Hmmm... Interesting, but the Audette Incremental Load Method, explained nicely by Ralph Constantine, presents some very real problems that I’ll try to elaborate on. I do use my own "version" of Ladder Load Development that I'll try to quickly explain, and I use it often to develop custom accuracy and best-velocity loads for my customers.

The problem with using only lone load and shooting it in sequence at the same target is this: The author of the article, I’ll call him RC for short, is assuming and minimizing some elements that should not be minimized! (though I’m sure when he uses this method it works well enough for him with a typical BR rifle...).

1: That heating of the rifle barrel has no significant cumulative effect in a rifle string.

2: That the vibration effect is limited to certain directions and amplitudes.

3: That round-to-round load variations are insignificant (which yes, may be far more true in a dedicated BR type of ultra-accurate rifle.)

(I'll pause here to note that RC is probably talking about high precision match type rifles. In that case, slight changes in load properties will produce detectable and somewhat more uniform variations in impact point. But we're talking about the somewhat wild and wooly M1A platform, which has it's own very real idiosyncrasies that we've all discussed here.

My own BR rifle, a Wichita-actioned rifle in 6BR, with a rather heavy 28” stainless steel Douglas ultra-match bbl, won’t shoot any reasonable load into more than 0.8” @ 100 yds. My load “devo” work was thus in the measured ranges of 0.01” variants. Modern BR shooter types are measuring loads down at these micro-variant levels. Fun, huh? I could pick off an Ork’s earlobe @ 400 yds with my BR rifle… which would undoubtedly make “him” think twice about further advancement towards my position…)

3: That groups might be visibly grouping as his did , again, in the M1A platform. In my experience, this is not the case. The groups in a battle rifle, or even an accurate hunting rifle, often scatter all over the map (relatively speaking), with impact points on a hotter load potentially impacting below the lighter loads.

Why all this? Because the barrel vibrations RC explains do indeed occur, but they are not so consistent, again, in a less-rigid and well-behaving “barrel assembly complex” (Oohhh! A new acronym: BAC™! Yeah!) such as we typically have in an M1A rifle.

As well, in a rifle platform with a tightly fitting stock located under it, differential barrel heating occurs within a relatively short time in a load string. This means that the rifle bbl losses it’s upper-side heat faster, where it’s totally exposed to ambient air, than it does down where the growing heat of continued cartridge ignition is trapped between the stock and the bbl. Thus, the bbl tends to bend upwards from differential thermal expansion, even if you use a constant (i.e: non-varying) load.

Try this: shoot 20 rounds at about 1 round every 10 - 15 seconds. Watch your group size open up, but also: climb up.

Then, vibration of the muzzle end will almost always be in a “various” pattern, not just up and down, As RC noted, this is called a Lissajous figure, and it’s what you’d probably expect to see in an oscilloscope fed a mixed signal. This explains it well:

http://en.wikipedia.org/wiki/Lissajous_curve

Given such impact point variations, picking one good load out of the resulting mess can be quite daunting.

My variations include these key points:

1: I do load 3 to 5 loads of each specification. This minimizes, or at least averages out, group load variations such as brass thickness, neck tension, even bullet-to-bullet dimensional, weight and/or CG variations. Plus, the ambient conditions downrange ALWAYS vary by small but potentially impact-point deflecting amounts.

Small stuff, yes, but cumulative as well, especially if we’re measuring at 0.10” increment levels! It’s always best to average these out as much as possible, right?

2: I use a target I’ve developed and printed up on Tabloid sized paper (11.5 X 14). For this sort of work, I’ve created a target that is easily visible out @ 200 yds, but has 4 to 6 targets on each paper. (I have both 100 yd and 200 yd variants right now… 6 targets for 100yd, 4 for 200 – 300 yds. For example, this target size allows me to capture a group size of up to ≈ 4” in overall diameter.

Each target on a given sheet is also numbered with an easily seen indicator. I then e-mail the graphic to my local Copy Shop and then go pick ‘em up, by the dozen or more, all at about 20¢ each.

