The 66 has a slightly smaller OD forcing cone, and only a few thousandths more metal on either side. It's Achille's heel was reportedly that forcing cone eroding from very lite, ie, 125gr and under, and higher speed, Magnum loads. With 148-158+ gr loads, expect a long life with either .38 Specials or .357 Magnums - as long as the ammo is standard commercial, ie, no 'Ruger-T/C Only!' loads.
Another great 'snubby' PD/HD load is the proven so-called 'FBI' load - the 158gr LHPSWC .38 Special +P loads, such as the Remington R38S12. I have chrono-ed them at 840 fps from a 2" 10 - and 912 fps from a 3" 65 - expect 870 fps from your 2.5" 66. My pusher orders them for me for $20/50 or less OTD. Definitely not 'plinkers' - but a lot less costly than the Gold Dots (Their $14-$18 price is for 20!).
Remember to get both bore and a chamber bronze brushes for cleaning. That longer and slightly larger diameter chamber brush is a must for cleaning, and I still use Hoppes, the .38 residue before inserting Magnums. Enjoy that 66 - the best selling S&W ever - and it's gone! Go figure...
Stainz