Barrel Movement- Part 4
In part three of this series on Bullet movement and how it
affects reloading brass, we made it to the range and began firing a few test
loads. Now we are going to take the data and begin making modifications to our
load for optimum accuracy.
and finding the “Sweet Spot”
Earlier in this series, we spoke of the “sweet spot” in your
barrel’s movement and how that sweet spot gives the bullet the best chance at
ultimate accuracy. This is where we begin to find that sweet spot.
As velocities increase you should see obvious changes
in-group size. It should be readily apparent when you reach a velocity
node the barrel likes. However, don't stop at the first point where you get a
tight group as most rifles have two or more nodes. As you pass through
each node, groups will open up again until you approach the next node.
Stop only when you are at maximum velocity or pressure. Once there, you
should have identified rough velocity nodes for the bullet's weight. It's
now time to get serious. If you can weigh powder charges at the range you
can proceed there, otherwise it's time to head back to your loading room.
Step 2--Fine Tuning
At this point, most of the drudge work has been completed
and it is time to begin fine tuning your reloading brass loads. You should now
have a good idea of which velocities allow you to hit the “sweet spot;” it will
be the loads that caused the tightest groups on range day. Pull the bullets
from the sample loads that produced the best groups and carefully weigh the
charges. Load at least 5 more rounds of each "node load" using
your best reloading technique and another 5 each just over and under that
charge (say 1/2 of
the initial "increment). Return to the range with your loaded rounds
to validate what you have learned and if possible also determine the velocity
range/width of each node.
While loads at the different node velocities will all
perform well, if you are developing a target load which you will be shooting the
most of, you may want to develop your load around the lower velocity nodes as a
means of keeping barrel erosion to a minimum. For a hunting load where
you want to get maximum ranging and terminal performance concentrate on the
higher velocity nodes.
Generally, the thicker the barrel the wider the node.
This is important when working up loads that will be effective during different
times of the year. For example, loads that work in 110 degree heat often
perform poorly in the cooler winter months. Conversely loads identified
in winter months often produce velocities that are too high to work during the
summer. Most of this is due to changing interior ballistics due to
temperature changes and not other differences in atmospheric conditions.
By identifying the width of your nodes you should be able to find a load the
works all year long. Simply use the high end of the node you are loading
to if shooting in significantly colder conditions then when the load was
developed, and load to the low end if shooting in significantly warmer conditions
then when the load was developed.
If you’ve come this far in the process, chances are you have
an idea on the best load for your firearm. In part five, the last part of this
series, we are going to look at some more technigues and data that will further
increase your load’s ability to work in your gun’s optimum point.