Bullet Balance Compensator
The trick to solving the bullet imbalance problem would be to allow the bul-
let to spin about its centroidal axis before leaving the barrel. The centroidal
axis passes through the CG and is parallel to the geometric axis. If this could
be done, the barrel would decrease the lateral drift velocity and decrease the
effect of bullet imbalance. I tried three approaches to making a compensator
and all three attempts failed.
The first approach was to counterbore the muzzle for a distance of three inches.
For this to work the radial clearance between the bullet and bore must be
small (less than 3mils). The reason for this small clearance is that the
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Chapter 9: Bullet Imbalance
corrective effect depends on viscous interaction between the bullet and the
barrel. I tried this starting with a 1 mil radial clearance and the groups were
enormous. I gradually increased the clearance and at about a 10 mil radial
clearance the gun shot about as well as it did before modification.
After
doing the muzzle blast shadowgraph tests and seeing the small partially burned
powder granules traveling along with the bullet, I have doubts about this
method ever working. Also, after testing I sectioned the barrel and found that
the counterbore was off center. So that may have doomed the test from the
start. If anyone wants to try this, I suggest making piloted reamers in 1 mil
increments. According to computer calculations it should work, but I may
have missed something in the physical model.
Another way to compensate for CG offset would be to allow the barrel to
move about the bullet CG before the bullet exits the muzzle. I tried two
different approaches and neither one worked. One of them appeared to be
trying to work but it drew straight lines of bullet holes as a result of thermal
distortion. I tested the barrel on the bench and found that the muzzle warped
enough with a modest change in temperature to explain the drift.
While I haven’t given up on this problem I decided to go ahead and publish
this book because it is a difficult problem that may not be solvable. Mean-
while all you can do is buy the best bullets that you can find. It also should be
pointed out that bullet manufacturers are continually trying to improve the
quality of their bullets and since this data was taken some time ago the situ-
ation may have changed by now.