A three-step load development process - Sierra 6.5 130gr MatchKingsBy Eben Fourie
- 10th Dec, 2020 Dec 10, 2020, 3:28 PM
- 5 Comments
Call me a reloading geek, but the prospect of playing with a new-to-me projectile is something I really enjoy. So when Nik recently received some Sierra .264” 130gr MatchKings from NZ Ammo, and asked if I would like to evaluate them, I leapt at the opportunity.
At the time of writing, Sierra offers four 130gr projectiles in 6.5 calibre: two projectiles are oriented to hunting - a hollow point GameKing #1828, and a tipped GameKing #7430, and two projectiles are oriented to target shooting - a Tipped MatchKing #4330 and the hollow-point boat-tail version of the MatchKing #1729.
The hollow-point MatchKing is the test subject for this article. MatchKing projectiles have a long history of solid performance in the target shooting disciplines.
My load development plan was split into three phases:
- Find the pressure limit
- Identify the node(s)
- Tune group size with seating depth
This process typically uses between 50 to 100 projectiles - not an insignificant number, but well worth the effort when you end up with a load that you can have a high degree of confidence in both in terms of safe pressures as well as consistency.
Compared to the Lapua Scenar L I normally use in my 6.5 Creedmoor, the Sierra MatchKings have a slightly more tangent ogive shape, and a noticeably longer boat-tail. The meplat also looks as if it is pointed in the factory.
When I start working with a new projectile its intended use determines the route I follow. The plan for these projectiles was to use them for gong shooting in some of the Practical and Precision style matches held around the North Island.
With this in mind, I knew the overall cartridge length had to be short enough to ensure consistent feeding from the magazine, and accuracy would be more important than maximum velocity.
“This process typically uses between 50 to 100 projectiles - not an insignificant number, but well worth the effort when you end up with a load that you can have a high degree of confidence in both in terms of safe pressures as well as consistency.”
As a rule, and provided the magazine has sufficient space, I start my load development by seating the projectile 10 thousands of an inch off the lands. Having a projectile jammed into the lands is asking for trouble - often resulting in a projectile stuck in the barrel and powder all over your trigger mechanism if you ever need to extract the live cartridge from the chamber.
With the projectiles at hand, I did some measurements to determine what the “lands” seating depth would be. This task is easily accomplished using a Hornady OAL gauge (#C1000) along with the calibre specific modified case, a 6.5 Creedmoor in this instance.
Next up is deciding the powder charge. After several years of competing in F-class, I have settled on a simplified Optimal Charge Weight (OCW) method for load development.
I try to find a stable velocity “node” or flat spot, somewhere in the increasing progression of charge weights, where small changes in powder charge result in an area of consistent muzzle velocity (MV). As charge weights increase, you generally expect to see a corresponding increase in velocity.
“Nodes” are areas where this climb stops or slows down. These are areas I try to identify, because with small variances or errors when dispensing powder, or variations in environmental factors such as temperature, the effect on muzzle velocity and group size will be less drastic if you are in the middle of a node.
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Now for the counter-intuitive bit. I shoot the first phase of load development without looking at group sizes! My focus at this stage is purely on muzzle velocity, so I shoot over a quality non-optical chronograph such as a Magnetospeed or Labradar.
It is very tempting to get fixated on group size at this stage, but MV is a better metric in my view. In order to objectively identify the best performing load, very few shooters can shoot consistently small groups all day long. The chronograph is scientifically impartial.
My favourite powder for the 6.5 Creedmoor is Hodgdon 4350 (AR2209 repackaged for the American market). A quick look at the online reloading references gave me a minimum load of 35.2gr and max of 39.2gr. Keep in mind that these published figures are on the conservative side, due to liability constraints.
Both the Hodgdon and ADI websites list these values - it is always a good idea to get starting loads from at least two sources to make sure.
One factor to consider when looking at published load data is that they tend to use basic components, so in the case of 6.5 Creedmoor, more than likely large primer brass. I am currently using Peterson small primer brass.
Due to the smaller primer pocket giving more brass in the base, these cases can handle more pressure as you will see shortly. (See table below)
1) Find the pressure limit:
To establish what a safe pressure would be in my rifle, I loaded batches of two in 0.5 grain increments. The Peterson brass really surprised me, so much so that I had to make a subsequent trip to the range after going well over the book “max”. I eventually started seeing mild pressure signs at around the 43.0gr level - slight cratering and flattening of the primer.
|Pressure Limit Data|
|Date||Charge||MV||SD||# Shots||1||2||Charge Increase||MV increase||Notes|
|21/10/20||A||39.7||2602||41.0||2||2573||2631||101.28%||96.84%||first shot cold & clean|
2) Identify the node:
Having found the limit of what I wanted to work with, I then loaded five shot batches at 41.5, 41.8, 42.1, 42.4, 42.7, and 43.0. In a medium sized case such as the 6.5 Creedmoor, increments of around 0.3 or 0.4 grains equate to powder increases of around 1%.
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While I did not see an obvious flattening of the velocity curve, the standard deviation (SD) for one load was significantly lower than the rest. In my book, SD is a much better metric for velocity spread than extreme spread (ES), as it takes into account all the shots in a string, rather than just the outer limits.
Speed results / Node line graph
Having found a load (42.7gr) that I was confident would give both consistency in velocity as well as acceptable speed, the final phase was to settle on a projectile seating depth.
For my Bergara HMR, I have three different AICS style magazines to experiment with: polymer factory, polymer P-Mag, and metal Accurate Mag.
When I established the “lands” length earlier, I loaded a couple of dummy rounds at 0.010 off the lands to see what they would look like in the magazines. In the factory polymer magazine, things were a bit too close for comfort at that length...
3) Tune group size with seating depth:
For the seating depth tests, I loaded five rounds each of 0.005, 0.010, 0.015 and 0.020. As expected, one group showed significantly better performance than the rest - the group loaded to 20 thou off the lands.
This was contrary to the commonly held view than seating close to the lands is best. This group also showed the lowest vertical spread.
Remember that each rifle is unique, even two rifles of the same model and chambering are likely to have different preferences when it comes to hand-loaded ammunition.
Just because these recipes worked in my rifle, does not mean they are safe, or likely to be successful in your rifle. The golden rules of reloading apply: don’t use other peoples recipes, and when you develop your own loads - start low and work up safely.
“The golden rules of reloading apply: don’t use other peoples recipes, and when you develop your own loads - start low and work up safely.”
If you are particularly constrained in terms of time or projectile numbers, the process can be shortened by combining the pressure and OCW phases for a standard seating depth, either 10 thousands off the lands or magazine length depending on your requirements.
The Sierra 130gr MatchKings provided acceptable accuracy, and good speed. I would be happy to use these in gong shoots or field competitions.
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