The .224 Clark is one of those wildcats with damn the torpedoes attitude.  
Way overbore, way misunderstood, and way forgotten the Clark never quite
died.  It lives on through modern iterations, the .224 Texas Trophy Hunter
and .22-6mm AI being two well-known descendants.  Pacific Tool still catalogs
the reamer and RCBS and Redding offer the dies.  But beyond these last
bastions the .224 is an underground endeavor.  One article by Layne Simpson
in the 1970’s and inclusion in “Cartridges of The World” caps its resume.  Ask
anyone about pushing heavy 22’s with big charges of slow powder and you’ll
probably get one of two responses (or maybe both).  Those tired lines include
“you must like terrorizing barrels” or “why go to the trouble when you can
build a 6?”  Unless you’re a chronograph junkie the .224 Clark doesn’t exactly
sell itself.  I hope to change that and will revisit this giant 22 using newer
powders and bullets.  Barrel selection has also come a long way since it
emerged from the golden era of speed; especially with respect to twist rate
and durability.  This project will also force us to take a hard look at barrel

Kenneth Clark of Madera, CA designed this lightning bolt in the 1950’s.  
Presumably it was his rebuttal to Northern California’s windy hill country.  Out
there 400 to 500 yard open air shots weren’t uncommon on game.  Those vast
spans commanded flat trajectory and drift bucking ability and at the time Ken
wasn’t warm on commercial chamberings.   An unabashed tinkerer, he
decided to build a better mouse trap.
Clark’s work with long range small bores began as an assault on wind shortly
after WWII.  He first cut and necked a .300 H&H Magnum to .264, improving
the body and retaining the belt (sounds familiar doesn’t it?)   Quality 6.5
bullets were in short supply and follow-through on targets was tough under
recoil.  Nevertheless his .264 spun 120 grain spire points to 3,400 fps and 150’s
to 3,100.  It had a leg up on the relatively new .270 and could’ve influenced
Winchester’s .264.  But Clark wanted less bore and went on to test .228 caliber
using .30-06 brass.  Speeds were lazy, especially custom 125 grainers at
2,800.  Disappointing as that may have been the real rub was fitful accuracy.  
Key-holing and shifting POIs plagued the big .228.  125 gr pills were simply
overweight for caliber and no amount of twist settled them.  Why he didn’t
move to 90 or 100 grs is unclear; it would’ve been the logical progression.

Concurrent to Clark’s wildcatting was the birth of the mainstream 6mm’s.  I
see no evidence of him trying that diameter but then again the history is
clouded.  We know the masses were treated to the .243 Winchester and 6mm
Remington in 1955.  I believe those would've achieved Clark’s objectives but
he stayed with his named designs.  Perhaps to gain velocity he next downsized
to centerfire 0.224”.  A second attempt with full length .30-06 was made and
like the .228 it struggled.  Powder burned inefficiently, giving mediocre
performance at normal pressures or unsafe spikes at targeted speeds.  Even
worse, the bullets were shedding their jackets when pushed hard.
Heavy, high sectional density 22’s met Clark’s ballistic prerequisites.  Of
course the end-game wasn’t to find the idyllic wind beater.  Recoil and barrel
life had to be considered when matching weight, powder characteristics,
volume, and twist.  Ken started with the projectile by forming thick jacketed
80 and 85 grain bullets in .224”.  They showed promise but two questions still
lingered.  How big a boiler room and what should fuel that furnace?  Equally
important was the propellant's burn rate.  It had to be slow and dense.  In the
late 50’s two factory powders were a viable, IMR 4831 and H870.   
Consistency notwithstanding, military surplus powders like 5010 and 570 were
also options. Case selection followed and was the product of reverse
engineering. Clark’s finish line was 3,500 fps with the 80 grain and he needed
a lot of burn to get there.  The much maligned 220 Swift was spacious at 47.1
grains of water capacity.  When improved to the 220 Rocket it jumped to
52.2.  Was that enough shove?  Possibly, but Ken played it safe and opted for
more.  But “more” had to be tempered.  As he found with the .30-06 trials
there’s a point of over-reach with 22-caliber.  Topping out on pressure before
achieving that hypothetical is something all wildcatters dread.  Therefore he
split the difference and tried the 7x57 Mauser.    
Capacity (water grains)
Brass Manufacturer
22-250 Remington
220 Swift
Winchester - new
220 Weatherby Rocket
Winchester - old
257 Roberts + P
7 x 57 Mauser
30-'06 Springfield
Almost immediately after reforming 7x57 Ken switched to the .257 Roberts.  
He felt there was a strength advantage in using Winchester’s +P and back
then there may have been.  The 7x57 dates to 1893 and case quality and
thickness were patchy early-on.  Nowadays there’s no argument to be had.  
The 7x57 is just as tough.  Final dimensions for the .224 Clark:
I should comment on our tainted pound of 5010.  It was discontinued in the
1990’s due to an odd and reduced shelf-life.  Both IMR and Hodgdon sold 5010
from unused (meaning unloaded) military surplus lots.  During war-time
production is understandably accelerated.  Since longevity wasn’t of prime
concern they shortened the nitrocellulose wash and prep.  This caused the
powder to decay prematurely, leading to odor emission and discoloration.  
Now all powders do this over time, it isn’t unique to 5010.  As the propellant
deteriorates it releases nitrogen oxide.  In the presence of water, or just plain
humidity, one of the by-products is nitric acid. Nitric acid gas is extremely
bitter smelling and it causes rust, corrosion, and browning as seen above.  
With 5010 the vapor generated can actually transverse the lids’ paper seal but
I back to the Clark.
Straightened sidewalls and 30-degree shoulder move capacity to 60.5 water
grains.  The brass I’ll discuss below is Remington and holds 1.5 grains more
than Win+P.  Make a mental note that charge weights must be tailored to the
brand.  We’ll be right at 100% load density and 60,000 PSI for maximums.  A
grain or two over-compressed and you’ll point pressure, especially with these
long bearing surfaces.
The fastest 22 twist available to Clark in the early 1960’s was Shilen’s 1:9”.  
Slower than ideal but just enough to stabilize his 80 – 85 grain bullets.  This
also predates the use of stainless steel in firearms.  Winchester was one of the
first to leverage the alloy with the 1959 - 1960 run of .264 Magnums.  In order
to match the receiver the barrels were plated with sintered iron so they could
be blued.  Their engineers claimed 10 – 15% erosion resistance over chrome
moly but the trade-off was higher cost (material and the plating process).  
Gross margin won out and in 1961 they reverted to 4140.  A further disservice
was done to the round when they chopped the 26” barrel.  Today we’re
fortunate to have a wide array of 22 twist rates, stainless contours, air gauged
and pre-lapped concentricity, and even cryogenically treated barrels.