Using modern day technology, how could I create a gun (regardless of firing mechanism and ignore space constraints) that could fire a radioactive bullet (maximum size capped at a cubic meters) which would produce a mushroom cloud (must be visible to naked eyes from an aircraft at 15,000m altitudes) upon impact? In short I need the smallest tactical nuclear sniper rifle in the world! (Battery not included but must support remote control function)

This question is inspired by a man who worked on Manhattan project, Louis Stolin. He discovered how to stabilize a plutonium bomb with a screwdriver, he adjusted the reflectors so that the plutonium never exceed subcritical mass. Unfortunately his hand slipped and the rest is history... let's continue his legacy with the smallest nuclear weapon ever existed.

  • $\begingroup$ “cubic meters” is well within the size of cold war warheads. Why do you want to fire from a morter (canon) instead of a missle? $\endgroup$ – JDługosz Feb 7 '17 at 6:42
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    $\begingroup$ Your specs are contradictive. The smallest sniper rifle, firing cubic meter sized nuclear warheads doesn't work. But let me introduce Bertha to you: en.wikipedia.org/wiki/Big_Bertha_(howitzer) or the handy rocket launcher en.wikipedia.org/wiki/Rocket_launcher $\endgroup$ – Alexander von Wernherr Feb 7 '17 at 6:55
  • $\begingroup$ @Alexander von Wernerr: Maximum size CAPPED at 1m x 1m x 1m... $\endgroup$ – user6760 Feb 7 '17 at 6:58
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    $\begingroup$ Cubic meter sized weapons are... not sniper rifle rounds. The largest artillery rounds ever fired from a naval ship didn't get larger than 0.46m! $\endgroup$ – Cort Ammon Feb 7 '17 at 7:06
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    $\begingroup$ The reason for the down-votes and the "non seriousness" is because of the contradictory of your question. The smallest critical mass (without reflectors) I could find is still cannon sized and not sniper rifles sized. Unfortunately I haven't studied enough nuclear physics to speculate on how small it could become with reflectors; my guess is that whatever volume or mass you remove from the payload will be added back with the reflectors, so you will never get it down to the size of hand held firearms. $\endgroup$ – Mrkvička Feb 7 '17 at 9:54

It sounds like what you want is... a nuclear device. Your specs aren't all that unusual. From Wikipedia:

Eleven years later, implosion designs had advanced sufficiently that the 5-foot (1.5 m)-diameter sphere of Fat Man had been reduced to a 1-foot (0.30 m)-diameter cylinder 2 feet (0.61 m) long, the Swan device.

Swan devices are recorded as having an explosive capability of 15kT, which is the same as the Little Boy bomb dropped on Hiroshima.

Now if you wanted to actually fire this morter style, rather than giving it a rocket motor, you might have to worry about the ridiculous forces involved, but since we can put a GPS guided computer on board the M982 Excalibur artillery round, I bet we can make something work.

If you want to get smaller, you're going to run into a classification issue. The nuclear powers tend not to like to broadcast their miniaturization capabilities. However, Wikipedia's page on Suitcase Nukes points out that the US has at least one acknowledged small nuke:

The lightest nuclear warhead ever acknowledged to have been manufactured by the U.S. is the W54, which was used in both the Davy Crockett 120 mm recoilless rifle-launched warhead and the backpack-carried version called the Mk-54 SADM (Special Atomic Demolition Munition). The bare warhead package was an 11 in by 16 in (28 cm by 41 cm) cylinder that weighed 51 lbs (23 kg). It was, however, small enough to fit in a footlocker-sized container.

The W54 had a yield of maybe 10-20 tons, according to its Wikipedia article.

If you need something smaller than that, unfortunately, there is literally no more information available to the public. Your guess is as good as mine.

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  • $\begingroup$ Actually they explosion caused by Davy might be a little too puny from the sky... that's why the CUBIC SIZE limit is for! $\endgroup$ – user6760 Feb 7 '17 at 7:19
  • $\begingroup$ Then I suppose you could interpolate between a Davy Crocket and a Swan device to achieve your desired yield while staying below the stated dimension requirements. You still run into the issue that these devices are the best that could be produced by nuclear weapon designers who are literally paid to do this, and have access to all of the information. Copying existing devices is really the best you can do. $\endgroup$ – Cort Ammon Feb 7 '17 at 14:34

So, nuclear artillery is a thing. The 8-inch W33 warhead had a yield of up to 40kt, and the earlier 11-inch W9 warhead had a yield of 15kt. There are some smaller weapons as well, but they're in the sub-kiloton yield range. The Davy Crockett was a small warhead fired from a dedicated recoilless rifle system, with a yield of 10-20 tons (not kilotons), while the W48 was a 6-inch artillery shell with about a 72-ton yield. A later prototype 6-inch shell, the W82, had a design yield of about 2 kt, but was never built or tested.

The 6-inch shell is about as small-diameter a nuclear device has been built, and due to the required physics of the weapon, they actually wind up heavier, needing more plutonium, than larger-diameter weapons -- the W48 weighed over twice as much as the Davy Crockett shell. It's been theorized by at least one weapon designer that a 4-inch shell is possible, but no existing 4-inch weapon is known.

So if you want a modern-technology nuclear fission device fired from a gun, you're looking at an artillery round, not a sniper rifle.

Also, regarding visibility, remember that any nuclear detonation (even a small one) is going to open with an extremely bright, if not blinding, flash, which would be easily visible at 15,000 m. And the mushroom cloud from even the small Davy Crockett's 10t yield reached an altitude of 3350 m, which is plenty high enough to be visible from that altitude as well.

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If your story is a science fiction story set in an advanced enough future, the production and storage of antimatter may be achieved.

A matter-antimatter bomb small enough to be the payload of a rifle bullet could probably be loaded with microscopic amounts of antimatter to create an explosion of any size from a firecracker to the most powerful fusion bomb ever tested on Earth, depending on the mission.

Living in a world where one's enemies might have hired a sniper armed with such bullets would be frightening.

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