Posted by 65guys | on January 11, 2015 | 4 Comments
Now that we have the basics down, we regularly revisit each aspect of our reloading practices and ask how we can improve them. In this article we will discuss compressed loads, their impact on bullet seating depth and concentricy, and what we are doing to minimize those variances. We will also discuss our philosophy around continuous improvement and how it drives us. As always, we look forward to the feedback we will receive because there are always opportunities to improve.
Chances are you have heard of Kaizen which is the practice of continuous improvement. It’s the secret sauce that allowed Japanese manufacturers to capture market share with high quality goods. We like to joke around that we have OCD, but we believe our shooting improves when we regularly reexamine every aspect with Kaizen in mind. Minimizing seating depth and concentricity variations may not be the difference between winning and losing a match, but those improvements combined with other improvements will have a cumulative positive impact. But there is also a balancing act to be had – you don’t want to dissipate valuable time embracing practices that give little or no benefit. Shooting is a mental game and knowing that you are controlling variables to the best of your ability, and in a way that creates a net benefit given the time involved, will give you additional confidence.
Many of the popular loads for long range precision shooting involve powder fills at or close to 100% with long high BC bullets that push down into the powder column. These compressed loads result in the familiar crunching sound one hears when seating a bullet. As we demonstrate in the video, unless the powder is completely settled it will push back against the bullet a little differently each time. These differences will result in seating depth variations but will also affect conentricity due to bullet yaw. The goal is to settle the powder as consistently as possible across all cartridges and if possible avoid powder compression altogether. Even if a load remains compressed, variations can be minimized with consistently settled powder.
We employed two different tools to measure these variables, and have the following observations:
We measure concentricity with the Sinclair tool. There are a number of different tools out there and they can provide different measurements depending on how they hold the cartridge and where on the cartridge the measurement is being taken. We see all sorts of concentricity measurements shared on the internet, but they are not very useful without knowing how the measurement was taken. As for us, we have taken some baseline measurements and we adjust our reloading practices to minimize those variations.
We measure seating depth from base to ogive utilizing the Hornady Lock-N-Load tool and a set of digital calipers. These are very popular (they have become the de facto tool it seems) and take inserts from other manufacturers such as Sinclair. As we illustrate in our video, it’s important that the case is square to the caliper jaws in order to get consistent measurements. Since this tool is so popular, we find it easier to share measurements with other reloaders.
In the making of our video on this topic, we conducted a quick test to illustrate the effect of compressed loads on seating depth and concentricity. We loaded five cartridges with no powder (our control), five with unsettled powder, and five with settled powder using vibration. While not a statistically valid sample, it does illustrate what we’ve been seeing: Cartridge overall length increases and concentricity decreases the less powder is settled. If you ever adjust your seating depth using a dummy round with no powder, this explains why your charged loads end up being longer. You’ll also notice that bullets will seat deeper with each pull of the lever as the powder column settles. This can drive you crazy until you understand what’s going on.
Neck tension also plays a role and we employ about .0015″ to .002″ using Lapua brass. In other words, our bullets are seated firmly and are not being pushed back out by the powder. Years ago Ed charged some .308 cartridges with Varget well into the neck to see if a bullet with .0015″ to .002″ tension would get pushed out over time. He marked the COAL on the brass with a Sharpie and measured them from time to time and did not observe any growth. To make a long story short, he found the cartridges about seven years later in the back of his reloading drawer (he’s not as organized as Steve) and they had not grown at all.
Why do we bring this up? We don’t believe the variances we are observing are due to a lack of neck tension on the bullet. This is an educated guess, but we believe the area where the seating stem meets the bullet may flex and allow the bullet to slide further up. There may also be some bullet deformation involved. Perhaps a custom made seating stem would minimize these variances? We would welcome any empirical data our audience members might have on this topic.
We are currently employing vibratory methods to settle the powder. Ed achieves good results by touching each cartridge to the side of his vibratory cleaner prior to seating the bullet. Steve achieves a somewhat better result utilizing an ultrasonic toothbrush. We’ve even seen people using electric razors to settle powder.
Many reloaders employ drop tubes, but it is reported that lengths in excess of two feet are required to achieve the desired level of settling as illustrated below:
During the making of our video, it wasn’t clear how we could practically utilize a two foot (or longer) drop tube but members of our audience have pointed us in the right direction.
Longer drop tubes are typically mounted in a stand as illustrated to the left.
A stand mounted drop tube can accommodate individual cartridges or a full tray of cartridges. We found a couple of videos showing how to make one at home (we’ll provide the links below).
We believe that a stand mounted drop tube could deliver the desired level of powder settling in minimal time. We’re going to construct one and see how it works. We’ll be sure to test other methods presented by our audience and report back.
Here are two other useful videos on constructing a drop tube: