Let’s clear up all the confusion and misinformation about consistency, accuracy and repeatablilty.
ookie shotshell reloaders often have the same questions. At least once a week I hear from a reloading newbie who is appalled to find some (or all) of the powder bushings supplied with his new reloading machine don’t dispense the precise weight of gunpowder the chart says they should. The newbie is understandably full of questions at this point, wondering if he’s doing something wrong or if his machine is defective.
That is the proper attitude! A good dose of apprehension and question-asking is healthy when engaging in any activity in which you’re still a beginner – especially one like shotshell reloading. A beginner who reads the instructions and asks coherent questions is well on the way to becoming an expert.
Charge Bars & Powder Bushings
For those who have chosen one of the popular MEC (Mayville Engineering Company) reloading machines, it’s usually just a matter of time before they hear about a MEC-compatible device called the “Universal Charge Bar™” (henceforth, referred to as the “UCB”). The UCB is made by a separate company (distinct from MEC) called Multi-Scale Charge, Ltd. and is made only for MEC loaders. The UCB has been on the market for many years and thousands have been sold and enjoyed by their owners over the decades. Ditto for the MEC reloader.
Common to any reloading machine is the need to drop a controlled amount of powder and shot into each shell. MEC’s design concept for doing so is a good one (many reloaders use a similar system of bushings). On MEC loaders, a single square-section aluminum bar (the “charge bar”) travels back and forth in the loader, dropping powder and shot at the appropriate points in each hull’s trip through the reloading cycle. Each MEC charge bar features a fixed-sized cavity at one end that delivers a specific shot weight.
As can be seen in Figure 1 (above), this cavity is nothing more than a hole of a specific diameter that MEC drills completely through the bar. All MEC charge bars are essentially the same except for the size of the hole. In other words, if you want to drop 7/8-ounce of shot, you must use a 7/8-ounce charge bar. If your reloading recipe calls for 1 ounce of shot, you buy a 1-ounce charge bar, and so on.
A second cavity at the other end of every MEC charge bar is where you insert one of the powder bushings. To change the amount of powder dropped, you remove the powder bushing and replace it with another with a larger or smaller hole, as appropriate. MEC manufactures about 50 different powder-bushing sizes (the size of the bushing is identified by a number stamped on the outer surface).
As an alternative to MEC’s fixed-sized bushings and charge bars, the UCB features user-adjustable cavities that control how much powder and shot are dropped into each shell (see Figure 2 below). The major benefits of the UCB are obvious. Instead of changing the bushing to alter the amount of powder dispensed (or change the entire bar for a different amount of shot), you simply dial the UCB to a different value, making one or both of its adjustable cavities larger or smaller as required. The biggest advantage to the UCB’s adjustable powder cavity is the ability to easily obtain an amount of powder that is “in between” bushing sizes, if that’s what your recipe specifies. Similarly, the adjustable shot cavity allows you to compensate for shot size and density differences to get the exact drop weight you need. For example, a MEC charge bar that may drop a perfect 1 ounce of hard (high-antimony) No. 7½ lead shot will often drop a slightly different weight of soft (chilled) No. 9 lead shot. You can adjust the UCB to get exactly 1 ounce of each.
Adjustability naturally sounds intriguing to a neophyte, who asks, “Should I get a UCB? Will it eliminate all the problems with fixed powder bushings?” If our hungry-for-knowledge student posts these questions on an internet forum, stand back! Replies usually run the gamut from “The UCB isn’t worth the hassle of adjusting it” to “Everyone should get a UCB, since fixed bushings are so limiting.” Especially vague are those comments that wrongly use the terms “accuracy,” “consistency” and “repeatability.” As with many choices in this world, one isn’t necessarily better than another – just different. Let’s try to set the record straight here once and for all.
Every reloading-machine manufacturer, including MEC, publishes bushing charts. For each gunpowder type commonly used for shotshell reloading (listed by exact “make and model,” such as Winchester Super Target or Alliant Red Dot), the chart lists the amount of powder (in the standard reloading weight unit of “grains”) that will be dropped by each of the various sizes of fixed powder bushings.
For example, MEC’s chart says their #28 bushing drops 16.4 grains of Alliant Red Dot. This is where our newbie expresses questions and concerns. Instead of 16.4 grains of Alliant Red Dot, he may find his #28 bushing drops a little more or less. Or he may observe the amount of powder shows a small variation from shell to shell. He may have even detected the same #28 bushing drops a slightly different powder weight in June than it did last December.
Since our rookie knows what the bushing is dropping, it’s obvious he/she is using a reloader’s scale. Well done! For all you other reloading trainees, if you don’t own a proper scale, whoever sold you that reloader should be horse-whipped for allowing you out the door without one. In fact, don’t even read the remainder of this article: Go out now and get a scale! I’ll wait right here.
