Bonded vs. not bonded,
lead softness etc???
Here's a good actually example: my Dad's favorite rifle cartridge is .25-06 he for years he used the 117gr Serria SBT Gameking he shot 100+ deer with it all ran an average of 40 to 50 yds before falling.
When I told him about my switch to the flat base after hearing of their increased effect and noting it myself.
He switched to a 117gr Serria spitzer Prohunter since then he has shot 30+ deer with that combo all have either dropped or ran less than 25yds.
I have noticed the same thing with a .30-06,.270,7mm mag and a .300 Win mag. all animals have either dropped or ran less distance with various flat base bullets from different makers.
Like I said in the OP I don't know what exactly is going on here but something is.