20mm antitank rifles with HEAT rounds?

[Glimmerman]

High-Tech (p. 170) mentions High-Explosive Antitank (HEAT) rounds which have minimum caliber 20mm and (10) armor divisor.

Did historical antitank rifles like Lahti L-39 or Type 97 have HEAT rounds available? Could they have those at TL7?

Howabout todays TL8 Anzio 20mm anti-materiel rifle - could it have HEAT rounds?

[Anthony]

HEAT rounds don't like rifles (they perform poorly if spun) and don't much benefit from high velocity; as a result, they're more common as rocket or recoilless munitions (see the bazooka and panzerfaust for early models).

[Glimmerman]

Originally Posted by Anthony

HEAT rounds don't like rifles (they perform poorly if spun) and don't much benefit from high velocity; as a result, they're more common as rocket or recoilless munitions (see the bazooka and panzerfaust for early models).

I see. Bazookas' backblasts need bigger sniper nest and shots are more easier to see. So 20mm sniper rifle with AP rounds works against armored cars, but not against tanks.

[sir_pudding]

Note that the 20mm antimaterial rifle is a thing with marginal military value. Currently there are really only three weapons in this class, and two of them are modular weapons that are more typically deployed in another configuration (and one of those is a direct copy of the other too).

I was in a convoy of trucks that was hit with a 12.7mm antimaterial rifle. We didn't initially even notice.

[The Colonel]

Originally Posted by clu2415

When you fire ammunition containing explosives out of a rifled barrel, you have to design the projectile with a thick shell to stand up to the stresses of spinning induced by the rifling. Higher the muzzle velocity, the faster the spin and the more shell you have to add, which eats into your space for explosives.

When you combine an already small diameter projectile with the need to thicken the projectile walls, you end up with a very small HEAT mechanism. I suspect that the two factors combined are enough to make it impractical.

Also, as someone has already said, spinning a HEAT round upsets the formation of the penetrating jet, so between very low calibre, thick walls and a spin, HEAT is a really poor choice for a 20mm rifle round.

Originally Posted by sir_pudding

The M1A1 doesn't need or use reactive armor and is probably not to be grouped in the less fortunate category...

Last I heard we weren't using ERA on the Challenger 2 either - although someone may have put some in one of the many upgrade kits that have been cooked up in recent years.

Originally Posted by sir_pudding

Note that the 20mm antimaterial rifle is a thing with marginal military value. Currently there are really only three weapons in this class, and two of them are modular weapons that are more typically deployed in another configuration (and one of those is a direct copy of the other too).

I was in a convoy of trucks that was hit with a 12.7mm antimaterial rifle. We didn't initially even notice.

IIRC one of the 20mm anti-armour rifles was actually designed for the very specific task of blinding an armoured gunsight on one or two models of enemy tank...

[Ulzgoroth]

As others have noted, small caliber high speed rounds and HEAT are a terrible combination.

Originally Posted by Glimmerman

I see. Bazookas' backblasts need bigger sniper nest and shots are more easier to see. So 20mm sniper rifle with AP rounds works against armored cars, but not against tanks.

By TL8 and probably even the latter parts of TL7, you could have a LAW with a confined-space safe countermass rather than a shooter-cooking backblast. Still probably going to be more obvious about what you're doing, though.

The WWII British PIAT anti-tank launcher took an interesting alternate approach - it was spring-loaded. No backblast, no flash, and not much noise. Of course, you don't get a lot of range that way.

As for what a 20mm rifle can do, it depends on what tank, what angle you can get, and how close you can shoot from. A good 20mm AP round probably could penetrate most WWII medium tanks if fired into the sides at close range, almost all of them if fired into the lower sides (behind the treads) which were sometimes flatter and thinner on the better-protected machines, and could probably penetrate any operational tank in the war if fired down from above into the rear deck. That last, obviously, is rather hard to arrange...

EDIT: It's probably not going to do anything to any MBT that a regular-caliber rifle wouldn't do just as well. You could rattle the hull a little bit or try to snipe unbuttoned crew, but trying to penetrate is a waste of time.

[johndallman]

Originally Posted by Ulzgoroth

The WWII British PIAT anti-tank launcher took an interesting alternate approach - it was spring-loaded. No backblast, no flash, and not much noise. Of course, you don't get a lot of range that way.

There was a propelling charge in the base of the projectile. The spring basically just got it far enough from the operator that he wouldn't be hurt when it went off. It was a "spigot mortar" rather than a spring-gun.

[Ulzgoroth]

Originally Posted by johndallman

There was a propelling charge in the base of the projectile. The spring basically just got it far enough from the operator that he wouldn't be hurt when it went off. It was a "spigot mortar" rather than a spring-gun.

You're right, the spring wasn't the propulsion...but I don't see your attributed role attested. It looks like the spring was just a (rather oddly heavy) firing pin mechanism.

(In a spigot mortar, the propelling charge is fired while attached to the launcher almost exactly like an ordinary gun mechanism, except that the tube is part of the round instead of being part of the launcher.)

[Anthony]

Originally Posted by Ulzgoroth

By TL8 and probably even the latter parts of TL7, you could have a LAW with a confined-space safe countermass rather than a shooter-cooking backblast.

You only need it recoilless if the round is heavy enough to cause a problem. While I'm not finding a HEAT grenade at the moment, the M443 HEDP grenade exists (though it seems to have safety issues) and can be fired from an M203 grenade launcher. Not that 2" penetration in RHA will do much to a current tank, but it's still the equivalent of about 8d(5) in GURPS.

[Fred Brackin]

Originally Posted by Anthony

. Not that 2" penetration in RHA will do much to a current tank, but it's still the equivalent of about 8d(5) in GURPS.

DR 140 on _frontal_ armor in modern tanks may be unknown but most armor on all other facings is lower than that. See the T-72 in High Tech among others.