More from Compton
p. 123 Effect of choke (.000 - .050) on lateral pattern spread at 40 yds.
p. 128 It was found that for the same (choke) constriction the 1" parallel section produced a slightly tighter distribution of pellets at 40 yards than the linear taper profile for every batch of ammunition tested. However, the standard errors associated with the distribution show that statistically there is no significant difference between the two profiles, expect for the one steel load tested where an improvement is seen when using the 1" parallel section profile.
Now this is strange!
p. 129 The other variable which can be altered in the test barrel to change the internal ballistics is the chamber length. In Table 3.10 the standard deviation and pellet counts at 40 yards are given for a 36g load of #4 lead shot loaded into a 2 3/4 cartridge cases which were fired through a selection of chambers lengths. The averaged results show a definite alteration to the lateral dispersion of the shot cloud large when using the wrong chamber length. The tighter pattern generated by 2 1/2 chamber length may be caused by the restrictive crimp opening acting like an internal choke.
Altering the chamber length changed the lateral dispersion of pellets and increasing the constriction of linear tapered profile chokes over 0.030" has little effect on the lateral pellet distribution.
These findings reinforce the attitude that many aspects of shotgun ballistics, especially patterns, have no satisfactory theory to predict or explain the effects of the internal ballistics of a gun on the downrange behaviour of a shot cloud.Well that 'splains everything
