In a Gunboards.com discussion concerning a lendlease M&P revolver supplied to Britain in .38S&W, a correspondent asked,

"Does anyone know if the rifling of the pieces in this contract were pitched to accept the lower weight .38 S&W round or the heavier .38/200 projectiles?"

I didn't know the answer, but became curious, and felt that more detailed information would be available on this forum.

The rifling pitch for almost all S&W revolvers, regardless of caliber, is 1:18 3/4".

Good thing you only asked about rifling twist and not bore diameter. I personally believe that S&W used the same bore diameter for the British contract 38s as was used for their 38 Special revolvers. Why bother making new cutters when existing cutters would work? However you can find “documentation” to support both theories and few people are actually set up to measure 5 groove rifling.

how many lands and grooves have a .38 spec S&W revolver?

Five. That's what makes them hard to measure.

The only S&W revolvers I know of with a different number on lands and grooves were the .45 ACPs made before the mid-1990s. They had G.I. Joe 1911 rifling as specified in the government contract for 1917s.

S&W’s standard 18 ¾” twisted .38 specials shoot 110 through 200 grain bullets just fine so there wasn’t any need to change the twist unless the British demanded it. Besides, the Victories’ sights would have been regulated for the 178 grain FMJ load the British adapted in 1937.