Same question was posed on this discussion thread -
https://www.thehighroad.org/index.p...bullets-versus-plain-lead-at-distance.819423/
From the discussion, general consensus was that for average shooters, not much difference was seen at 25 yards but noticeable at 50 yards and none of the top bullseye match shooters were using coated lead bullets (They use JHP bullets).
Properly sized and lubed lead bullets producing greater accuracy than inconsistently coated lead bullets is understandable as coating simply act as lubricant allowing gas leakage while lead lube under pressure acts as lubricant and also as "O-ring" to seal high pressure gas and "flow" to seal small gaps between bullet and barrel surface to produce more consistent chamber pressures which translates to more consistent muzzle velocities/smaller SD numbers which likely will lead to smaller groups on target.
This was my reply post to that discussion thread -
https://www.thehighroad.org/index.p...-lead-at-distance.819423/page-2#post-10514751
"As to lubed lead vs coated, I think what Glen Fryxell discussed in chapter 5 of his book is pertinent to our discussion -
http://www.lasc.us/Fryxell_Book_Chapter_5_Lubrication.htm
Coating on lead bullets simply act as a lubricant which allows gas leakage around the bullet while lube can act as both lubricant and "O-ring" sealant to better trap/reduce gas leakage to produce more consistent chamber pressures and greater accuracy.
'The fluid dynamics of lube flow has many components: simple displacement, compressive pumping, linear acceleration, radial acceleration, and pressure-induced pumping.
When the bullet is engraved, the lands displace not only bullet metal in the driving bands of the cast bullet, but they also displace a certain volume of lube in the lube grooves. This displacement serves to compress the lube somewhat, thereby forcing it into contact with the rest of the bore, as well as into the nooks and crannies of the bullet/bore interface.
This is the first and simplest lube pumping mechanism. As the pressure builds, the force applied to the base of bullet may grow to the point that it surpasses the compressive strength of the alloy. At this point the central core of the bullet in the lube grooves is compressed, getting fatter and shorter, which in turn reduces the volume of the lube groove. Once again this compresses the lube within that groove and forces it to the bullet bore interface.'"