I acquired a very nice 27-2, 8 3/8" barrel and benchresting 38 wadcutters it doesn't group them as well as it should at 25yds. I'm quite disappointed.
Shooting jacketed bullets at near max loadings it shoots one hole groups.
I'm thinking the barrel twist rate might have something to do with this.
Does anyone know?

My old 4th edition of the Hornady reloading manual used an 8 3/8" 27 for load development. They have the twist rate listed as 1 in 18 3/4 inches in the book.

The twist rate for nearly all center-fire S&W revolvers is 18 3/4", including all target types such as the K-38. The only exception is the .44 Magnum guns. Twist rate is not the problem is your gun does not shoot wad-cutters well.

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Gunsmithing since 1961

If it's any consolation, my 8 3/8" 27-2 didn't shoot them well either.

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-jwk-
US Army '72-'95

I have "cured" some revolvers that were inaccurate with HBWC lead bullets by cleaning ALL the copper fouling out of the barrel and then shooting nothing but lead for the evaluation. After some fouling shots, the miscreant revolvers settled down and shot normal HBWC loads well. Some shot my loads well, but did not like the owner's loads; HBWC don't like higher speed and may even separate into two parts.

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Science plus Art

I have a Douglas barrel blank and 1x14twist 38 special is stamped on the breech end of the barrel. Colt twist rates were pretty close to 1x14 twist. Maybe one reason Colt barrels were used on the Smython conversions on S&W revolvers. Frank

From what all I can read other places a 14 twist stabilizes 148gr HBWC and 180gr cast bullets a lot better than factory 18.75 twist.
Also all aftermarket 38 and 357 barrels that I know anything about are 14 twist.

I just talked to Clark Custom Guns this morning and they said they install only 1/12 twist barrels on all the 38 and 357 barrels they install. They said the factory S&W barrel twist of 1/18.75 is too slow to stabilize wadcutters well.