One of the consistent goals for any shooter when reloading brass is to develop the most consistently accurate load possible.  On the surface, the task appears daunting as one seems to be faced with having to trying hundreds of combinations in different loading manuals to find one that works well in your particular firearm.  However, as we will see, there is an easier way.

First a little theory

Every barrel develops harmonic vibrations when a cartridge is fired, similar to a string being shaken. A gun barrel’s vibration can be described as a 3-dimensional sine wave, or corkscrew movement and is caused when the bullet is accelerated into a rapid spin by the rifling.

It is impossible to entirely eliminate barrel movement.  Even a thick barrel’s muzzle will move with every shot and any velocity variation will alter where the muzzle is located as the bullet departs. This random movement of the muzzle gives rise to increased group size.  Most experienced gun builders agree it is best to allow a barrel to flex.  The idea is if the barrel’s movement can’t be eliminated the next best thing is to load rounds in such a manner that causes these vibrations to be consistent and predictable. That’s why well-made guns will often have their actions, and only the first inch or so of the rear of the barrel, bedded tightly into the stock to hold the receiver firmly, with the remainder of the barrel free floated.  In addition, short, thick barrels have wide(r) nodes so velocity isn’t as critical to achieving a sweet spot.

Since the velocity of the bullet passing through the barrel affects the way it flexes, accurate loads should deliver as consistent a velocity from shot to shot as is possible so that the bullet exits the muzzle at the same point in the “flex.”. You can control this to a degree but it is impossible to entirely eliminate shot to shot velocity deviation.  At around a variation of 10 to 12 f/s it may become almost impossible to reduce the effect any further.

Finding the “Sweet Spot”

It has long been understood that barrels perform best within certain velocity ranges.  These velocity ranges are commonly referred to as “harmonic nodes,” with the less technical name being “sweet spots”.  The reason for this is that the tensile strength of the metal alloy increases as it moves further away from its static state.  The barrel gets stiffer when it is forced to the extremity of its movement.  At the point of maximum movement, slight velocity variations change the muzzle location less; resulting in lower shot dispersion and thus a smaller group size.  What most shooters don’t understand is the harmonic vibration is related to the mass of the bullet.  Therefore, once the harmonic node(s) for a given weight bullet is identified, a lot can be learned, if you know the velocity.

There is also a new theory of “barrel timing” being developed based upon data obtained from strain gauges.  Upon firing, the chamber swells slightly and an annular ring of expansion travels down the barrel causing the bore to expand slightly and this effect continues as the expansion reflects back and forth along the barrel diminishing with each passage, similar to the ripple in water from throwing a stone.  Initial data suggests that not only should a load perform best at one of the velocity nodes but that the bullet should not exit the muzzle at the same time that the expansion ring reaches the muzzle as the slight increase in bore size adversely affects accuracy.

Importance of a Chronograph before getting started.

In the days of yore (BC — before chronographs), it was necessary to blindly hunt for loads that worked. Once a good load was found, changing any component could render the whole process useless (since changing components varies pressure and velocity) and one pretty much had to start from scratch if anything changed.  A chronograph provides direct insight into what your loads are doing, and what you need to do to make them work better. You will be able to immediately determine if a changed component produces velocity outside of the range the barrel likes.  In most cases simply adjusting the powder charge will correct the problem.

If you are looking at reloading your own brass for the purpose of accuracy and consistent loads, having a good chronograph is essential to the process. It is important that you find one that is extremely accurate and stable, as well as one that uses infrared sensors that will detect the bullet under any circumstances, such as total darkness, when other chronographs might fail to pick it up. Which chronograph to go with should be a decision made from much research and reading of reviews and choose the one best suited for your budget and needs.

Load Development

Step One

Let’s start from scratch and assume nothing is known about reloading brass for a particular firearm.  The only information we have is from load manuals.  Also, time is valuable, since we probably don’t have a range in our back yard.  Even if we are lucky enough to have a place to shoot outside the back door, saving time by doing things efficiently lets us enjoy other things in life. We will also assume that your rifle’s bore is clean and free from copper fouling, that your barrel’s bedding is correct, and that all screws are tight on your rifle. Another thing to keep in mind is that it often takes several “fouling” shots from a clean barrel for velocities to stabilize so you should fire a couple of fouling shots before starting load development.

Most reloading manuals list their loads starting with the fastest powders and work down to the slower powders.  The powders have been selected as suitable based in part on the loading density so any of the powders should work well.  If you are starting out by having to purchase powder, select one of the powders in the middle or slow end of the loading data list suitable for the bullet you will be using. This will give you “wiggle room” to move up or down, depending on the data you begin collecting in your loads.

At your reloading bench, begin by preparing the reloading brass for reloading.  Sort your brass by brand or military manufacturer/date head stamp. Clean, resize, trim (nominally to .01″ less than the maximum allowable case length as specified in your load manual–the actual length is not as important as is the lengths being uniform), and prime about 100 pieces of the same brand of brass with your favorite primer.  (The brand of components you use are not important at this point as long as all the cases are the same brand or military manufacturer/date head stamp and you use the same primers and bullets for all the cases.)

Determining powder charge

Now that we have the reloading brass cleaned, sorted, trimmed, and primed, let’s move on to determining how much powder to start off with. Check your loading manual and determine the maximum charge suggested for your powder.  Then determine how much adjustment on the powder measure will throw about 1 percent or slightly less of the weight of maximum charge of powder.

As an example, if the maximum load was 45.3 grains, you would determine the amount of adjustment of the measure that would give you about a 4/10 to 5/10 grain increment–often about 1/4 to 1/2 turn of the adjustment. Then, set your powder measure to throw a charge in the lower third of the charge weight range as recommended by your loading manual.  Also note the maximum velocity indicated in your load manual so you have some idea of when you are approaching a maximum load.

Bullet Seating

Use your preferred method to set your seating die so that bullets will be seated 10 to 20 thousandths off the lands or to the workable maximum overall length if they will be used in a magazine fed firearm.  It should be noted here that it may be a good idea to check your seating plug to ensure that it bears only on the ogive of the bullet and not the tip.  Because bullet tips vary slightly in shape, seating a bullet by means of its tip leads to varying seating depths.  It may be necessary to alter the seating plug by drilling it out slightly, so it bears only on the ogive.  Some manufacturers will custom cut seating plugs for you.

Setting a seating die for the “overall length” should be done using one of the gauges that measure from the ogive and not the tip of the bullet.  Sinclair and others make inexpensive gauges for this or you can fashion your own.

Time to start Shooting-Range Day

Head for the range with bag of primed cases, bullets, powder, powder measure, a single stage press, a seating die, and a “permanent” type marking pen.  All you will be doing is throwing powder charges and seating bullets, so how you mount the press and measure so it is useable at the range is up to you.  Some shooters just screw their stuff to a heavy wood plank. Of course, you will also be taking your chronograph, rifle rest and “sand bags,” your notebook and pencil, and hearing and eye protection.

Load 5 starting rounds and slowly and carefully fire them at an aiming point through the chronograph (This is assuming you have good bench shooting technique).  Record group size, the velocity and the standard deviation for the string.  Increase the charge one “increment” by turning your adjusting screw on your powder measure as described above and shoot 5 more at a separate aiming point. Continue this process until you start seeing signs of high pressure or reach maximum velocity.  If you get a really good group, load one sample round with that load and label it with the marking pen before adjusting the measure so you can weigh it at home later (or if you can weigh charges at the range do so and record the charge weight).

Judging Velocities 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.

Barrel Thickness

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.

Changing Bullet 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.

Standard deviation 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 deviation.

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.

Wrapping Up

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.