260 remington brass from 308 or 243...which is preferred?

[Jasper243]

I have been unable to find 260 remington brass locally, so I am waiting on an order from Midway.  To get by this weekend, I was hoping to form some from either 308 or 243...Is there a  preference to necking up or down?  The first couple 308's that went down left the base of the neck looking a little funny, and the bolt is tight to close.  The 243 necked up looks much better, but is still a little tight on closing the bolt.  Will the bolt always be a little tight until brass is fireformed and resized again?  I appreciate your input on proper sizing/fireforming of 260 cases.

Jasper243

[beemanbeme]

Assuming that you do not own a .243, I've had good luck going from .243 to 7-08 and less good luck going from 308 to 7-08.  By going up, you avoid the possible need to have to neck turn.   
The down size of going up iis, if you own a .243 there is a chance you could grab the wrong ammo and have it fit.  I seriously doubt, considering how little difference there is between a .243 and a .260, that you  would end up with smoking shards of steel in your hands (and perhaps head) but it might be embarrassing.
Often resized brass is a tight until fire formed.  Make sure the length of the case is within specs.

[wncchester]

I don't make 260 at all but I have long made 308, 270, 30-06, 243, 22-250 and 6mm International from Remington .35 Whelen brass.  I prefer to neck any case down rather than up because necking up produces thinner necks and most brass is already too thin.  Of course I do have to turn the necks (and anneal them) when going to the extremes but that lets me configure the finished necks to better match my chambers.  Therefore, I suggest you start with .308 cases, doubting you will need to turn necks from such a slight reduction but measure the finished rounds before shooting just to be sure. 

If you are already having trouble chambering your formed cases, examine the shell holde-to-die fit WITH A CASE FULLY INSERTED IN THE FL DIE!   If there is a gap, reset the die to eliminate it.  Just setting dies to "make contact" withiout the pressure of FL sizing almost always results in a bit of "slop" between them.  That means your cases will be slightly long when sized, base to shoulder, due to the bit of normal spring in the ram/lever linkages. 

It is also possible that you have a maximum headspace die and a minimum headspace chamber.  If that is so, it is essential to adjust the FL die under pressure for propely fitted ammo.