I've shot more silhouette with the .308 than all of the other calibers combined, and although it's not my top choice as it once was, there's no denying that it's hard to find a .308 with decent bedding&barrel that does not shoot well.
I've kept accurate records since 1981.
Bottom line is WEIGHT COUNTS. Anything that will get down range will take the "short" targets (check the N140/150 SMK load in the recent Sierra manual) but it takes a flying telephone pole to knock down rams with consistency.
This is true regardless of caliber, the long bullets are usually the ones employed by successful silhouette shooters.
In the .308, I've had best luck with 190 SMK's behind stout charges of either H380 or IMR 4064. The former is dirty and latter loads like irregular buck shot from even the good powder measures. Both will work in most .308's.
I've shot tons of rams with 168's but I considered the % loss to be unacceptable.
No matter what you shoot, if you hit enough rams, you WILL lose a few now and again. As one previous respondent said - you have to hit them to have a chance to knock them down.
Take accuracy first, but if possible use a long bullet!
Gringo