Best time to turn necks?

[64Rambler]

I'm making 7mm-08 AI from .308 SRP brass (I bought before Alpha came out with 7mm-08 SRP brass). I know I will have to turn the necks at some point early in the process. A simple sizing with a std 7mm-08 die to get brass for fire forming a few cases to get dies made gave me cases that fit for first firing, but then needed a couple thou turned down for 2nd and 3rd firing.
So knowing I'll need to turn necks, is it better to turn the virgin .308, then size down to 7mm? Size down then turn? Or size down, fire form then turn?
Thanks,
Scott

 

[243winxb]

Size down then turn? 7mm-08 AI from .308 SRP brass

Yes, before firing.

I would full length size the new brass. Standard die, no bushing die. Then run up on the appropriate size expander mandrel that matches the cutter mandrel then turn the necks to what ever thickness you prefer.
Size again either in full die or in a neck die with your choice of bushing

 

[Sniper338]

Speaking for myself only.

Id size the new brass, load and shoot to fireform. Then come back and do your brass prep.

For me there's no reason to prep anything when your gonna be blowing dimensions out fire forming.

Once fire formed... then go in, resize fl bushing. Clean up primer pockets, flash hole, trim to length, chamber, neck turn.

When you change shoulder angles from standard to AI it changes the neck cutter bit you need to use to trim a hair into the shoulder. Just makes no since tondo it before. At least that my opinion.

 

[ShaunBrady]

I'm in the 243winxb camp. Turn after the neck down operation, before firing, neck must be sized with a non bushing die before turning. Bushings like Tubb uses in his dies that include the shoulder would be the exception.

If you have a reamer print for your chamber or a fired case, check the chamber neck diameter and compare it to your formed case. For decent accuracy and velocity spread results, there needs to be at least 0.003" clearance because after necking down there will be over 0.0015" variation in some of the neck thicknesses.

If a reamer was selected with the intention of minimizing the working of neck turned brass, neck turning before the first firing was baked in at the start.

I'll use a bushing die for most of the neck down process. 0.006-0.008" steps leave less runout in the neck. The last step before turning needs to be a one piece die.

With neck down improved cases, I'll use the cutter angle for the fire formed case. If there is a false shoulder involved, a dummy chamber in a barrel stub really helps with finding the right combination of sizing die position and neck turning depth that leaves enough preload for good fire forming.

 

[Leeman]

I've done it both ways, turning after sizing down and before sizing down and it was far easier to turn before sizing down at .308. I can only presume that there was some stress imparted to the necks and it felt like I was fighting to get the case necks onto the turning mandrel after the expander mandrel, following the neck down in the sizing die. If you have a variety of expander mandrels it may be easier to turn after sizing down but I was limited to what came in the kit. Like you I had to size down initially to measure the loaded round and obtain a target measurement, then turned all at .308, sized down, which was easier as well because the necks were thinner and finally a skim turn to the final dimension. I would do it the same way again next time. This was down to .264 by the way.