260 Brass from 308 - My First Go

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It wasn't hard to find threads on the subject of forming 260 brass from 308. It seems the most common method is to FL resize to 7-08 and then again to 260 making sure the inside of the neck is properly lubed in addition to the rest of the case. Some people neck turn, some don't. I wanted to establish whether or not I would need to neck turn and here are the results of my 2 step resizing process. Before resizing, I trimmed the brass to 2.011"

I measured the length, neck outside diameter, inside diameter and wall thickness each step of the way and this is what I got:

.308 Win Brass
Length - 2.011"
Neck Outside Diameter - 0.332"
Neck Inside Diameter - 0.308"
Wall Thickness @ Neck - 0.014"

FL Resized to 7mm-08
Length - 2.018"
Neck Outside Diameter - 0.309"
Neck Inside Diameter - 0.382"
Wall Thickness @ Neck - 0.014" (unchanged)

FL Resized to 260 Rem
Length - 2.024"
Neck Outside Diameter - 0.289"
Neck Inside Diameter - 0.262"
Wall Thickness @ Neck - 0.014" (unchanged)

...then I seated a .264 bullet and the neck outside diameter grew to 0.291"

Is this consistent with what you guys have found? Here's a photo with the new 260 on the left and the 308 on the right. You can see the old shoulder on the 260. Should I neck turn it? If so, should I neck turn before or after resizing? I don't have the rifle yet so I don't know if/how they'll chamber just yet. I was expecting the neck walls to get thicker but they didn't. That brass had to go somewhere so it either went up or down, or both. The cases are 0.013" longer which solves half of that question.

260rem.jpg


It's my first go at forming cases from other cases so I appreciate any input you fellas have. :D
 
Is the barrel a custom? If so, what is the chamber neck diameter? If not a custom, then I would wait until you get the gun and fire some factory loads or factory 260 brass, and measure the neck OD. If your resized 308 brass is 0.002" less than the fired brass I would not neck turn. Did you start with good brass like Lapua?
 
I'm not 100% sure, (I formed mine from Lapua .243) but I think you should be turning the necks down. I turned and reamed mine out after fire forming the .243 brass, because a small ridge forms from the shoulder becoming neck.
I would ask the same question as Ron, are you starting with quality brass like Lapua? If you are just using cheaper brass, why not just buy the correct .260 brass?
 
Ron AKA said:
Is the barrel a custom? If so, what is the chamber neck diameter?
Click to expand...

It will be a Shilen. I think it's best to fit my brass to the chamber, not the other way around. Prudent?

Ron AKA said:
Did you start with good brass like Lapua?
Click to expand...

Winchester :D I have a bunch lying around here and had no trouble finding dies. Made for a good first try because if I messed it up it wouldn't cost me any sleep. I have not found any 260 brass as of yet. If anyone knows where I can find some, I'll be happy for your help! EDIT: Found some 260 brass this morning.
 
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Opening a .243 case will likely result in a dreaded donut (inside ridge) in the neck, which many ream out. Sizing down won't.
 
Don't turn anything until they are once fired. That "bubble" at the bottom of the neck will iron out into shoulder material once it is fired.

I turned my .308 brass prior to necking it down.

I sized mine in one step 308 - 260 in a FL RCBS 260 die then fireformed using CoW and pistol powder to iron out most of the shoulder before going to full house loads.
 
Cream of wheat. Do NOT use a filler and a bullet.
I prefer to simply load the rounds, and shoot them, rather than fireforming with a filler. They shoot just fine, and this avoids an extra step.
 
Pistol Powder in bottom of case.

CoW to fill the case to the bottom of the neck.

Small ball of paper towel/toilet paper to keep the CoW from falling out. Some use crisco/lard but the paper is less messy I think.

If you separate a sheet of 2 layer TP and tear into 4 or 5 even pieces this is usually sufficient to make a ball large enough to friction fit in the .260 neck. Just be sure to tuck any loose ends into the case neck.
 
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