25 creedmoor neck tension help

[7mm]

Trying to determine which sizing die or neck bushing size to buy for my 25 cm.
Using alpha brass and a 21st century. 255 expander mandrel (actually its the black nitride turning arbor which is 2 thou under bullet diameter)
Right now with the Virgin alpha brass the mandrel just plops right into the case, while the .256 expander i also have will actually expand the neck but im not sure if I want to run 0.001 (or 0.0015 with spring back) yet. Maybe I will later once the rifle tells me what it likes.

But right now should I just go with the Virgin alpha brass neck tension the way it is? Seems like they are all pretty uniform but I don't have pin gauges and can't really trust my mitotoyo to that degree.

Also looking at the f class products 25 creedmoor sizing die in the 282 neck od for my sizer...is that going to be sufficient in giving me enough initial neck tension so I can then expand using the 2 thou mandrel? Or do I need to look at the SAC bushing die

 

[db2000]

Check out some of the other 25CM threads. It’s discussed in one of those I believe.

 

[4O6shootist]

So I initially bought alpha 25cm brass. Had same results, about 001 nk tension out the box, and found loaded neck diameter to be around 283-2835. I have a KRUD reamer that's a 291nk and longer freebore. I didn't want that much neck clearance, and switched to 6.5cm brass necked down and now have a loaded neck OD of 0.286: perfect for my chamber. Anyway........I found with my first few 25cm barrels using the 131 blackjack, it liked minimal neck tension around 0.0015 and used a 256 mandrel to set that. Now I'm running 135hyb and using my normal 0.0025-0.003 nk tension jumping them 30k with sub half moa accuracy. I typically run a 283Tin bushing to get my 3k nk tension. Beings your using a lot thinner neck brass, and plan to use a mandrel to set the necks at 0.0015nk tension, your going to want to use a 280 or 281 bushing. 282 MIGHT get yoh there but doubt the mandrel will be doing much work.

 

[PinesAndProjectiles]

Load a round. Measure neck diameter. Subtract .002” or whatever you want to run for neck tension and that’s your bushing size.

If you start neck turning, that will obviously change your numbers and you’ll have to do this again after neck sizing.