Me, fireform/case design...... for BIG bullets. Liddle soup can shaped BR bullets will tolerate lots of slop. VLD's will not.
#1, a HEAVY crush fit, it needs to resist at least 50ftlb. So heavy that I must heel the bolt closed using both hands and my palm in most cases. GREASE those bolt lugs.
#2, .010/inch body taper and 35 degree shoulder. This can vary but I consider these #s to be optimal.
#3, .030-.060 radius at N/S junction. I'd go to a knife edge but I can't get my reamer guy to do it
#4, .0005 to .001 sizing effect at shoulder and .002-.003 at base (.200)
#5, .001-.002 total radial clearance on neck and .005 to .010 gapspace......
#5, I design my reamers from the lot of cases chosen and make chambers shorter than the shortest possible case, WITH the shoulders reset for crush and the ugly crinkle taken off the casemouth. I believe that the casemouth is the first muzzle the bullet sees and I feel cases must be as perfect as physically possible. therefor all of my designs are shorter/smaller than the parent case. I try never to blow a shoulder forward because it's too bloody much work. In many cases where I'm blowing shoulders out wider I must make a fireform chamber with a longer neck...and here it must be stated that fireforming weighs heavily into my choice of parent VS final case. In a perfect world they're all as easy as the 6PPC but really there are very few that well planned. One that's even BETTER than the 6PPC though is the 6X47L as mfgd from 6.5X47L brass. It's as beautiful as the original DAsher (the 22 one, not the 6mm corruption) I got the idea from the Dan Dowling/Al Ashton design, the ORIGINAL design, not the later bastardization....And it shortens so little that it really doesn't need a separate FF chamber...
These spec's are minimal.....you MUST know how to make, maintain and check these cases or they'll grow in length and crimp onto the bullet. Therefore, In my case I often am forced to buy a reamer for making a fireforming chamber, or I ream a neck out longer, or I spec so that my resize reamer has a long neck and works to make a FF chamber...
I make my butts wicked over-sized, like .005 to .007 bigger than the brass but this isn't a sizing issue per se.
Figure out a way to apply minimal lube to necks and lower half of body only, nothing on the shoulder.
NEVER let the sizing die touch down on the shellholder.
There's a lot goes into making cases last long, in fact only about 10-20% of the 6PPC BR guys can do it even with their access to perfect fireforming and maintenance tools but it is perfectly possible. Today I used a set of 338L cases that had been fired 20plus times in other guns to do the workup/tune on this gun. They've never been trimmed. And the bolt FALLS closed......There's so much involved that it's hard to cover all the details but suffice it to say IF YOU'RE TRIMMING EVERY 5-10 RELOADS...... you're not there.
Here's a pic I've posted many times.
These cases have over 75 firings on them now.....they had over 40 at time of pic. They still look the same.
If you're serious enough to actually go for it I can help you with each pitfall and I promise you it IS DOABLE.
Here's a link to an old thread about my 6X47L you might find some useful info.... if not, oh well, don't read
http://benchrest.com/archive/index.php/t-58805.html
hth
al
