Barrel Movement- Part 5
In our fifth and final part of our series on bullet
harmonics and reloading brass, we are going to look at the effect of other
components in the reloading process. This will only help to further your load’s
accuracy and help you truly find your barrel’s sweet spot.
weight or design
As mentioned in an earlier article, changing components will
affect performance. Bullets of the same weight but different brand or shape
will produce different velocities with the same powder charge. This is due
in part to differences in jacket thickness, bullet bearing surface within the
bore, gas seal on the base due to shape, hardness of core material, etc.
If you change bullet brands in your load, you will need to determine if the new
bullet's velocity is above or below the previously identified nodes. Once you
do that, all that should be required to make it shoot much better is to adjust
the powder charge so the velocity is within the range your barrel likes.
Change in Primers
Changing primers will also produce different
velocities. Once you have identified what load your gun likes, it is
simply a matter of adjusting the powder charge if you change primers. In
the final accuracy analysis, the only substantial difference between primers
may be the thickness of their shells. There is, however, a difference in
velocity they produce with a given powder charge,sometimes 50 f/s or
more. Is there a real difference when charges are adjusted to deliver the
same velocities? For all but the most die-hard reloaders, probably no.
and tracking data
Most shooters are familiar with the measurement called
"standard deviation." Standard deviation (SD) is simply a statistical
measurement of the uniformity of a sample of events. The standard deviation
data provided by most modern chronographs will help identify good loads.
While it is not always true that loads with the lowest SD produce the very
smallest group, generally a good load will have a low shot to shot velocity
Velocity deviation can sometimes be controlled by seating
depth, neck tension, flash hole deburring, etc., and these are things you can
worry about after you get a good load and have some free time to play around
with the really fine tuning. The bottom line is, however, that if you don't
have data for comparison, you cannot fine tune your loads.
Obviously, the degree of care in loading, component quality,
and shooter ability all impact group size. And, of course, not all guns
are capable of shooting one hole groups, except, apparently, those owned by
some of the gun magazine writers. (Besides, if you want a 1-hole group
just shoot once!) But, once you identify node velocities for a particular
firearm with a chronograph, much of the guesswork in working up loads can be eliminated
and a wide range of components can be made to provide satisfactory
results. If you are happy with the load you can stop here.
If you are a stickler for details and want to wring the very
best out of your loads you can go a little further with some detail work to
insure maximum uniformity of your final working load. Weigh 10 unprimed
pieces of your brass and find the average weight. Then weigh all the
cases and cull any cases that deviate by more than about
3/4 gr from the average
weight, or sort them into batches by weight. Uniform the flash hole using
a tool like Midway's controlled depth flash hole deburrer. Insure that
the primer pockets are of uniform depth (but don't ream the too deep) by using
a pocket uniforming tool like Sinclair's. And then there is selecting the
very best bullets.
In the end, how much work you put in to finding the most
accurate load for your reloading brass is fully up to you. Remember, never move
to fast and always take baby steps when adjusting a load. Just the smallest
adjustment could yield the results you’re looking for.