Topic of the Month: March
2002
Shooting Sabots
The sabot has been around a very long
time. In fact, the word sabot, pronounced say-bo, was introduced into the English language
around 1607 and literally means "wooden shoe." A sabot is a sleeve (shoe) that
partially envelops a projectile or bullet and positions the bullet in the barrel to
prevent the escape of gases, around the bullet, when the cartridge is fired. The bullet
diameter is smaller than the barrel diameter to allow room for the sabot. When the sabot
is fired from the gun, the high speed of the sabot creates a large air drag on the surface
of the sabot, causing the fingers on the front of the sabot, to open outward, developing
an even greater drag on the sabot. The high drag pulls the sabot quickly away from the
bullet, allowing the bullet to continue downrange to the target. The lightweight sabot
quickly loses velocity and falls to the ground somewhere downrange while the bullet
continues on to the target.
Fig.1 – Spinning sabot leaves muzzle of firearm at high velocity.
Fig. 2 – The sabot and bullet separate downrange. Note extended fingers on sabot.
Most modern sabots, for
sporting gun use, are injection molded from heat resistant polycarbonate plastic or nylon.
These plastic compounds will resist temperatures up to 500 degrees Fahrenheit and are
formed in one piece, with a recess for the base of the bullet and four to six fluted
fingers at the front. The most popular sabot is the 22/30 sabot using a .22 diameter
bullet in a .30 caliber sabot. Sabots presently being marketed allow 22/30 and 30/50 sizes
and sizes of 22/243, 243/7mm, 22/270 and 243/270 are expected to be available in the
future.
Fig. 3 – Sabots and cast bullets for the .30 Herrett and .30 Carbine cartridges.
Remington has been producing
sporting ammunition loaded with .30 caliber sabots (containing .224, 55-gr. bullets) for
the .30-06, .308 Winchester and .30-30 for several years. They named this sabot-loaded
ammunition "Accelerators." This was an appropriate name, since this ammunition
produced velocities two to three times the normal velocity obtained from bullet-loaded
ammunition for these calibers. Remington reported a muzzle velocity of 4,080 fps for the
.30-06, 3,770 fps for the .308 and 3,400 fps for the .30-30. The idea behind the
"Accelerator" was to provide the hunter a practical means of taking small game
with a large caliber rifle, without destroying all the eatable meat. In effect, the hunter
was using high-speed .22 caliber bullets, fired from a standard .30 caliber rifle. This
worked particularly well when the hunter wanted to carry just one rifle. By carrying both
.30 caliber ammunition and sabot-loaded ammunition, the hunter had the equivalent of two
guns-in-one.
Fig.4 – Drawing of Remington .30-30 "Accelerator" cartridge.
Remington manufactured sabots only for
production of their "Accelerator" ammunition and did not release these sabots
for sale to the public. I managed to obtain a limited supply of Remington sabots from Blue
Star Cartridge & Brass Co. of Searcy Arkansas. Blue Star had managed to obtain several
55-gallon drums of 22/30 sabots (complete with bullets) from the Remington ammunition
manufacturing plant, near Little Rock, Arkansas, when Remington decided to stop
manufacture of accelerator ammunition. Recently, the introduction of inexpensive .30
caliber sabots, by J&D Components (www.jdcomponents.com) and others, has opened up a
new field of experimentation for the reloader.
The idea of handloading ammunition with
sabots offers many exciting possibilities that can't be achieved with bullet-loaded
ammunition. The muzzle velocity of the bullet is substantially increased due it’s
light weight, as compared to normal weight bullets, and less drag presented by the sabot
during travel down the barrel. Barrel life is greatly enhanced as the sabot resin material
has less frictional wear against the rifling. Also the barrel rifling does not have a
build up of copper or lead residues from bullets. Since the bullet is incased in the
sabot, while traveling down the rifle barrel, it never touches the barrel. This means the
bullet can be made entirely of soft material (or very hard material) and still be fired at
high velocity with none of the usual barrel problems associated with using soft or very
hard bullets materials at elevated velocity.
The military use sabots in their anti-tank
cannons to fire high velocity penetration projectiles at enemy tanks. These projectiles
are rod-shaped, constructed of either tungsten carbide or spent uranium fuel, and are
housed in a two-piece sabot. Upon firing, the sabot breaks apart, allowing the finned rod
to continue to the target. The high-velocity rod actually bores into and vaporizes its way
through the thick armor of the tank. Once it enters the interior of the tank, it breaks-up
into flying chunks of white-hot metal that wrecks havoc inside the tank. The sabot allows
the penetration rods to be fired at the required velocity (4,000 fps+) to penetrate the
tank walls.