What’s going on with our rookie’s #28 bushing? Some folks erroneously say it’s inconsistent because it doesn’t drop the exact same weight of powder each and every time. But a fixed-size hole in a solid chunk of aluminum clearly cannot be inconsistent. Something else is happening.
It is a well-known experience among reloaders that the machines we use for shotshell reloading do not always drop the exact same weight of powder or shot every time. The variations will be small but present nonetheless. This is caused by a number of factors, none of which point to any defect in the machine, bushing or powder. It is caused simply by a common trait shared among all reloading machines – the powder and shot cavities are filled prior to each drop via gravity feed from the reservoirs atop the machine. For powder, the following issues can affect the consistency of how much powder enters the bushing each time it is filled.
- Physical properties of the powder you’re using, of which density and size/shape of the individual granules have the greatest effect on drop uniformity. Some powders are a little less consistent than others in how they flow and pack themselves into the bushing.
- The amount of powder in the machine’s reservoir. The total weight of the powder above the bushing is what pushes each charge, via gravity feed, into the bushing. A full reservoir provides more down-force than one that is near empty, which can cause some powders to exhibit a small variance in drop weight as the reservoir contents are consumed. Most machines incorporate a powder baffle in the reservoir (or one is available as an add-on) that keeps a consistent weight of powder above the bushing no matter the total amount in the reservoir, essentially eliminating this source of non-uniform powder drops.
- Erratic operation. Do you consistently operate the machine, raising and lowering the handle with the same force and tempo each time? Or do you cycle it gently one time and slam-bang it the next? Inconsistent operation can cause powder drops to vary slightly.
- Powder variance. Even though the gunpowders sold to us for reloading are known as “canister grade” (meaning all physical properties are tightly controlled for consistency), two containers purchased from different production lots sometimes exhibit very small differences in density which can be detected by a reloader’s scale. A powder’s metering properties can also be affected by air humidity and temperature, which explains why a bushing might give a slightly different drop in June compared to December.
The important point here is the small variation in powder drops everyone experiences is inherent to the gravity-feed machines we use. Assuming your machine is mechanically healthy, firmly mounted and functioning as the manufacturer specifies, it will be as consistent as possible, which is to say, pretty darn good. Any observed powder-drop variations from shell to shell will be very small (often near zero) and certainly within safe and accepted norms.
Here would be a good place to note if your measurements show powder (or shot) drops with large variations, you have a serious problem – a defect that is certainly not an unavoidable characteristic of gravity-feed machines. Your machine may not be bolted down properly, the charge bar may not be traveling its full cycle distance back and forth, something is not screwed down tight causing leakage, there is a blockage in the drop tube, or the machine is damaged. No machine in poor working condition can deliver proper results. Find out what’s wrong and fix it!
Is a UCB more consistent? Why would it be? All the factors that cause the small variations with bushings are due to powder properties, environmental conditions or operator behavior, not the bushing itself. The same issues equally affect the UCB’s consistency. Once you dial the UCB to the desired setting and lock it there, you essentially have a fixed bushing. The powder and shot in the machine’s reservoirs cannot tell whether the holes underneath them are fixed bushings or a UCB. A hole is a hole. As far as consistency is concerned, it’s a dead heat.
The only thing that could cause the UCB to produce inferior consistency would be if its adjustable cavity moved while you were reloading. The locking set screws on the UCB prevent such unwanted movement. Install, adjust and lock the UCB according to the manufacturer’s instructions, and drop weights should be just as consistent as a fixed bushing. Note the same caveats apply here, also. The machine must be in proper working order to deliver safe results with bushings or the UCB.
How do you define accuracy for a bushing? Some claim a bushing is “inaccurate” if it doesn’t drop the exact weight the bushing chart says it should. Not true. As we’ve already seen, humidity can have a slight effect on how much powder a bushing will drop from one day to the next, as can the vibrations the operator gives the machine.
Furthermore, the same bushing will often drop slightly different amounts depending on whether it is installed in a single-stage or progressive machine, usually heavier in a single-stage. Why? A progressive machine drops a powder charge with every stroke of the handle. A single-stage press drops a charge only once per multiple handle pulls, meaning the powder spends more time in the bushing before it is finally dropped. While it is waiting to be dropped, machine vibration may cause some “settling of contents,” as the saying goes, packing a little more powder into the bushing.
So technically, it’s the chart that’s inaccurate, and even that is nowhere near a fair statement. It is more precise to say the chart cannot possibly be exactly right under all conditions. Some days a bushing will drop exactly what the chart says; other days it may drop slightly more or less. The real reason the chart exists is to narrow to a few the number of bushings that stand the best chance of dropping the amount of powder your recipe specifies. And for this purpose, the chart does a perfect job. Without the chart, you might end up testing every bushing in the box until you stumble upon the correct one. Notice I said “test” each bushing. The existence of the chart in no way releases you from the responsibility of using a reliable scale to determine which bushing drops the amount of powder or shot you need.
