okay I'm gonna ramble a little bit here and either muddy the XCB waters or clear them up some.
the original intent of the throat design was to have a bullet that was basically pre-slumped and glide through the throat under pressure.
this allowed every part of the boolit [can't help myself] to be supported somewhere somehow during the launch.
http://www.accuratemolds.com/bullet_detail.php?bullet=31-165A-D.png
take a very close look at this bullet.
notice anything about it that rcbs/lyman/lee molds don't have [except the ED Harris designed Lee which they promptly screwed up]
this is a bore aligning [not riding] boolit which demands exact sizing through proper casting and reloading techniques.
size it down .001 on the drive bands and you ruin it's chances at a good launch, or alignment. ['somebody' knew something about throat design when 'they' drew it up]
this is the boolit I push to 2400 in my 308 [10 twist] with accuracy [5 shot groups] using H-4831sc that makes most guy's at the range cry.
maybe I could get more but I'm good with the groups. [shrugging]
[shttp://
www.saami.org/pubresources/cc_drawings/Rifle/30-06%20Springfield.pdfhrug]
here is something else to look at.
the throat design for the XCB was taken directly from this drawing, except the neck diameter was supposed to be .003 smaller.
see that little angle right in front of the case/neck area?
that's the ball seat area.
how in the hell is a straight sided bullet supposed to deal with that?
oh... you just make them from lino-type and hope you don't get riveting to screw up the back of your boolit as it gets slammed right there by 50-k psi.
wonder why some powders don't work with a certain high bhn boolit?
yes, that is why.
now compare the first bullets picture with those angles, alignment galore, support you bet-ya.
ease of entrance without trailing edge failure and plenty of groove filling land gripping lead too. HMM
so you say you can't just take a mediocre design and make it bigger and hope it just glides right into this slightly [HA!] different throat shape and have it work.
http://www.saami.org/pubresources/cc_drawings/Rifle/35 Whelen.pdf
now here is a very accurate bore riding bullet.
http://www.midwayusa.com/product/15...ain-silhouette-gas-check?cm_vc=ProductFinding
you bet you want engraving on that nose.
picking and poking at the mold with different alloys will improve groups more than anything else you can do with the entire loading process.
that nose is what aligns the rest of the cartridge and ensures the boolit enters the barrel straight.
also that long nose is going to need support, and t is going to impart spin to the rest of the boolit following it into the barrel.
engraving is only caused by a diameter to diameter comparison.
this is avery accurate bullet if held to the 1900 fps or below area
and yes 28.5 grs of 4895 with a pinch of Dacron will make groups better/as good as the one above going 500-fps faster. [it will nearly do it with 18 grs of 2400 too]
if I use the right alloy for the fitment of the boolits nose.
how about something else?
http://www.midwayusa.com/product/11...rain-flat-nose-gas-check?cm_vc=ProductFinding
here is one of my all time favorites [it may have influenced the accurate mold]
it's a perfect feeding bullet in a 30-30 lever gun and fits the 30-30 throats pretty well too.
notice it has a crimp groove.
I have to put a firm roll crimp in there when I use it in my 30-30 leveruns or the bullet will stay behind when I de-chamber a round.
yep I believe in nose engraving.
but what about hunting?
that is my hunting bullet, I have shot everything from ground squirrels through deer with that boolit, same amount of engraving, same amount of alignment.
ohh one more thing I like about this boolit.
it has also gone to 2400 fps in a 1-12 twist barrel pushed along by a fast powder [AA-2230]
yes that is faster than a jacketed bullet in the 30-30 will go.
