I've been lurking here for years but post very little. I prefer to learn but this is a subject I'm very much in touch with. I carry plug gauges in my range bag at all times and at gun shows when I'm looking to buy. My personal experience runs the gamut from early p&r guns up to current Performance Center guns. Most every p&r gun I've measured has been in the range of .432 - .435 and none of them were consistant good shooters. Sure there were some good groups but just when I was happy wth the load bullets would start flying all over the target. After 3 or 4 different 29's and 629's I wasn't a very happy camper and I had alot of money tied up. I settled on a 629 with .432 throats and custom cast and sized .432 240gr. bullets. Then a fellow club member bought a used 629 classic and the throats measured .429. I was really excited with this discovery and volunteered to sight the gun in for him. The groups were fantastic. We used a .430 240gr. cast bullet. I lucked into a chance to buy a 629 Classic for a good price so I sold my original 629 and bought the Classic. It shoots excellent with .430 cast bullets and .429 throats.I then had a chance to buy a 629 Stealth Hunter. The throats measure .4285 and it's a tack driver with the .430 bullets. Over the past 2 years I've measured 90% of the guns that come through the doors at the pistol range and from the Classic series onward the throats all measure .429. All the Performance Center guns I've measured are right at .4285. I'm sure there's a limit here but as far as my experience goes the tighter the throats the better the gun will shoot. I've also done this with .45 Colt, .38 Special, and .41 Magnum with the same results. Remember this is for cast lead bullets. Jacketed or copper plated is a whole different animal due to the difference of friction between the two metals. The throat size is not nearly as critical with copper. Just my .02cents worth.