The CBA and other mags have had several write-ups on fins on bullet bases, both PB and checked. I have seen fins on gas checked bullets out of the 35 Rem before. I only get them with WW hard bullets being pushed hard in the 35 Rem though. The most interesting was a trial with moly coated bullets. Out of one batch, half were barely sized (oversize condition)and lubed and the other half were moly coated in as cast condition. These were loaded rather warmly and shot. The conventional lubed bullets had fins, the moly coated didn't. Seemingly, it has alot to do with bore friction. The lube has alot to do with alot of factors, I hope some group comes up and out with all of them someday.

Interesting observations...

OK-- consider these scenario's. Say I shooten a 14 bhn ww alloy slug at say 35,000 psi with Blue Dot-- sized groove dia. Time to peak psi is fairly quick and bullet movement might be .4" or so before said peak. Where's that bullet base at peak?? In the 06 barely to the neck end maybe entering the throat origin which likely is 312+. But what is the possible dia of said slug due to the softeness of the alloy when it's in the neck still? Heck-- maybe .315-318" before the combination of the neck wall against the chamber wall limits this obturation. See my point? what you've sized that sucker at and what it enters the rifling at are two VASTLY different dia's...due to the obturation of the bullet.. due to it's softeness.. due to the relative quick speed of the fuel.

Now-- as it's farily well know, I heat treat about everything for rifles. Why? NO obturation at the psi's and speeds I'm employing. The swaging of the bullet at it enters the throat barrel.. being oversized, promotes my gas seal. But the dia of said bullet is LESS than your sized ww alloy slug NOT treated as it enters the throat. S0-- the sized ww alloy slug should be finning more than the heat treated slug-- which was larger when loaded. Is that understandable??

Everything fins to some degree. So out to the range when the 'Sunday blasters' plaster the snow with all manner of bullets.. in the spring after melt and pick up some bullets and look at the bases. About all of them fin to some degree.

Fire a slug thru slowly as I do to examine bore size and look the bullet over closely. Does the lead displace uniformly around the bullet? No. It varies. Does this matter- Yes.... IF you have the gun to determine that kind of variable.