There are lots of ways to find loads. However, we have to separate load development from POI shifts due to conditions. We frequently miss changes in conditions at long range. Everything may look the same, but they most assuredly are not.
There have been times I have watched the wind flags reverse in the middle of a group for record, and I was sure I was strung out across the target--only to find I was centered. There have been times when I thought I had the wind nailed, held on the edge of the target, and found that I shot a decent group right where I aimed at the edge of the target. Now there have been times when I get it right, but I am 50/50 at best at precisely reading conditions.
There is also natural dispersion. My hammer 300 SAUM IMP heavy gun--that has shots lots of screamer groups and won group aggs and score aggs, doesn't shoot 4" 10-shot groups at 1000 yds all the time. In good conditions is usually shoots 4-6" 10-shot groups. In poor conditions It should hold under 7-8".
Relay to relay, there can easily be a 1 MOA POI shift. That shift is due to conditions, not the load.
So what I do is find a load that repeats in good conditions, get centered, then read conditions to the best of my ability to stay at the center of the target. In a match we get sighter rounds to find the center of the target.
I use the same approach with a hunting rifle, albeit with much looser standards for group. After all, the kill zone on a deer is what, 14", which is larger than the 9 Ring. Also, a hunting rifle isn't as stable to hold, doesn't track well, and doesn't handle harmonics as well.
However, the same principles apply. I find the load in good conditions, then work on reading conditions. Here is an example of a load I just found.
I have this 33-28 Nosler on an FN built "New" Winchester M-70. It has a #4 contour barrel and sits in a Bell and Carlson stock. I built a few years ago--well before I started working at UM. I chambered the barrel myself and intended for this rifle to be an under 600 yd carry rifle for hunting elk in the Oregon Cascades and Coast range.
Well
@Ryan Avery told me I had to be able to shoot 800 yds to be able to hunt in the places I needed to hunt here in Idaho and Montana. So I decided to see if I could get this rifle to do that.
I opened up the action to take a Wyatt's box and sorted out he feeding and ejection. I throated it longer, cut a +P throat, and installed a brake. (I did all this myself at home.) I also pulled off the short range scope and mounted a Sightron 6-24 scope
I had laying around.
This is not remotely like we build long range hunting rifles at UM, and it's not what I recommend. However, all my real time and money is tied up in my competition rifles so I went with this rifle.
The biggest problems with it are that it's on the light side for shooting a 300 grain bullet at 2800-2900 fps, the stock isn't a good one to control the twist of such a rifle, and the barrel is a little lighter contour than it should be.
I started out shooting two-shot groups at 100 yds to find what didn't work. I shot a couple three shot groups of what was promising, then went to 650 yds for real load development.
I shot 3 or 4 3-shot groups that were 5-6" at 650. I noticed the ES was in the low 30s. This was with new brass was necked up form 28 to 33 cal. I was checking powder charges in 1/2 grain increments, so this group size was holding over a grain of powder or so.
I decided to check with fire-formed and prepped brass. I wound up taking out 1.5 grains of powder with the fired brass, which brought the velocity back down to where it shot the best with new brass. Final group was 4.375" at 650.
Now that doesn't meet UM load dev standards, but I happen to know that 4-6" groups at 650 easily make this an 800+ yd rifle. If I was motivated I could keep working, change powder, and maybe tighten up the groups. Although it is hard to hang on the this rifle when I shoot it....
So I am confident that this load will hold together when I take it hunting next month. This isn't the first time I have done load dev this way. I will get out and shoot it at various distances to make sure my ballistics are dialed in. If I miss it won't be because of the rifle.
When Nick does load dev for our company rifles, the process is similar except he keeps at it until the load is under 1/2 MOA at 650 yds. He gets these loads to repeat. Whenever we recheck the rifles we have found loads for, they shoot the same. Five shot groups also stay under 1/2 MOA when we have tested those.
So three-shot groups at 600+ yds do indeed work to find good loads.
And yes, I am building a rifle more suited to long range hunting here. I almost have it done. It's on a trued New Haven M-70, has a Benchmark carbon wrapped barrel that I dialed in to near perfection before I cut the chamber. I also opened the action for a long Wyatt's box, and it sits in a much better long range style stock. It's in 30-28 Nosler. I plan to shoot Hornady 225 ELDMs.
If I ever decide to build a big 338, it will be on a Vesper. As much as I like CRF M-70 actions, they are a pain to rebarrel and open up......although my CRF M-70 in 416 Rem is what I am taking to Africa later this year for cape buffalo.
