Model 25-5 Throat Sizes - AGAIN!

[keithherrington]

In the post below I referenced a quest of mine to sort our Model 25-5 throat sizes. I was plagued by oversized throats on an early pinned model 25-5 (N6798XX) of between .458" and .459". But about a year ago the S&W Performance Center replaced it with a new cylinder from their latest production run. Performance immediately came up to what you'd expect with a quality S&W N frame - routinely printing 2" groups at 25 yards and 4" groups at 50 yards. I then bought a late production unpinned 25-5 (BAN63XX) to make a comparison. S&W did some warranty work on the late model gun, replacing the bolt and the cylinder pin in the process. After everything was corrected, it too routinely produced groups on par with the earlier gun.

To finish up the analysis, I compared the throat sizes on both guns: The pinned gun with the replaced cylinder and the later gun with the original cylinder. I had my rifle smith do the measuring for me using his most precise bore micrometer. After carefully calibrating the micrometer, these are the results.

N6798XX: .4531", .4531", .4532", .4532", .4532", .4535"

BAN63XX: .4530", .4531", .4532", .4532", .4532", .4533"

All the lead bullets I've been using to test the guns are sized .453". However, after everything was said and done, the 250 grain Laser Cast RN FP over 8.5 grains of Unique with a WLP primer has consistently produced the best results. Although Laser Cast advertises their bullets as .452" in diameter, they consistently measure closer to .453".

Keith