260 Brass neck thickness question

[bdcook]

I know the subject of forming 260 from 308 brass has been covered alot on multiple forums and sites but I guess I am unclear on something.

I went out and bought a bag of new Winchester brand 308 brass. I ran 5 cases through my 260 dies and then loaded 5 dummy rounds with 123gr A-Max bullets. I measured the outside diameter of the necks and the top and bottom of the neck.

Top of the neck measured .292-.293
Bottom measured about the same .292-293

From everything I have found this is .004 to .005 thousandths under the sammi spec.

I tested a couple with a paint marker on the neck and got no major rubbing of the paint.

I did form a piece of 243 brass and it chambered very easy. the 308 brass chambers with slightly more drag on the bolt handle.

I assume that this means this brass should be good to go. I know this is not directly measuring the thickness of the neck brass so this is why I wanted to ask. Also this is not a competitive gun. I am just shooting around the farm and friendly competition with a few friends that shoot together.

Any help would be appreciated.
Thanks

 

[thatguyshm]

According to SAAMI, you are close but not over .2970. Granted, chambers are different. If you can neck turn, try taking a tiny bit off. What is the neck thickness, straight up and down when you size down? As in, stick your caliper tip in neck of the case and measure just wall thickness, not neck thickness after you have sized down. I size up to 338 federal often, but I don't have anything I size down for yet. I turn my .223 down to around .0135" or so. Give or take. Food for thought, wish I could help more.

SHM

I know the subject of forming 260 from 308 brass has been covered alot on multiple forums and sites but I guess I am unclear on something.

I went out and bought a bag of new Winchester brand 308 brass. I ran 5 cases through my 260 dies and then loaded 5 dummy rounds with 123gr A-Max bullets. I measured the outside diameter of the necks and the top and bottom of the neck.

Top of the neck measured .292-.293
Bottom measured about the same .292-293

From everything I have found this is .004 to .005 thousandths under the sammi spec.

I tested a couple with a paint marker on the neck and got no major rubbing of the paint.

I did form a piece of 243 brass and it chambered very easy. the 308 brass chambers with slightly more drag on the bolt handle.

I assume that this means this brass should be good to go. I know this is not directly measuring the thickness of the neck brass so this is why I wanted to ask. Also this is not a competitive gun. I am just shooting around the farm and friendly competition with a few friends that shoot together.

Any help would be appreciated.
Thanks

 

[Mikecr]

I know this is not directly measuring the thickness of the neck brass so this is why I wanted to ask.

You said you measured necks at .292-293.
Doesn't seem out of place to me, (0.293-0.264)/2 = 14.5thou thick, which is slightly thicker than new 260 brass, due to downsizing. WHile you have clearance you can fire the brass & see what it springs back from chamber to.
What was your question again?

Why SAAMI would suggest .297 as standard is beyond any sense IMO. That would put neck thickness at 16.5 which is utterly unreal.

 

[bdcook]

I used a dial indicator and a round steel stud in a vice and used it to check thickness of the necks. My winchester 308 brass formed to 260 checked at .0135" to .0145"

This confirms the Math that was done earlier by Mikecr. I guess I am going to form the rest of the brass I bought (50 pieces) and load them up. Unless anyone sees any problem that I am overlooking?