Depends on velocity

by Glen, Saturday, April 22, 2017, 12:56 (2710 days ago) @ Hoot

Below about Mach 0.8 (~850 fps), one observes a conformal slipstream around a projectile. In other words, the air flowing past the bullet conforms to the bullet's shape and is flowing more or less parallel to the surface. That conformal slipstream starts to get distorted above about Mach 0.8, with a larger turbulent boundary layer forming along with a vestigial bow wave. By Mach 1.0 (~1080 fps) one observes a well defined separate bow wave in front of the bullet, and emanating backwards at an angle.

In part, a bullet's stability is influenced by how well the bullet's ogive interacts with this bow wave and turbulent boundary layer.

One of the issues facing a true cylindrical wadcutter is the complete lack of an ogive, so any yaw (precession) is destabilizing. For a round-nose or spitzer bullet shape, the ogive fits inside this, and the bow wave serves as damping agent to dampen the yaw. For a true cylindrical wadcutter, there is only an edge, and a large flat face, so not only is there nothing to dampen the yaw, the large flat face can actually amplify the yaw, leading to instability (and ultimately tumbling).

Nowadays, most people associate the term wadcutter with what used to be called "button-nosed wadcutter". The purpose of the "button-nose" is to provide kind of a "false ogive" and generate a little bit of stability, and extend the useful range.

I did some testing with an ogival wadcutter in .44 Magnum a number of years ago. It weighed 365 grains and I was shooting them at about 1125 fps from my 7 1/2" Ruger SBH, as I recall (I was looking for a short range hog thumper load). Groups were good at 25 yards, and still pretty good at 50 yards. Shooting at impromptu targets on the hillside at about 80-90 yards was an eye opener for me -- about half of my shots hit close to the point of aim (within a few inches), and about half of my shots missed by 10-20 FEET. Clearly, some of those bullets were starting to tumble somewhere around 60-70 yards or so.