I noticed RCBS lists their silhouette molds separately from their rifle bullet molds, and the silhouette molds have only 1 lube groove. What is the advantage to this style of bullet? I'm considering the 165 gr for .308 Win at 1800 to 2000 fps, for the supposed advantage of keeping the gas check in the neck of the case. Who can help me figure this out?

I'm not 100% sure about this, but I believe those molds are intended for handgun silhouette shooting. The single lube groove is indicative of the lower velocities attained when using heavier (for caliber) bullets in handguns with smaller cases and shorter (than rifle) barrels.

I use a 7mm RCBS Shilloutte mould in my 7x57Mauser. This design has a long bore riding nose to align the bullet prior to firing. I am achieving 1900fps with 28.5gn 3031 with excellent accuracy and power.

Similarly the Lyman 311284 210gr for my 30.06 has the long nose and at about 1600fps has all the accuracy and power I need.

The real secret of shooting cast is not to try to get the highest velocity but to get the best accuracy at moderate vel.
I can shoot both these loads to about 60-70 shots with no loss of accuracy

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