I think you should be okay, considering the minimum is 3.0, but the COL you are using is relevant, I think, my not knowing the limits of the 1866 chambers (38 Special). I believe the data presumes crimping in the crimp groove. I tested 3.0 yesterday in a Uberti Stallion and thought it was really soft shooting compared to the 3.5 Bullseye also tested, a bit snappier. Both were 125 bullets.