Resizing .308 to 260 Ackley

[codyadams]

So my Krieger barrel is shipping Monday, going to replace my factory Remington .308 barrel. I also have 100 rounds of once fired lapua .308 brass, and since I was planning on neck turning for accuracy anyway, and 308 is much cheaper to buy and I have to fire form anyway, I want to use 308 brass in this gun.

So my questions....

Can I just run my 308 brass through my 260 AI die to resize, then trim/chamfer, neck turn and be ready to load and fire form?

Also, how much clearance do I want between my loaded round neck diameter and my chamber neck diameter?

I plan on getting an RCBS hand held neck turning tool, but was also looking at the Hornady. I have not neck turned before, but I know I will have to if I'm using 308 brass sized to 260, and I want the most accuracy I can get out of this rifle.

Thanks for any suggestions

 

[RT2506]

When necking down 308 Win to standard 260 Rem your necks will be quite a bit short. I don't know if they will be shorter AI-ing them. 243 Win cases make perfect 260s.

 

[MudRunner2005]

When necking down 308 Win to standard 260 Rem your necks will be quite a bit short. I don't know if they will be shorter AI-ing them. 243 Win cases make perfect 260s.

From my experience, necking-down brass the necks get longer, because the brass is getting compressed, and the excess has to go somewhere.

When I neck from .270 Win to .25-06 for forming into .25-06 AI, I neck them down to .25 cal, then trim them .020" too long, so when they are fire-formed, they're the perfect SAAMI length.

 

[codyadams]

When you neck 243 up to 260 and fire form it in a 260AI chamber do you get donuts? Is there anyone here that can speak from experience on this matter?

 

[RT2506]

The reason that the necks turn up average 10 thousands too short when going from 308 to 260 is the 308 starts out shorter than what is needed. We never got donuts when necking 243s up to 260. My hunting buddy got one of the first Rem 700s in 260 Rem to ever come out. It was before he could even find any ammo. There was not even any published load data out yet. We tried different cases, 308 and then 243s. We just ran Remington 243s in a FL RCBS 260 Rem die and they worked great. We did some extrapolation of 6.5x55 load data and chose H4350 and started doing a slow work up. We were using 120 and 140 gr Sierra bullets. We ended up with a little more charge than is recommended in the data these days but from the case measurements and how long they lasted we were not too hot for this rifle. That thing was accurate and we were doing crop damage control back then and that year between us we killed 52 deer with that rifle from on top of us out to around 600 yards. One shot each and only one moved out of it's tracks and it made three jumps and pilled up because from what we decided was because the bullet hit a cotton stalk and deflected it slightly and it just caught the back of one lung and the liver. We used both 120 and 140 gr Sierra SP bullets and they were both very accurate and was not much difference in POI until you got past around 350 yards and then the 140 started to shine.