From: [EMAIL PROTECTED]
<< < everyone I've spoken to says the Sierra bullet is best for
300m, it tolerates jump better than a VLD (or rather it does,
whereas a VLD doesn't) >>
The Sierra 69gn MatchKing was the .223 cal. bullet
that all others were judged by once upon a time, but
there are others that fill this role nowadays. Namely,
Hornady's 68 & 75gn match bullets, Sierra's 77gn, JLK's
77gn and Berger's 73gn LTB (length tolerant bullet) to
name the more popular bullets.
The Sierra 69gn and Hornady 68gn bullets are very good,
if you are limited to a maximum of a 1-9" or 1-10" twist
barrel. If you have a faster twist such as a 1-7" or 1-8"
twist, you'll probably be better off with one of the heavier
bullets.
What all these bullets have in common is that they were
all designed to be loaded to a max length of 2.260" which
is the maximum length for a AR15 magazine.
This means that a 5.56 chamber will have about .120" of
freebore but in a .223 chamber the freebore is only
around .025". Therefore this is the reason
that .223 chambers are more accurate.
>>Bullets usually jump from the case mouth into the rifling,
unless you handload very carefully, that is why (as far
as I am aware) there are no factory made VLD loads, because
the ogive of a VLD is what gives it "very low drag" but
also makes it less tolerant of the jump.<<
VLD's such as Berger and JLK 80gn bullet's have what is
called a J4 jacket which is very thin and it is critical
to set these up with something like only .010" of jump
to the lands or seat them so that they are actually
touching the rifling or even seated into it. Each rifle
is different and you really do have to test to get the
best load for your individual gun.Therefore it is unfeasible
to offer these as factory loads with the differences in
chamber dimensions and liability laws with relation to
overly high pressures and the accidents that could result
from this.Sierra MatchKings have a thicker jacket and a
more tolerant to bullet jump.
>>What organisations like the USAMU do to save on handloading
time is to tailor the rifle to a factory load like
Federal Gold Medal, so that there is no jump but they
can buy ammo in bulk. <<
Not true. What they do is buy factory ammo such as Federal
Match because they shoot so much of it and they also have
over 200 rifles to load for. Also, the bullets do jump
because they are fed from the magazine and are used in the
rapid fire stages in Highpower competition at 200 & 300yds.
At 600yds, they all use 80gn bullets and these are not
designed to be magazine length but loaded out to touch or
sit just off the rifling which means that in a 5.56 chamber
the oal will be about 2.550" compared to 2.260". If you
load an 80gn bullet to mag length, it will severely limit
case capacity and because of the longer ogive, will jump
even further to the rifling.
>> Swiss Ammunition Enterprises have loaded 5.56mm for the
USMC including with an 80gr VLD to their specs for their
rifles (for 600 yard courses of fire), because the USMC
have a lot of identical match rifles with identical
chambers, so they can specify the OAL of the load that
they want quite precisely. I don't think anyone else
would be that fortunate!<<
I strongly doubt this. All the shooters in the USMC rifle
team handload their own 600yd ammo and also as the throats
in their rifles erode through use, their loads have to be
adjusted to keep up with the changes in oal.
USMC use the Sierra 80gn Matchking which is not a VLD in
the true sense but is a bit more forgiving when it comes
to bullet.
Mark Bradley
--
SM have loaded it for them, last time I was in Switzerland
with BAR everyone was trying to track some down, I think
Neil Saint knows a bit more about this one, but it does
exist. The USMC rifles wouldn't have much in the way of
throat erosion because they replace the barrels so often,
and as you point out the Sierra bullets have thicker
jackets anyway so it's not as critical as with the VLDs.