3: I advance my target by one for each load. Incidentally, you could also use this same approach with RC’s ILDM. Shooting at ‘the next” target in the series, but holding the same center of target hold, will then produce a single bullet hole target which should be just as valuable as showing 20 impacts on one target
(I’m talking right now about his ILDM, not mine…) but without the drama of trying to pick out and number each additional on-target hole! Ouch!

Of course, if you are doing a grouping average using 3 - 5 shots, you could also hold your shooting down to, let’s say, 4 or 5 loads before moving on to a clean sheet.

BTW, by using a different target for each load group, (or even for each individual round if you are using the IDLM) you can most certainly then reduce your target range to 100 yds and still see any significant differences in impact point.

Of course, things do change with a bullet en-route out to 200 or further ranges, and it’s always good to increase the range to better see those effects. But where I live, it’s also damned-near impossible to have a windless day, and the longer ranges just multiply those effects.

4: I allow my rifle’s bbl to cool down to a near-ambient temp between shot groups. This is certainly what happens in the hunting field, where we’re not pre-fouling the bbl, or are sitting out there for a few hours to get that one- or two-shot firing event (most hunting target species will not generally stand about for more than 2 attempts on their lives!).

5: Of course, for match shooting of your M1A, you should pre-foul the bbl with (in my opinion…) 2 – 3 rounds, but then, let it all cool down before commencing with your load development work.

6: My usual load increment, initially at least, is typically 0.5gr, starting down by, as RC nicely explains, the anticipated accumulated “decrement” (a new word to me, I'll admit!). so, a total load buildup from, say, 39 gr of Varget on up to 41 gr, will net me 5 different loads.

I have used lesser increments with subsequent fine tuning, but I'd also hope that my battle rifle is not so sensitive to a 0.2gr increment that this alone would significantly alter group size.

7: I do fire off all 3 or 5 rounds within a specific load group in as fast a sequence as I can accurately accomplish. I do try to shoot fairly fast, as per my long-range target instructor’s ideas way back in my Canuck Army Long-Range Shooting Team days.

This minimizes accumulated and instantaneous muscle fatigue, plus any heat buildup effects. (bbls react over time to heat, and thermal changes are insidious!)

8: I chrono all my loads. I then plot the following three important graphs: I start with velocity versus load (VvL). This of course initially ignores accuracy, but it’s critical becasue I simply don’t want to overcook the load, especially in a rifle like the M1A which does not respond well to the highest possible velocities that you can possibly create with, say, a 175 gr bullet. It has it’s functional structural limitations.

Having assured myself that I won’t Chernobylize my prized SAI NM rifle, I then note group size versus load (GvL) and group size versus velocity (GvV). By then comparing the last two (given the limitations imposed by the first VvL graphing), I can quickly see which load has produced the tightest but also the best, velocity stats.

9: Some additional details: I don’t usually go beyond 5 different loads in a series. If I don’t see any typical positive and/or promising group size relationships within that series of some 5 incremental loads, I’ll probably at the least change my powder type.

Once a reasonable initial group size has been found with a particular powder, this method can be used to try other variants within that load, like bullet seating depth, the bullet type itself (a very big factor, I’ve found…), and bullet seating concentricity.

More recently, I’ve been fiddling around with neck annealing and primer type, though that has typically had the very least impact on any of my loads in well over 45 years of reloading! CCI and Winchester primers have served me well. Perhaps there remains some untapped variables in primer types? I may also run out of time, before I go for my big dirt nap [or, in my case, conversion into a hydrocarbon haze …]

Well, there it is. A modified version of RC’s Audette ILDM for sure, but with more attention to real-world variables, and not requiring of a longer target range to see differences in impact points.

It can also point out certain typical rifle-based issues, like loose or poorly fitting receiver and/or bbl bedding, a bad muzzle crown, a bad barrel, a loose or non-concentric chamber, bad scope or sight mounts, and so on.