ladder test questions

[spencerhenry]

i have been loading for 24 years and have developed loads in many calibers in many rifles and been satisfied with most rifles, others not so much. recently i have was trying to find an accurate load (sub moa) for a kimber 8400. i worked at it the way i always have, load 5 rounds of each load varying the load by 1.5 grains or so, when that doesnt show promise, change bullet, when that doesnt show promise, change powder. nothing i loaded ever produce better and just under 1.5 moa. i gave up on that kimber after finding out the kimber doesnt have an accuracy guarantee, and that their requirement is a 2" 5 shot group at 100yds. so i bought a brand new cz model 3 in 300wsm.
day one i sighted it in with 5 rounds of ammo loaded for the kimber, then shot a 5 shot group with the load that looked best in the kimber. the group strung out left to right, i am not sure why, but suspected loosening action screws or scope mounts. not having any tools with me, i continued with my ladder test. it consisted of 10 rounds starting at 62gr imr 4350 and going up to 66.5 grains in .5 gr increments. i shot at 200yds because at this time of year that is the only range i can comfortably set up. loads 1,6, and 8 grouped together with under .25 minutes vertically. loads 5,7,9, and 10 grouped about 2" higher with about 1.25 minutes of vertically dispersion. loads 2, and 3 were virtually identical vertically, and about .75 minutes above loads 1,6, and 8. it would appear that i have two "groups", the higher group is 64, 65, 66, and 66.5 grains, and the lower group is 62, 62.5, 63, 64.5, and 65.5 grains. 62, 64.5, and 65.5 are within 3/8" vertically making those three the closest together. 62 grains is too low of a load for the purposes of this rifle so now i am at 64.5 or 65.5. is the next step to load in .1 gr increments around 64.5 and 65.5, or work around 66?

[Tim K]

Somewhat screwey data there with #8 being so far outside 9 and 10. I'd probably assume you slapped #8 and work the high side. Any signs of pressure at 66.5?

[spencerhenry]

i assume by "slapped" that you mean it was shooter error?
all shots were from sandbags, all shots felt good, rifle really seemed to just hold point of aim easily, that is not to say it couldnt be me, some days i wonder if i can shoot anymore. i have a 4.5-14 long range side focus leupold on it.
the interesting thing is that the even grain loads from 64 on up hit in the high group, the 1/2 grain increments of 64.5 and 65.5 both hit in the low group. after further thought it looks like the higher end of the test shows some promise as well as the bottom end. with this being a hunting rifle for big game, i am not interested in a low power load even if it is accurate. i had no signs of high pressure with 66.5 in this rifle, in the kimber i ran 67gr and that was starting to show high pressure. my manuals vary tremendously even from one printing to the next from the same manufacturer.
i think i will do another refined test at 66 to 66.8 maybe. and then another one around 64.5, and try to run the distance out to 300 or more. it is tough to find a place without lots of snow where i can shoot that far without driving a long way.

[Tim K]

I did mean shooter error. I'm not a great shot, but I am learning that I sometimes can not detect when I am the problem.

"the interesting thing is that the even grain loads from 64 on up hit in the high group, the 1/2 grain increments of 64.5 and 65.5 both hit in the low group."

Your above statement points to shooter error to me. Again, I'm no expert, but that's what it looks like. Seeing a high and low group is common, so I think you're on the right track with your reasoning for selecting the high group.

Stretching the range is a good idea, go as long as you can.

I haven't done this, but I think it's a great idea. If you have the patience, load up two or three at each charge weight. That ought to help weed out any shooter error.