JPeelen said:

XM645 flechettes

Most small-arms flechettes i have seen have stamped fins made on machines similar to ones making nails with similar precision,one wonders to what standard both the smoothbore barrel and the sabot was made to and its no suprise they are less accurate than traditional bullets.

given that a 17 cal bullet could give sabot like performance,  perhaps you could design more of a simple 'sheath' to prevent barrel wear. Fouling is a far bigger problem though. 

They also experimented with a 4. 32 bullet in a sabot.  Accuracy sucked so they tried to just use a regular 17 Remington... but barrel wear was bad. 

The project was called the  serial bullet rifle and AAI made a prototype. 

Google 4. 32 sabot and there's a bunch of old articles on 'Google books'

RovingPedant said:

Usually fin-stabilised projectiles are defined APFSDS, so APDS usually describes the spin-stabilised version. Chieftain used it and was good for 1500m, so adequately so in that case. The early APDS used on the 6 and 17pdr guns had accuracy issues beyond a few hundred metres so it’s not a universal thing.

There are pictures from the india pakistan war s of battle between the centurion and patton tanks. Indian practice was to fire 3 rounds rapid with the range being increased 200 metres after each shot rather than use a ranging machinegun as this was deemed faster. There are a number of pictures with 2 or sometimes 3 neat holes in pattons about 2 feet above each other an on basically the same line. At around the 1200 tom 1600 metre ranges of these engagements the 20 pdr was only deviating from the aiming point in combat by 15 cm or less. 

As others have mentioned, there are a few things to consider.

One is about production issues. One mm for a 5 mm caliber dart means 20% but for a 100 mm dart the same 1 mm means 1%.

Moreover, most small arms use rifled barrels and have some sort of muzzle attachment, both of which have been found to interfere with darts - it's no coincidence that, except for some cases like the British 120 mm gun, most current tank guns use smooth bore guns without muzzle attachments.

Last but not least, fluid dynamics don't change linearly with dimensions - stuff like Reynolds number depend on absolute projectile dimensions, which means that things aren't as simple as scaling designs up or down, and what works for big guns won't necessarily work for small guns, and vice-versa.

renatohm said:

Last but not least, fluid dynamics don't change linearly with dimensions - stuff like Reynolds number depend on absolute projectile dimensions, which means that things aren't as simple as scaling designs up or down, and what works for big guns won't necessarily work for small guns, and vice-versa.

A good example is that in a 30 mm gun, the thermal losses amount for only ~8% of the total chemical energy, while in a 5.56 mm gun those same thermal losses account for more than 20% of the total chemical energy.

Obviously a dedicated sabot rifle wouldn't want a. 556 barrel. 

I often wonder what the ideal bore-to-projectile ratio would be.  

Assuming a 4mm projo,  your bore size could be as little as 6mm,  or as high as 11mm,  The latter of which would mirror the proportions of a tank gun. 

I noted that both the innaccurate Swiss DMR an also the ACR guns had projos that were too light.  The Swiss had 50grains yet the energies were in the 762nato range. 

I think a 53grain projo with 1000ft lbs is the sweet spot.  

21' barrel and no muzzle attachments. 

Ok, so what you're STILL MISSING is that tolerances don't scale in a linear manner and no amount of cargo culting "tank apfsds but smaller" can change that.

Another thing you're missing is that you need multiple orders of magnitude more small arms ammunition than you need of tank ammunition.

Tank apfsds is already quite spendy per shot as it is. If you just scale down the round linearly including the tolerance fixes you absolutely could make such projectiles and etc but they'd be substantially more expensive than even m995 or raufos.

Barring advances in manufacturing that allow an order of magnitude greater precision at an order of magnitude less cost it's just not going to work.

Hell, even if you magically got the things above you're still going to run into issues where your exactly miniaturized darts and sabots aren't actually going to be strong enough to fundamentally behave the same upon firing as a larger saboted tank apfsds.

Yes I long ago decided that the better route was a microcaliber rather than sabot. 

Still though a tank must be accurate to 3km,  while a good sabot rifle only 600m.   

Another argument is to only use sabots in the 762-level guns.  With vastly less ammo expenditure,  The tolerances can be better. 

Also imagine the litter problem if sabots reached 556-levels of usage. 

Make 'em out of compressed fertilizer with a seed embedded in each 'petal'  grow  flowers on the site of every battle. 

I am so confused as this conversation swerves like someone three times over the legal limit lol.