Right.  I read that the Swedish SLAP in their 762 DMRs had an average of 33% worse accuracy than standard ammo.  

 And that was recent too,  So it suggests bugs still haven't been ironed out.  Although those were 5mm bullets not darts

Also have any tanks used APDS with non-flechette projectiles?  We're they accurate..? 

smg762 said...

 And that was recent too,  So it suggests bugs still haven't been ironed out.  Although those were 5mm bullets not darts

Tolerances and aerodynamics don’t scale the same way caliber does, so I wouldn’t read too much into how a small-arms projectile behaves relative to a tank gun.

smg762 said...

Also have any tanks used APDS with non-flechette projectiles?  We're they accurate..? 

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.

Also I read that the ACR rifles used puller Sabots,  with someone opining that a cup or spindle sabot would have been more accurate.  

Historically virtually no one has achieved accuracy with regular projectiles- only with flechettes (in tanks). 

Logically then it would seem a small arm attempt should use flechettes. 

I am afraid, the opposite is true.

The U.S. 5.8 mm XM645 flechettes (BRL Report 1810 of 1975) had a standard deviation of about 1 mil, which is roughly 10 times the dispersion of an ordinary spin stabilized small arms bullet (0.1 mils standard deviation). Maybe, more modern designs have reduced this to 5 times the dispersion.     

No I meant that the only times sabots have achieved great accuracy is with flechettes (in tank)

Sabots With bullets have never had. Good accuracy. 

Therefore perhaps the only hope for small arms sabots... is flechettes 

The U.S. xm flechettes were obviously very old.  I still maintain that emulating the spindle sabot of a tank is the solution.  It would mean a long round.  You wouldn't want to match the l/d ratio of current U.S. tank flechettes.... they are comically long.  Other countries use far shorter penetrators

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.