The main problem the reloader faces when
loading sabots is the lack of good loading data. Some sabot manufacturers supply load data
with an order, if requested. None of the popular reloading manuals address sabot loads. I
was surprised to see that one sabot manufacturer supplied reloading information developed
from my "Load From a Disk For Windows"(LFDW) Internal Ballistics program, with
each order for sabots. Although I had never tried the ballistics program with sabots or
even had sabots in mind when I wrote the program, it was expected that reasonable results
could not be obtained with this program for rifle data. The program works so well with
most rifle "wildcat" cartridges, why not with sabot loads?
My interest in the .30 caliber sabots was
centered on using these sabots in handgun cartridges such as the .30 Carbine and .30
Herrett, loaded with cast bullets. The results of the tests with these cartridges can be
found in an article that I wrote for HANDLOADER’S DIGEST, No. 16 entitled
"Sabots in Handguns." Most of this testing was done with the RCBS #225055 GC
55-gr. cast bullet and the Lyman #225462 GC 53-gr. cast bullet.
I used Thompson/Center Contender handguns,
with 10-inch barrels, for both the .30 Carbine and .30 Herrett. I also had a 20-inch, .30
Herrett "Bullberry" barrel and rifle stock for the T/C Contender which was used
for comparison.
Seating bullets in a sabot requires a
different technique than most reloaders are familiar with and some of the sabot
manufacturers supply (at additional cost) a special two-piece seating die. This die has a
plastic sabot holder, shaped similar to a shell holder, and a bullet seater that looks
like a threaded 0.85 X 2.2-inch plastic rod with a 1/8-inch hole drilled through the
middle. The rod is screwed into the reloading press like a reloading die. The sabot holder
is snapped into the ram of the reloading press, replacing the conventional shell holder. A
sabot is inserted into the sabot holder and a bullet is inserted into the mouth of the
sabot. The loading press ram is slowly raised until the tip of the bullet enters the
center hole of the seating rod. Raising the loading press ram further, centers the bullet
and pushes the bullet into the sabot. Screwing the seating rod up or down in the loading
press controls bullet-seating depth. All bullets must be seated to the bottom of the
sabot.
Fig. 5 – Two piece seating die for seating bullets in a sabot.
Most of the early testing was
done at 10 to 25 yards, but sometimes this proved to be too close to get reliable
bullet-sabot separation before the bullet entered the target. Poor separation was easily
spotted from the target group. If the target hole was larger than the bullet or a
star-shaped hole appeared on the target, the sabot had not separated completely and fallen
away. The star or gear-shaped hole was produced when the sabot passed through the target
with the fingers extended. Increasing the target distance usually eliminated this problem.
Fig. 6 – Target showing expanded sabot hole as it followed bullet through target.
Also shown is a recovered sabot.
I found that a muzzle velocity below 1,200
fps would not always provide reliable separation of the sabot. Muzzle velocities above
1,800 to 2,000 fps usually gave good separation. Bullet style also seemed to affect the
minimum velocity of separation. Bullets must be seated to the bottom of the sabot. An air
space at the bottom of the sabot allows perforation of the sabot base with unpredictable
results.
Maximum velocity for the .30 Herrett was
2,893 fps in the 10-inch barrel T/C and 3,193 fps from the 20-inch barrel
"Bullberry." Maximum velocity for the .30 Carbine was 2,496 fps in the 10-inch
barrel T/C. Soft lead bullets performed very well at velocities up to 3,000 fps and
beyond. Firing sabots with soft lead bullets into a thick telephone book tested bullet
expansion. These bullets were recovered and measured. It wasn't unusual to find .22 cal
bullets expanded to about the size of a dime. The expansion qualities of these bullets
should perform well on small game. If you are looking for something new and challenging,
then handloading and experimenting with sabots may provide a whole new adventure for you.
It's a new and exciting experience and you can be assured you are working on the cutting
edge of technology.
Watch our web site for the next topic of
interest "Temperature Effect on Ammunition." Until then, shoot safely and know
where your bullets are going.
Sincerely,
The Ballistician
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