round chambers flawlessly. Using .294 chamber you necks will wear out quicker and you will be sacrificing accuracy with that much clearance.

 

[AKDaddy]

I went with a .294 neck since there's a good chance I might hunt with this rifle some too. For that reason I wanted to be able to go with a "no-turn" neck diameter in case I need to shoot factory ammo, or someone else's, which is unlikely but possible. It also allows for a bit more clearance for grit with my own (cleaned up neck) handloads. I was hoping to end up with brass that cleaned up close to about .290 loaded diameter, which I think shouldn't cost me too much accuracy or necks that wear out too quickly.

I'm building this rifle as a tactical/hunting rifle, not purely for accuracy, although I'd like to squeeze what I can out of it. That means some sacrifices at both ends, meaning a rifle that's a little heavy for hunting and not built as tight as a bench-rest gun.

Just for reference, another forum member provided me with a little data: a Berger 140VLD seated into necked up lapua .243 brass has a loaded neck diameter of .2925. Necking down from .308 might bring that to .293 or .2935. I'm hoping that will leave me enough extra thickness to neck-turn down to .290-.291 and end up with perfect necks.

 

[30378]

Neck the 308s down and turn to the liking of your rifle.

 

[AKDaddy]

I did a little more experimentation this weekend.

I necked five Win 7-08 cases down in one step using an RCBS FL die with the expander button removed, then expanded with a Sinclair expander mandrel.

Then I necked five more 7-08 cases from the same bag down in 3 steps: full diameter (.311) to .305, .305 to .299, then .299 to .290. using my Redding FL bushing die and just changing out bushings.

The cases necked down in one step with the FL non-bushing die definitely showed more warpage (in particular belling at the case mouth) than those necked down in three steps.

I also got my tubing micrometer in the mail. The cases I necked down and neck turned earlier ended up with a wall thickness of .013 after neck turning until there were no more high/low spots (ie the entire neck was turned). Loaded round neck diameter with these cases ended up (predictably, after adding a .264 bullet) to be right at .290. I'm going to turn the necks on the brass I did in three steps some time this week and see if they show less variation in brass thickness. They already seem to show a lot less uneven stretching at the case mouth. My hope is to be able to make cases that leave me with .291-.292 loaded round diameter (ie require a little less cleaning up) and trim square without losing much neck length. I was looking forward to testing my new K&M neck turner, but unfortunately ABF shipped it without the case holder! Dang!