Creighton Audette came up with a method for developing precision rifle handloads that has been referred to by many names:
- Incremental Load Development Method (ILDM)
- The Ladder Test
- 20 Round String Method
Unfortunately many of Audette’s original articles aren’t very accessible, so I wanted to provide a few resources that help flesh out the method to load development he proposed. I recently tried it out, and although at first I admit I was a little skeptical … after seeing the real world results and some critical thinking about what we are really trying to uncover when doing load development, his method seems to make a lot of sense. At the very least it provides a great starting point for testing a particular bullet, powder, primer, case combination, and will likely save you some time, frustration, and barrel wear.
- Brief Overview of Audette’s Incremental Load Development Method (Excerpt from Precision Shooting Reloading Guide, Published 1998)
- Complete Deep-Dive Into Method & The Science Behind Why It Works by Randolph Constantine (Published in Precision Shooting Annual, 1997)
My Ladder Test Results
I was trying to develop an accurate load for my Rock River LAR-15 Varmint firing Berger’s 22 Caliber 77gr Match OTM Tactical bullet (relatively high BC for 22 caliber, G1 = 0.376, G7 = 0.192). I typically favor with Hodgdon’s Extreme Series powders, because of their proven consistency and insensitivity to extreme temperatures. So in that line-up, both Varget and H4895 were good candidates. Looking through reloading manuals and online sources, I found a wide variety of min/max loads for similar bullets like the 77gr Sierra MatchKing and Hornady’s 75gr A-Max, and eventually came up with these as my starting/max loads:
Min/Max Loads for Naked Bullets
|Powder||Starting Load (gr)||Max Load (gr)|
However, that was for “naked” bullets, and I was also planning to coat the bullets using David Tubb’s Precision Blended Boron Nitride (HBN) to further increase BC, reduce barrel wear and fouling, improve the first/cold shot grouping with subsequent shots, and hopefully improve accuracy as well. One of the side-effects of applying a bullet coating like HBN or moly is that because it reduces bullet friction in the barrel, it will reduce chamber pressure and muzzle velocity. To offset that effect, you need to increase your powder charge to get back up to the muzzle velocity of naked bullets. One cool side effect of this exchange is that chamber pressure will still be lower than it was with naked bullets, even when you increase the powder charge enough to attain the old muzzle velocity. For more on this topic, see http://www.6mmbr.com/bulletcoating.html or http://www.6mmbr.com/normamoly.html.
In Norma’s testing, they typically saw a decrease in pressure by 3-5% for coating bullets over naked bullets (depending on cartridge, bullet, & powder). To offset that affect I decided to increase my max load around 104% of the naked bullet max I found in reloading manuals and keep a very close eye out for signs of excessive pressure.
Adjusted Min/Max Loads for Coated Bullets
|Powder||Starting Load (gr)||Typical “Naked” Max Load (gr)||~104% of Max Load (gr)|
Targeting Audette’s suggested 2 grain increments, the spreads between starting and max loads allowed me to load 15 rounds of each powder. This didn’t get me the “20 Round String” Audette suggested, but with such a small cartridge like the 223 Remington that would be difficult to do since there is such a narrow window between the starting and max loads recommended in reloading manuals. I also loaded an additional 5 rounds of each with the starting load to use as foulers, since I planned to start each string with a clean barrel.
I used a Competition Electronics ProChrono Digital Chronograph, which is accurate to +/- 1% of the measured velocity. Here are the recorded velocities of each load for both Varget & H4895 (10’ from the muzzle):
The target below (which was set at 200 yards) shows the bullet impacts for the Varget test rounds. Although I tried to find a windless morning, those are extremely rare in West Texas … so I did have horizontal drift because of the wind. One key to the Audette method is to use the exact same point of aim each time without making any adjustments. You can see that the points of impact correlate to the recorded muzzle velocities, and the tighter groups relate to the flatter portions of the velocity chart. (Note: Where they don’t match, you could likely blame my shooting.)
The H4895 target was erratic, just like you would likely expect from its velocity chart. It was even difficult to keep track of which shot was which because one shot would be up, then the next down … just like the velocity chart showed. This led me to eliminate it as a powder choice for that bullet. It simply indicated that with that bullet, primer, case combination … the powder didn’t compliment the natural harmonics of the barrel. It doesn’t necessarily mean Varget is more consistent in all cases, it just was for that combinations of components in that particular rifle.
As a result of this test, I’ve discovered two ranges of Varget powder weight that show very little sensitivity to minor changes in charge weight and/or pressure. At this point I plan to do more detailed testing within those specific ranges by loading 7 shot groups in 2 grain increments and testing how they group at 300 yards. Want to know why I’m going with 7 shot groups? Check out this great article: Statistics, Shooting and the Myth of the Three Shot Group.
Alternatives to Audette’s Ladder Test
A drawback of the Audette Method is that EVERY shot is figured into the “ladder”. If your rifle is prone to vertical dispersion (due to poor bedding, stock flexibility, poor quality optics, etc.) you may never be able to find the sweet spot based on any process that evaluates individual shots. Simply stated, the normal dispersion of rifles that are less than benchrest quality will give false indications and overshadow any meaningful results. With benchrest quality rifles (Creighton Audette’s first love), the Ladder Method works extremely well. But it can be error prone for sporters and other less precise rifles. The use of a chronograph can help, but ultimately the ability to see how the bullets group on the target is also critically important.
There are a few alternatives to conventional Ladder Test developed by Creighton Audette that was presented here. A populate one is Dan Newberry’s Optimal Charge Weight (OCW) Method, which some claim is an improved and less error prone way to perform load development. Here are a few useful links to learn more about it:
Who is Creighton Audette?
Creighton Audette did as much for the precision shooting community than possibly any other figure in history. His engineering background and objective, data-driven approach gave new insight and helped bring clarity to this emerging field that is often clouded with strong opinions, myths, and gut feelings. Audette (now deceased) has been referred to by people who worked with him as “the best engineer that ever worked at Frankford Arsenal”. He shot on the US Palma Team, and won multiple National Matches at Camp Perry. Many of his articles were published in American Rifleman and Precision Shooting magazines, and are still considered to be the most advanced and accepted methods in the field. One of my favorite quotes about him is “he had more intellect in two of his nose hairs about rifles, shooting, and engineering than probably the entire shooting community today!” He was truly a pioneer in precision shooting.