The Gun Pimp wrote:Well, a 308 mandrel - in theory - would give you no neck-tension as it is the same diameter as your bullet but, of course brass is a little springy so the 308 might do. If you want to increase neck-tension go a thou or two smaller. Lightly lube the inside of the necks before you upsize. I mainly shoot 6mm and I have 3 or 4 mandrels.
IME, the Sinclair E30 mandrel (you also need a mandrel die body to hold it in the press), as in:
https://www.1967spud.com/shop/sinclair/ ... -die-body/
https://www.1967spud.com/shop/sinclair/ ... rsized-30/
as examples work perfectly with cases whose neck O/Ds have been sized down to 0.003" below that of the smallest loaded round.
I have a collection of these Sinclair 'E' mandrels from 22 to 30 calibres, originally bought for use on cases before neck-turning, but I found that they provide the degree of neck tension I like on every cartridge I've used them on. So, I only rarely use the expander ball on any sizing die and expand as a separate step. Being steel mandrels, it is essential to lubricate the inside of the case-neck well or the mandrel quickly galls and picks up brass flakes. Dry powder neck lubes have never worked for me and Q tips plus Redding / Imperial die wax are used and then cleaned off afterwards - tedious, but this process gives very consistent results and is very easy on brass.
Although what the Gun Pimp says about use of bushing dies on non-turned cases is in general correct, the 'Type S' has an expander ball fitted as standard for that very reason and as I said in my earlier post, the correct bushing size is the one that just sees the expander ball work on the reverse press stroke. The only 'Type S' I have is for 308 Win and I very rarely use, really only for switching cases between rifles / chambers. My usual 308 sizer is the Forster Bushing-Bump die plus the E30 mandrel. The 'Bushing-Bump' model is a bushing neck sizer without expander, but where the die body contacts the case shoulders and 'bumps' them to a constant setting. The case walls underneath remain untouched, but in a minimum SAAMI type chamber and with good brass, they never need to be as long as they're fired in the one chamber. (Neck sizing alone isn't a good idea as the shoulders move forwards, and inconsistently at that between cases, so that with anything other than light loads loads soon cause hard chambering due to 'negative headspace' or in plain English ending up as a crush fit in the chamber.)
When I bought the 'Type S' die, I also invested in Redding's optional (and expensive) carbide expander ball which reduces friction further. Even with that I lube neck walls. With everything set just right, I only barely feel the thinner cases pass over the ball on the reverse stroke on a very sensitive Forster Co-Ax press with the optional short handle fitted. Thicker wall cases (whose inside diameter is smaller after the sizing action) provide a little more resistance.
As the 'Type S' die uses a loose fitting 'floating' expander, the combination of minimum sizing due to bushing choice, hardly any expansion, and low friction / stress expansion thanks to the 'floating' carbide 'button' in a well-lubed case gives very good results and low neck runouts with quality brass such as Lapua, Peterson, and Norma out of the box.
Out of the box Lapua 308 Win brass will usually see a 0.0015" variation between the smallest and largest individual readings across the sample when measured at three places on each neck. Within an individual case, the three readings taken around the neck at the same depth will normally vary between nil and 0.001", or just below that figure. Most see a half thou' variance around the neck. A few other makes are as good, many much worse.