What is the process of changing .308 to .260rem?

Run a well lubed case into a .260 die. If it crushes the case then run them through a 7-08 die and then the .260 die.

Unless I had a free supply of .308 cases I'd just get some of the great Lapua .260 cases and call it good for a lifetime.

I've been loading and shooting the 260 since it arrived in Remington's model 7.

I have NEVER loaded a 260 case. All my 260 cases are reformed 243win cases. Just lube them up, run them into the die, load them as normal, and shoot them.

Using 308 cases will require turning the case necks and other tedious work. Stick to 243 cases.

708 cases will work also

Having made LOTS of 708 and 260 Rem cases out of Federal Gold Medal 308 I can tell you my experience. Typically, I make a neck turn pass on the 308. I then lube it with STP oil treatment and run it through a 708 die and then through a 260 die. I then make a final neck pass to final dimension. IF you only make your neck turn once it is already necked down, it will create a substantial 'donut' at the neck/shoulder junction.

I was really glad when Lapua made the 260 brass as the R-P brass was pretty crappy in my experience.

I've necked down a lot of 308 range brass to 260 Rem, in Rem, Win and Federal brass. Even tho I got the donut on the neck when done the first time when going from straight 308 to 260, it has always chambered with no problems in my Rugers, My Rem VLS and a few aftermarket barrels on Model 70s....

I tend to run a lot of Win 7/08 brass for my 260 needs tho...

never had to do any neck reaming...

Chambering is NOT the problem, the donut will mess up your bullet seating if you use bullets heavier than 100 grains.

Ya wanna expand on that Dennis? Because if there is a problem, my rifles sure haven't shown it....but they are also not tight chambered...I've had them throated out to accept bullets at magazine length...

When you size 308 brass down to 260, part of what used to be 308 neck is now 260 SHOULDER and is thicker. Where this junction is there forms a shoulder of thicker material. When you seat a bullet it hits this shoulder of the bullet is long enough to protrude into the shoulder area. If you have a tight enough neck you can take a fired case and drop a bullet back in it which will bottom out at the shoulder. If it is too loose and slides through, you can take a bushing and size it down enough that the bullet can go in snugly with finger pressure but still sits on the donut.

What I do is chuck the K&M shell holder in the 3-jaw and spin the case. I then go in with a chucking reamer and shave that donut off. You can also buy a carbide mandrel for about $40 from K&M that will cut the donut away when you feed it in during the neck turning process.

By shaving most of the excess neck away BEFORE you neck it down you mitigate this donut problem. The donut is one of the reasons when radically case forming you have to inside neck REAM.

I have literally made thousands of 708 and 260 cases from once fired 308 Gold Medal Match cases.

And at the moment are likely easier to find. .243 brass is also more likely to be available, and the 0.5mm either way is pretty effortless.

Thanks Dennis for the explanation..

Thanks to everyone for their comments. Since I don't turn brass I need to forget the 308 brass and get some 243 or 708.

I have used 7/08 necked down when I couldn't find .260 brass. No 'problem' noted with the donut issue in my Ruger hunting rifle-deer and coyotes have never noticed! There is probably a bit of one there but it isn't an issue in my situation.

In my more inoccent days I used to neck down .308 brass to .243 for use in my Sako AII, with zero thought given to the necks, and zero problems.