I chambered a 30 cal heavy varmint barrel a few years back in a 308 win variant. I had a 30 BR reamer and decided to head space it as a 308. Asked Dave Kiff if it would work. He said yes and you would have less body taper and steeper shoulder angle, an improved 308 win but you will have to turn the necks to fit the chamber.
Why? I wanted a 308 but didn't want to buy the reamer.
I copied the neck thickness of the 30BR I had used in another barrel. Neck would be .0105" which would allow a bullet release of .001" per side.
The sizing was accomplished with a 30 BR RCBS FL die without the sizer ball. I thought that was pretty cool as all I had to do with the 308 is run it up into the die to wack the necks down for a .001" neck tension. If necessary the same die can be used to bump the body enough for easy bolt closure.
Now for the interesting part. I remember reading a wonderful article called the Secrets of the Houston Warehouse.
Secrets of the Houston Warehouse
In this article the shooter, Virgil, didn't size his fired brass! "With about .00035" clearance on all sides between the loaded round and chamber neck, the natural spring-back of the brass, in combination with his neck preparation, correctly gripped the bullets. Some other warehouse shooters, including T.J. Jackson, followed the same practice."
I noticed that my fired brass had a tiny bit of tension, enough that I couldn't push a 168 SMK back into the neck without some effort. I decided to deprime and load with NO case sizing. I single load so I didn't think .0005" neck tension would be an issue. The bullet also makes contact with the lands. I figure with this configuration I am soft seating and the bullet will move as bolt is closed to maintain consistent rifling engagement.
Bottom line? It shoots tight ragged holes at 100 yds just like it did with the previously neck sized brass with .001" neck tension.
I thought this would be an interesting find worth sharing. Imagine no case sizing! The lapua brass is on its 5th firing and the bolt still closes easily with no body bump.
Just had to share. Hope a few of you find this interesting.