Folks that own cz52's and handload have experimented with sabot cartridges
as there are readily availible componants to do so (.30sabot w/.224 bullet)
they arent AP by legal definition because they are not steel core or posess a steel penetrator. but because there are different levels of soft body armor
there are bullets that will go through them that are not considered AP.
High velocity and smallish bore diameter seem to be the key...example:
its much easier to stab an icepick through something than a bowie knife, as the icepick has a smaller frontal area. Level one armor such as made of woven layers of Ballistic nylon(viet nam era flak jackets that you see at army surplus stores) with stop low velocity bullets such as a 158gr RNL .
38 special and a .45acp 230FMJ...but 9mm/ .357 mag/41mag/.44mag all go through without hardly slowing down. the key is anything going over 900fps
will do the job. now the lowest Level of armor we commonly see is the so called "2A" that is worn under a shirt....(16 layers Kevlar)1400fps seems to be its theshhold
and it stops most common service pistol threats such as 9mm and .357,
but put those same two in a carbine and at close range they will go through.
the better Level 2 armor which has about 22 layers of Kevlar will stop a good amount of things a BG might use on you short of a carbine. its threash hold is at around 1600fps...which allows stoppage of common service type and magnum ammo from pistols and for the most part 9mm from a 16" barrel.
now there are pistols such as a old ruger blackhawk revolver chambered in .30US Carbine, 7.62x25 FMJ fired from cz52's and Tokarevs and the 5.7x28mm FN SS192 civilian Hollow Point....that due to the .30/.22 bullets driven at considerably over the 1600fps....will go right on through even though they are not specially constucted as "AP"
the next step up the armor chain is Level "3A" which is around 48 layers of kevlar....with a thresh hold of close to 1900fps this is a bulky vest even without trauma plates or ceramic anti rifle inserts...and is typically worn over your shirt rather than under. It stops most all common pistol and pistol rounds fired from a carbine lenth barrel.....30carbine from a pistol no longer works, 7.62x25 from a pistol no longer works....the 5.7x28mm Hollow point will just make it though at 15 yards or so(the 5.7AP round SS190 will punch this vest at 50 yards from a FN57 pistol and does have a steel insert)
of course any of these vests can be penetrated by rifle fire if they dont have the hard ceramic inserts which add 16 to 25 lbs in most cases.
As they say" there are no vests that cant be penetrated, yet no round that cant be stopped. you wear the level of armor to counter the threat you expect to face at that moment.....and too little armor against an unplanned for threat will result in your vest and you having a new hole in them.
here is what the 5.7 civilian hollow point will do to a L2
Now back to the sabot 9 and .45...I think most things like that have allready been tried and just not found to be of merit, or reliable with too lite a projectile. and flechettes have certainly been tried as a small arms projectile and millions spent to make it work......and it still seems the best place for them is in "beehive " artillery shells. as getting hit with just one flying finishing nail isnt a sure stopper.......several hundred from a 105mm is a different story