From a series of tests by Dr. Mann on June 18, July 16, December 26, 1898, and April 17, 1900
Test 6 (Page 16) fine weather conditions with 185 gr swaged, lubricated lead bullet breech seated and nitro primed, Hazards FG main charge, double rest. Smallest group was 1 inch, largest 2 inches, average 1.54 inches. One of the July 16th groups is shown in Fig. 6 below. It measures 1.70 inches (widest shots measured between bullet hole centers) and clearly shows the 1-of-5 shots standing off from the group. This was a very common occurrence with many groups being spoiled by this 1-of-5* off shots, which caused unending discussion in the shooting community back then. If that flyer in the Fig. 6 test was caused by a bullet with an oblique base of .006 or greater, is unknown as the bullets from that group were not recovered. However, other shooting tests by Mann with bullet bases purposely made oblique show accuracy variance similar to that off shot.

*This 1-of-5 shots (20%) hitting out of the group keys into the ratio Mann discovered shooting into a snow bank and recovering the un-damaged bullets. In one of his tests, 122 bullets were recovered, 1 in 5 had the bases out of square (oblique) with the body by .006 inches or more. Only two of the 122 recovered bullets had bases still square with the body. All others were out of square to the bullet body by .0002 up to .014 inch. The direction and amount of the oblique bases was random bullet-to-bullet and showed no particular pattern. A bullet’s base being out of square with the body by about .006 or more will cause that shot to land outside a normal group. Before firing, all bullets had bases square with the body. See pages 54-58 of Mann’s book for more detail about bullets recovered from snow bank with oblique bases. Mann was well aware that oblique bullet bases were caused by the black powder (duplex in this case) ignition unevenly upsetting the soft lead bullet bases.
Below photo shows bullet bases square plus .006 and .014 out of square as a visual depiction of oblique bases.