So, a bushing cannot really be “accurate” or “inaccurate,” especially if you define those terms as “agreeing with the chart.” A bushing will drop whatever amount of powder or shot fits into it under the conditions and influences that exist right there and then, no matter what the chart says. You must verify via a scale what a bushing or charge bar is producing for you in your machine, prior to each reloading session. That’s a Fundamental Law of Reloading. Adhere to it always.
There is, of course, a chart supplied with the UCB, too. It is analogous to the bushing chart, except, rather than bushing numbers, it lists the adjustment settings that yield the powder and shot drop weights you need. And, just like the bushing chart, the UCB chart can really only get you close. It gives you a good starting point for your first test weighings, thereby avoiding a time-consuming search for the correct setting.
With the UCB set to the chart’s recommended setting, if your test on the scale is a little light, open the adjustable cavity a small amount and test again. If it’s a little heavy, close the cavity a little bit and re-test. The setting that yields the drop weight you need is sometimes exactly what the chart says, but sometimes itís a little different. If itís a lot different, be suspicious. Check all the usual suspects: leakage, misreading the scale, blockage in the drop tube, using the wrong powder, etc. By the way, the same advice applies for fixed bushings – if your test weighings disagree with the chart by a significant amount, something is wrong somewhere. No chart is ever that far off!
Therefore, it’s again a tie between fixed bushings and the UCB. Neither can be truly termed “accurate” or “inaccurate” in relation to the chart. And, just like fixed bushings, there is no feature of the UCB or its chart that excuses you from using a scale to test your loads. The chart can never tell you exactly what your bushings or UCB drop – only you and your scale know that.
“Repeatability” could be defined as returning to an exact hole size previously used or returning exactly to a previously used drop weight. Confusing those two concepts – or worse, thinking they are the same – is responsible for most of the misguided complaints about the UCB. For the former, the bushings and the UCB again tie. For the latter, the UCB wins hands–down.
It’s easy to repeat (return to) the same hole size with bushings. If you remove a #28 powder bushing from your machine and put in a different size, all you need to do to get the original hole size again is swap back to the #28 bushing. Simple.
You can return to the exact same hole size with the UCB, too. It’s not quite as fast, but it’s still easy to do by following the manufacturer’s instructions. You need to learn how to read the UCB’s settings via its two–part index markings, however (admittedly, older eyes may need a little magnification assistance). But if you understand how to read your balance–beam reloader scale, you can understand the UCB.
You must also understand the reason for the “always approach a new setting from below” rule. This is due to the small amount of “lost motion” inherent in nearly every mechanism in the world that uses screw threads. Grab an ordinary nut and bolt from your toolbox, look up “lost motion” on the internet, and you’ll quickly be able to teach yourself what “taking up lost motion” means and why it’s important. So, as far as repeatability of hole size is concerned, bushings and the UCB tie again. The UCB takes a little more effort, but its hole size is no less repeatable.
As we’ve already covered, the same hole size (bushing or UCB) may or may not drop the exact same weight you got the last time you were at that setting. So those of you who think dialing the UCB back to a previous setting is the same as re–obtaining the same drop weight are incorrect. Complaints about the UCB’s repeatability based on this false notion are, therefore, undeserved. Furthermore, the same folks probably think adjusting the UCB back to a previous setting means you don’t need to re–check the drop weight with a scale. Anyone who tells you that is just plain wrong.
So actually, the UCB beats bushings on repeatability. To return to a previously used drop weight, just tweak the UCB slightly to whatever setting scales out according to your scale, even if that isn’t the exact same hole size you used before.
Pros & Cons
To state the patently obvious, the advantage of the UCB is it’s adjustable. It, therefore, has excellent “granularity” or “sensitivity” simply because it is adjustable and due to its method of adjustment (turning a screw). Such an adjustment method means the hole size can essentially be set to an infinite number of different positions, each varying by just the slightest movement of the adjustment screw. The only way fixed bushings could come close to this granularity would be if the manufacturer marketed literally hundreds of different bushing sizes, which would be rather impractical.
Should you use fixed bushings or a UCB? If you tend to stick with a small number of reloading recipes, bushings are perfect. If you like to try every recipe in the book, the UCB will serve you well, saving money you might otherwise spend on a box full of charge bars and bushings for your loader.
Since shot with lots of antimony is less–dense than pure lead, fixed shot bars often drop a load that is a little light with such “hard” shot. Some shooters simply can’t sleep at night knowing the guy next to them might have five more pellets of No. 8s in his shell than they do. The UCB will allow you to tweak the shot setting so you can get the full shot load, by weight, your recipe specifies.
Whichever your choice, it should not be based on any misconception about accuracy, consistency or repeatability. Now, let’s go reloading!