Target Sports

SPORTS STARS: SABOTS

Created on 18th May 2009

LAURIE HOLLAND investigates sub-calibre supersonic sleeves

A COUPLE of issues ago reader Bozidar Zabavnik proposed using sub-calibre sabot ammunition to produce high velocities but restrict ultimate ranges. Unfortunately, there is no free lunch in ballistics. Reach would be constrained alright, but at the expense of performance at any reasonable distances (which is why F-Class shooters use 6.5-284 Norma and not .22-250 Remington). However, sabots see use in some sporting and military applications. A sabot is a bore-sealing sleeve that fits around the projectile and is discarded immediately after leaving the muzzle by being forced open and off the bullet or shell by air resistance. Sporting examples employ a one-piece elastomer cup, the (open) front end of which is tapered and slotted to give ‘petals'. Remington alone produced such sporting rifle cartridges with its short-lived .30-30, .308 and .30-06 Accelerators, all employing a 0.224" diameter 55gn JSP ‘varmint' bullet in a nylon sabot for MVs of 3,400, 3,770 and 4,080fps respectively. The intention was to give deer rifles a coyote and ‘chuck' shooting capability. It did work as intended, albeit not as well as .22 centrefires in ‘varmint rifles'.

Muzzle-loading

The sabot is still alive and well in muzzle-loading ‘hunting rifles' as well as cartridges for that other uniquely American sporting phenomenon, rifled shotguns. The latter use conventional low-pressure brass-head, nylon body shotgun hulls loaded with solid slugs for shooting over land where conventional high-power deer rifles are banned on public safety grounds. Sabots allow longer, smaller-calibre and smooth-bodied (hence more ballistically efficient) projectiles at higher velocities (1,900fps in 12-bore), doubling the effective range of both types compared to their use with conventional muzzle-loading bullets and shotgun slugs.

Armour-piercing

Sabots provide increased velocities through increasing the area for powder gases to work on for any given calibre and bullet weight. As an example of how this works, look at the .308 Winchester and its .243", .260", 7mm, and 0.358" offspring. The last-named (.358 Winchester) is the most efficient as measured in ft/lb ME generated by each grain weight of charge. Each step down in calibre gives poorer results, so .243 Winchester and 100gn bullets produce 25% fewer ft/lb per grain. However, it's a different story once the bullet leaves the barrel: 225gn 0.358" calibre models are less aerodynamically efficient than lighter, smaller calibre bullets - making the cartridge a short-range number.

However, what if you obtain a large base area by using a big bore and matching sabot allied to an exceptionally long, small-calibre projectile - especially if you can increase its aerodynamic performance by using a dense metal to add weight? This is the military approach, a smaller-calibre example being the 1980s' US M903 SLAP .50BMG. A plastic saboted 440gn 0.3" calibre projectile boosted MV to 4,920fps, trebled effective range, and enhanced armour penetration greatly. However, like most early ultra high-performance projectiles it used expensive, hard-to-machine tungsten. The material of choice is depleted uranium (DU) nowadays - that's what is left over from the uranium enrichment process after the fissile U235 has been extracted from refined ore. It's nearly twice as heavy as lead, readily available, and easily worked. There are thousands of DU drums in storage as there are few other uses and it's radioactive. Sabots plus DU make for the ultimate ‘target cartridges': 105 and 120mm tank-cannon shells that had a two-piece aluminium (now carbon-epoxy composite) dumbbell-shaped sabot encasing a two-foot long DU dart. Weighing 9.41lb, despite a mere 1.06" (26mm) diameter, sectional density is 8.37 (over 30 times greater than that of a 180gn 0.308" calibre rifle bullet). With a similarly enhanced BC and the 120mm gun producing over 5,000fps MV, external and terminal ballistics results are frightening, with a point-blank range of 1,000m-plus and flight-time well under a second to that distance.

Laser sights and computerised fire-control equipment allow hits on tank-size targets up to 3km - and they're moving, putting this shooting into a different range and accuracy category from ours. At the receiving end, DU penetrators have barely slowed and burn through any tank armour producing 1,100ºC-plus temperatures (not to mention the horrific effects on the unfortunate crew-members, whose demise is mercifully usually instantaneous). There are also allegations that ‘Desert Storm' hits produced toxic/radioactive dust which may have been a factor in Gulf War Sickness and possibly caused cancers and birth defects in local populations. On reflection, I think I'll stick with Sierra MKs and Lapua Scenars!

SPORTS STARS: SABOTS

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SPORTS STARS: SABOTS

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