The 30 WCF did not make its reputation on 170's. For decades after its debut, the standard offering was a full patch, or a semi-patch 160 bullet that nipped at 2,000fps.
Over time, velocities increased, and bullet weights offered grew more varied, including light for caliber small game loads with lower powder levels, and the familiar 125, 150, 170 weight split we have today.
The differences in velocity between the 150 and 170 grain bullets can be as much as 400 fps, which is significant in the venerable 30. In order to boost any 190 grain bullet to 2,000 fps, which is the nominal velocity for most 170 weight cartridges, it is necessary is to exceed maximum mean pressures. This is possible for BBA because they are NOT a Saami manufacturer. This also means that you accept certain givens if you choose to use this ammo, and that includes risking yourself and your gun.
In the days when loading 190s into the 30 WCF was popular, the prevailing idea was that ballistic coefficient was the key to controlled expansion. This was only true given equal quality of bullet construction. In similar bullets, the one with the better b.c. often penetrated better. The limits of standard cup and core construction were reached and exceeded on a regular basis in those days, by many, many factory cartridges from America to the tropics.
The true secret to better performance was discovered by custom bullet makers like Mr. Nosler. True controlled expansion was accomplished via better alloys of core and jacket, together with tapering the jacket, and exposing less lead. It was this advance that revolutionized bullet technology, and provided for superior performance without resorting to dangerous pressures and heavy for caliber projectiles.
The use of 190s in the 30 WCF is a small, short chapter written by tinkerers and long since closed. Last I heard, Mr. Fadala, who remains a stalwart fan of the 30 WCF, is fond of premium loads by Winchester Ammunition, all of which feature a 150 grain bullet.
If you want or need penetration the premium offerings from Nosler, Hawk, and Barnes will provide better performance without the risks.
As to why anyone would wish to use premium bullets? Simple, because they make the 30 more effective in marginal, or difficult shot situations, and increase the effectiveness of the cartridge as an efficient and deadly round.
