Dispersion?

Yesterday was a rare Nov. day in Michigan..79 deg. and very light to calm wind..just had to take advantage and go shoot!  I usually have shot my Sharps Borchardt , Shillen barreled .22 Hornet at 100yds using cast..but decided to try it out at 50yds.  I remember thinking at this short range they should all group into 1 ragged hole.  Boy were my eyes opened.  My average group with cast in this rifle at 100yds is around 3/4" to 1"  Sometimes..(nearly 20 years ago) when I first started working with it I could get 1/2" to 5/8" but not every time.  I had the late Fred Leeth make up nose pour moulds in both gas check & plain base of same weight..based on the old Ideal 22636 design.  These have prooved to be very accurate.  I have a dbl. cav. Lyman 225415, which I hardly used because of the custom moulds..but this one really surprised me giving some smaller groups than the more expensive moulds.  I also tried the little early Ideal 225415..the 48gr. g.c.  This gave me 1/2" groups using 7.0grs. H4227.  About those 50yd. groups..instead of 1 ragged hole as I thought..I was getting 1/2" to 7/16"  a bit smaller than 100yds. but not that much. The 1 big improvement in accuracy came when I swagged a 3 deg. taper on 1st. band to match chamber leade angle & chamber so to contact or even engrave this band as action closed.  Try as I might..and I am weighing bullets and powder to .1 gr. tolerance I cannot seen to get below 1/2"..and nearly always wit a flier.  The one bullet that possible could achieve this is an Eagan MX22..now when shot as cast it groups about like all the rest..but size it down to .225 or .224 & swage back up to .226 in a Corbin bullet swage die I had made for my reloading press..I had various shaped nose punches made up..swagged to a tapered flatnose..the bullet takes on a new look.  grease grooves are quite narrower (filled with Lyman Super Moly before swagging) the gas check is perfectly flat & corners sharpened up square..I leave a tiny rad. on bottom edge of check.  I shat a 1/2" group but with 4 cutting into 1 hole.  But why?  Pope insisted a bullet was as perfect as it was going to get right from the mould.. I really don't think I am closing up any voids inside bullet with the modest pressure I apply.  The base and sides are very much improved though.  Why can't I get results like this with my precision nose-pours?  Heck, even that dinky early 225415 48gr. shoots like this when run swagged.  Any ideas?  I also have used Pufflon ballistic filler and it improves some loads and others not so much..This stuff never seems to end!