Posted: 12/24/2014 12:46:27 PM EDT
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no real point here, just an imperfect example, shot today in the rain. obviously doing a ladder test at distance gets polluted as barrel harmonics and drop get mixed together, but i did it anyway, for no good reason.
I loaded 10 rounds very meticulously starting at 43.00g and going up by .10 exactly each round (except i'm an idiot and skipped 44.50g) Then i shot them in order starting from 43.60 and going up, then going back to 43.00 and going up. I was having trouble seeing the cluster of holes on the cardboard so i couldn't tell exactly which order the last 5 rounds were shot in. I think I know, but I'm not 100% sure so I just put them all together with their velocities. Also, I did not change my hold at all, including no compensating for wind, so i believe the horizontal is mostly wind. Couple interesting points... IME, when you get close to the max, a LITTLE bit of powder will make a BIG difference in velocity. But back off a few grains and changes in powder don't produce nearly as large an increase in velocity. During matches, I'm usually shooting these more than 100 fps faster. This is a pretty moderate load so you can see it doesn't change that much. In fact, for the 5 rounds from 43.60-44.00g the velocity varied only 8 fps. and only 3 fps from 43.80 to 44.00. Of course, with a sample size of one... and I don't have an explanation for the next 5 shots which are all over, though my eye was getting a little fatigued so i let a couple of them sit in the chamber longer than a minute while i blinked and tried to focus. another interesting note is despite varying the charge by a whole grain from 43.00 to 44.00, the 10-shot group was still sub-MOA and the vertical component is only 1.33" at 331 yards, which is well under .5 MOA according to jbm, the min and max velocities 2832 fps and 2901 fps should give me drops of 13.9 and 12.9 respectively, so exactly 1" vertical at that distance, ignoring bullet exit/barrel harmonics. shots 2 3 4 look pretty tight, 5 fps and only 2 bullet diameters of vertical. i'll make a few more of those and see if it is repeatable 
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I noticed your comment on " obviously doing a ladder test at distance gets polluted as barrel harmonics and drop get mixed together"
That is the whole point to doing a ladder test, to find the point at which the harmonics and velocity, thus the drop, give the least sensitivity to powder charge variation. Well, the good news is your shot fall looks good over that whole range of charges. If this were a HP Match rig, the performance was X ring capable for the rapid fire stages from the magazine. To do any better, you would have to move the distance out. Nothing wrong with this outcome in my view. If you are worried about more performance, you would want to move the test out to nearer the sonic transition distance and test again where the velocity difference starts to calculate as a bigger spread than your group size. |
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using your ballistic calculator, you can see that at 100 yards, a relatively large change in velocity would have a very small change on drop. thus, the difference you see on paper is the result of the internal ballistics/barrel whip, not gravity's effect over different flight times.
when you test from 300+ yards, you don't need a benchrest quality rifle to start to see the effect of gravity for different flight times. however, you still get the barrel whip, so sometimes slower shots can still end up higher on paper, though this is less likely as distance increases (and i'm shooting a fairly stiff barrel) |
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Here is a good video describing a ladder test very similar to what you are doing.
https://www.youtube.com/watch?v=yJKVc5z9WVM |
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A sample size of one yields no useful information.
Those small differences in POI at 331 yards could very well be unimportant, misleading and statistically insignificant. When I do a ladder test, I shoot 3 to 5 of each powder charge. I track both group size (accuracy) and POI deviations due to powder charge changes, as well as individual POI and muzzle velocity. I keep the targets. I photograph the case heads with a charge weight roadmap in the photo, so you know what you are looking at. |
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lefty, interesting video. i am doing coincidentally almost exactly the same test he is at almost the same distance.
he had some issues in his video that i see are already addressed in the comments (like the 'shockwave' speed of sound thing, and i have no idea where he got the idea that the steel changes size enough to affect the bullet) but overall it was pretty good. he even mentioned someone in the comments doing tests at .1grains like i am. the biggest issue i think though was saying NOT to do it at 100. as i said earlier, doing it at 100 means you're seeing what you want to see, which is the harmonics, not the drop. anyway, he also mentioned something that i should have known but apparently spaced out on... using the magnetospeed chrono will change the harmonics of my barrel... doh! so i have to go redo my test now without the velocity. this feels so heisenberg lol you can either know the position or velocity but not both and i had just done another 5 rounds today! i repeated the test again on the same piece of cardboard, just the 5 shots from 43.60-44.00 today from 529 yards. i couldn't see the holes from that distance so i don't actually know what order they're in, but the groups are sized and shaped remarkably similarly with one low and 3 almost completely horizontal. wind was blowing from the other direction today though. (again, i made no adjustments for wind) hard to read the calipers but it is about 1.8" of vertical and 2.5" total, so still 1/2 MOAish from 500+ yards i need a better aiming point for the next test too. that dot is a little too difficult 
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| I would be pretty happy with that. I like to use an orange dot for my aiming point especially at 500 yards and beyond if I'm shooting for groups plus I'm using a fixed power scope with a fine reticle. I've seen enough of your other posts and know that you are a very good shooter. There couldn't have been much wind if you were hitting that close to your aiming point with no adjustments. |
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Thanks yeah not much wind. My 10mph full value is .7 mil which is about 12-13" at that distance. Iirc the wind was running a little at the target enough mirage read right to left but turned at me somewhere in between. Kestrel said 4-6mph right in my face so no value.
Wind was steady enough I was 4 for 4 on a 1 7/8" ruler at 600 that I've been tying to hit for weeks. 3 of the hits were on the washer around the bolt too. Btw I was using the vortex gen 2 on 27x With that .06 mil gap. At 100 and 500 yards it's annoying but at 300 it is perfect size for the 5/8" shoot n see dots |
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Quoted:
Thanks yeah not much wind. My 10mph full value is .7 mil which is about 12-13" at that distance. Iirc the wind was running a little at the target enough mirage read right to left but turned at me somewhere in between. Kestrel said 4-6mph right in my face so no value. Wind was steady enough I was 4 for 4 on a 1 7/8" ruler at 600 that I've been tying to hit for weeks. 3 of the hits were on the washer around the bolt too. Btw I was using the vortex gen 2 on 27x With that .06 mil gap. At 100 and 500 yards it's annoying but at 300 it is perfect size for the 5/8" shoot n see dots I'm determined to be as good as guys like you eventually. I'm thinking I read before you compete in long range matches. How long have you been shooting long range precision? |
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heh, you can be a lot better than me, i'm sure!
i shot for 5 or 6 years in CMP and NRA High Power. didn't start shooting tactical/sniper/field style matches until 2010. Since the first winter mammoth in 2011, I've shot or been match director in 37 matches. I hope to make 5 matches this year if work permits. Only made 2 matches last year so really looking forward to shooting next year. heck, i even practiced in the rain this week. really rusty on barricades these days |