will i be out of the "donut" region?

[bsumoba]

Based on my reamer print and my CBTO measurements, for my loaded 284 Shehane rounds, I got about 2.303" +/- 0.002" on the 20 rounds I am going to fireform and do the so called "break-in" barrel procedure (even though i dont really do it and do my own method). FYI, I am very happy with the whidden dies as I am getting 1 thou or less runout and these have an OAL of approximately 3.20" and are pointed 180 hybrids with 6.5x284 brass, necked with sinclair 7mm mandrel, then ran through the whidden 284 shehane dies. no neck turn...

Now, based on my reamer print (I did not measure my actual chamber just yet as I am waiting for it to be completed this month), but theoretically, if I am reading this correct, my rounds would have a 0.070" jump correct? So If I wanted to start with a 20 thou jump, I would have to load it out to 2.35" correct? Yes, I am assuming my distance from the base to lands is 2.370".

and if this is true, then based on my other measurements, a 20 thou jump will put my bullet outside the donut region. just wondering why a lot of guys are going with longer throats in the 0.200+" range.

 

[BradY]

I have a 284 shehane reamer that has a .318 neck and .220 freebore. With 180gr VLD's I can feel the projectile seating into the 'donut' area if I jump them. Jamming is fine. Hybrids jumped are fine as well. I just get around it by sizing the top half of the neck only so the donut stays wider than the bullet diameter. Alan Fraser, the 2014 National F Class Champion here in Aus (and also the 2nd day aggregate winner and member of our winning team at the 2013 FCWC loads the same way. Credit to him for sharing it with me (and others) as it seems to work well.

 

[Alex Wheeler]

I don't think you will have luck working off of the print. Forget the donut area, if your close to it your way too deep. The reason alot of guy are going to .220 for the hybrid is to keep the pressure ring in the sized part of the neck. Take a mic and measure the shank of the bullet by the ogive, then measure it over the boat tail to shank junction. You'll probably find a .0003-.0005" pressure ring at the junction of the boat tail. That pressure ring acts like an expander as you seat the bullet. If that pressure ring goes deeper than the sized part of the neck you will lose neck tension and the bushing you use will be irreverent. That is a serious problem. Since you are using a Whidden die your problem is even worse as that die does not size much of the neck. I went to a .225 fb and had the bushing pocket in the die deepened .030" with a carbide end mill. If you use an arbor press you will feel this happening, as you seat the bullet it will all of a sudden pop in towards the end. If the bullets you have do not have a pressure ring then you will be ok seating past the sized part of the neck.