yes i have played with this idea over a few weeks , what let me down is the total lack of any engineering tooling,
i brought to lengths of all from ebay for a tenner 40mm by 10mm cut then into five 100mm long pieces, marked one side one two pieces with a sharpe pen and flatted that side on some 800 wet and dry on a plate of glass.
step two, clamp both pieces to teghet and drill two holes 5mm in diam on in each corner and fit a roll pin into it as a guide to posisioning them together
so we now have some thing that is split and can be replaced together again, slap the two plates together and in a piller drill with a 3mm drill bit bosh out a series of holes say 15mm apart on centres each hole 4mm deep.
clean out the swarf and redrill the holes with a propper 5.5mm drill, propper as in NOT from screw fix or b&Q but a propper metal engineers shop that sells drill bits by the 0.1mm not the half inch nails b and q do.
the first lot i did were 5.5mm round and 7mm long, these were then filled with lead and then we realised we had not flatted the top off, so we redid every thing and started again, once cooled the lead waste is cut but sliding a stanley knief blade from one end to the other we now have a load of full 5.5mm holes with a smoth flat top, i then twisted by hand a counter sinker into each one to make a skirt.
what i ended up with were pellets that went to well over 12ftlb when shot through a standard 12 ftbl rifle this is due to the extra weight they were , extremly heavy, i needed to drill out more lead
other points, try to ream the holes from 5.3mm to the finish of 5.5mm it makes a cleaner pellet and if you want you can increase to 5.51mm up to 5.57mm to find the size of your barrel.
secondly use a milling machine or again propper drill press , home hobby ones wobble to much on such a small depth hole
other problems were just down to basic metal work skills being dog rough and not having the tools acurrate enough to work past point of a mm
someone did offer to make me a propper pellet making machine stamp press. i though the grand he wanted was well worth it , the down size was that you needed to feed it diamentionaly perfect lead rounds that weigh to the nearest grain, neither of which i can do at an allotment shed
i also tried cutting lengths of plumbers solder and hammering it into an alli mould and trimming off the flash, again the pellets can be made but were i could not get any where was consistant accurasey on pellet shape and weights.
i did once fire a .22 bullet for a 0.22LR round mould, through an air rifle. these are very easy to get hold of from the states. it did work and it did release from the barrel but i was glad it was not mine as the kick when it left the barrel was bad, a lot of over pressuer and struggle going one for such a heavy weight.
the idea world would mean finding someone that can machine the pellet profile it a piece of alli or prefferable stainless so you can cast the lead into it and then ram or die press the mould to confirm the pellet shape.
pete