In the old days, with the old breed of 155’s which were shorter and blunter, the 1:13″ twist was plenty. However, with the new breed of 155’s being longer, they are certainly more comfortable in a 1:12″ or faster. By ‘more comfortable’ I mean potentially better BC’s, especially in high density air (cold and near sea level).

As for over-spinning bullets, the downsides to this are not as bad as many fear. If the bullets are poorly balanced, then you might see some added dispersion due to the imbalance, but most bullets made these days are very well balanced. Another potential downside is bullet failure, but this is more of a problem for the long heavy bullets which already require somewhat radical twist rates: 6mm 115’s for example going from a 1:7″ to 1:6″ might cross the line.

In summary, there are benefits to spinning bullets faster than previously thought (SG of 1.4), and the downsides of ‘over spinning’ bullets are not as bad as many think. The specific test results are planned for publication later this summer.

-Bryan

Folks should keep in mind though that this Miller stability calc is a rule of thumb only, so there are assumptions and it’s limited in application.
For example, it can’t account for a change in meplat diameters, plastic tips, nose shapes, or base shapes(flat/boat tail), etc.
That’s not to say it isn’t useful, rules of thumb are easier(like Greenhill). But you need to consider their limitations.