We finished the rifle in the fall of 2013.  Component & build details are
outlined below:
  • Action – 1931 Czech 24 action (Mauser 98 pattern)
  • Action Finish – Duracoat, stainless steel tone
  • Barrel – Stainless Shilen. Premium Select, 1:7 twist cut to 28.5”.
  • Barrel Contour – Light Varmint, Number 5
  • Magazine – converted to single-shot with an aluminum benchrest
    follower.  The bullets are too long for the well and capacity wasn’t a
    concern
  • Scope  - Nikon 6 to 18 X, 1/8 dot fine cross-hair
  • Scope Rings – Weaver Grand Slam
  • Scope Bases – Weaver 45 & 46
  • Stock – Richard’s Microfit, black & gray laminate
  • Trigger – Timney adjusted to 1.5 lbs
Fermin Garza, friend and fellow forum member, was generous enough to
send me the RCBS dies.  I also had Redding make a set for my dad in case he
builds a Clark.  They’re custom and run $150 - $180 with a 4 to 5 month wait.
Initial hi-perf loads were assembled with US 869 and Retumbo.  Each was
topped with Berger’s excellent very-low-drag (VLD) 90 grain boat tail.  These
bullets set sleek on its ear.  15 ogive pointed and with a 0.551 G1 ballistic
coefficient they’re damn close to wind defying.  Berger forms them with J4
jackets so wall consistency <= 0.0003”.  Perhaps they should include the
phrase “match grade” when packaging.  
A secant ogive is used to get the high ballistic coefficient.   Secant
transitioning lowers drag but makes the tune more sensitive to seating
depth.  That’s because the juncture to the bearing surface is more abrupt and
less self-aligning.  When introduced Berger said to seat on, or a couple of
thousandths into the lands.  That worked for some but in competition
improved accuracy was achieved through jump seating.  Some gapped them
0.150” while others fell between 0.020” and 0.050”.  Fortunately the windows
are pretty wide.  If you shoot VLDs start on the rifling, then re-seat in 0.040”
increments.  Stop when you attain the desired accuracy; don't exceed 0.150”.
I went with magnum primers because both Clark and Simpson endorsed big
spark.  Powder this slow usually benefits from hotter ignition so their advice
wasn’t a surprise.  Simpson’s experience was however.  Loaded with
standard large rifle he had to stop one grain before the magnum’s max.  
Pressure was spiking faster according to his micrometer.  All of the loads I’ll
discuss employ CCI 250’s.  The tale of the screens:  
Bullet
Powder
Charge Wt.
Velocity
Notes
Berger 90 gr VLD
US 869
57.0
3,482
Mild
Berger 90 gr VLD
US 869
59.0
3,567
Warm
Berger 90 gr VLD
US 869
60.0
3,611
1/2" @ 100 yards
Berger 90 gr VLD
Retumbo
57.5
3,498
Good accuracy
Berger 90 gr VLD
Retumbo
59.0
3,533
Better accuracy
Berger 90 gr VLD
Retumbo
60.0
3,564
3/4" @ 100 yards
Hornady 55 gr V-Max
US 869
63.5
4,307
For the hell of it
Hornady 55 gr V-Max
IMR 3031
30.0
3,128
Fire-form load
Overall cartridge length (OAL) is a widely cited metric.  While relevant for
magazines and feeding, it means very little to the accuracy crowd.  Bullet
curvature in relation to the lands does and for that reason I use ogive
inserts.  Here’s how they work.  

The point in which a bullet engages the rifling depends on its ogive.  By
definition ogive is the forward curved area between the tip and shank. That
curve is the segment of a circle with radius “r”.  Ogive denotes the number of
calibers required to equal that “r” value.   So a 7 ogive 6mm bullet has a
circular arc segment with r = 1.701” (7x 0.243”).
Since tip profiles vary between bullets you should never seat to a prescribed
length.  What matters is the distance from the back of the rim to where the
bullet meets the rifling.  In essence that becomes the starting point for your
tune.  Consider a 6 versus a 9 ogive 22 caliber.  The 6 has a less sweeping
arc segment and will touch the lands sooner than the 9.  If loaded to the
same OAL you’ll jump the hell out of the 9.  My dad made gauges to measure
this dimension.  Hornady offers something similar called the “Lock-And-Load”
kit.
The set-screw base attaches to any dial caliper and it holds caliber specific
collars.  Each insert is bored to the land diameter of the barrel, not groove.  
So on a 22-caliber the hole is 0.219”, 6mm is 0.236”, etc.  Once the die is set
and the bullet is on the rifling, measure the base-to-ogive length.  That’s your
touch spec.  My 90 grain Berger at the lands equals 3.07”.  If I wanted to
jump the bullet 0.020” I’d adjust the seating die until the gauge reads 3.05”.
Covering the .224 Clark without a section on ballistic coefficients would be
derelict.  The two are conjoined.   I won’t get into the math, it is involved.  In
the purest sense though a bullet’s ballistic coefficient (BC) measures its ability
to overcome air resistance during flight.  That measurement is done against a
standard projectile known as “G1”.  Unfortunately the G1 shape doesn’t mate
well with many of today’s aerodynamic boat tails.  This disparity accounts for
why modern bullets have bouncing BCs as velocity changes.  To their credit,
Sierra used to list multiple BCs depending on the speed.  

G7 coefficients are better approximates of modern low-drag bullets.  Unlike
G1s which are highly speed sensitive, G7s are more consistent across velocity
bands.  This permits direct comparison of BCs without having to consider the
bullets’ respective velocities.  For blunt, flat-based profiles G1 is still an
appropriate standard.
The 90 gr Bergers were really humping at over 3,600 fps.  Enough so that it
made me question my chronograph.  After that checked out I attributed the
velocity gain to the VLD shape and extra 2.5" of barrel (Clark and Simpson
used 26" lengths).  BTW, curiosity moved me to try the 55 grain V-Max.  It
jumped a lot of throat but held to 2 1/2" inches at 100.  How the jackets fare
at 4,300+ fps is unknown.