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Very first ladder test, please take a look.

7K views 20 replies 5 participants last post by  unclenick 
#1 · (Edited)
I know this isn't much to go on. I'd like to hear your thoughts anyhow. If this was the only info you had, which load would you use? Where would you test next? Two more ladders using same loads for comparison? Between 3,4,&5? Between 11 and 16 somewhere?

I wa unable to put the pic on here, so bear with me while I explain results.

270 win, RL-19, 140 sst, 325 yards, 55 degrees

Charges: 1-17= 52.6 - 57.4 in .3 increments.
Started with three foulers and one sighter.

shot 1 & 2 same elevation, 3 inches wide
3,4,5 same elevation (up 2 inches from 2), 7/8" group!
6, up two inches from 5
7&8 same elevation, up two inches, 3 inches wide
9 up 1.5"
10 up 1"
11 up 1"
12 up 3/4"
13 down 1.5"
14 up 2.75", left 2"
15 down 1.75"
16 up 1.25"
17 up 2,5"

14's kind of the wild card.

I don't have a chrony yet.
 
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#3 ·
Can someone point me to information on the use of ladder tests and their interpretation? It appears to be simply a string of shots with an incremental increase in powder charge. Since there is only 1 shot at each charge, how does one know that some extraneous factor has not caused the "flyer" of a given shot in the sequence? Shouldn't the sequence be shot at least twice to check for this? The ladder test looks useful, but I would like to get more information on it's application and interpretation.
 
#6 ·
grit - over the weekend I load 15 rounds for my 243. Top end 44.0 grains and whatever 14 loads down in 0.3 grain increments equates to.

What was your shooting distance? I think 300 yards is the recommended distance because it will provide adequate separation between shots no matter what the load. The other question begging to be asked is how did you mount your gun? The ladder test requires NO movement of the gun between successive shots and the integrity of the data is highly reliant on the barrel being positioned exactly the same for each shot. All I have is a Bull's Bag rest, don't know if that is a sufficiently secure mount or not but outside of a butt bag I'm not sure what else I can do to lock the gun down in position.
 
#7 · (Edited)
Grit,

Load 4 is the obvious candidate because it looks like you could charge your cases ±0.3 grains with impunity. Set your powder measure to that and see if that doesn't do it for you. Good show!

Also consider trying some 0.1 grain charge increments between levels 11 and 14. It is frequently possible to pick up a sweet spot as the barrel vibrations transition from rising to dropping POI with increasing charge. It looks like you may be on the cusp there of another, albeit smaller, sweet spot there.

The next thing you have to do is try your sweet spot loads in different shooting positions to see which is most immune to shooter variation? That'll be the one to run with!

Nick
 
#8 · (Edited by Moderator)


Here's a pic of the target. Range was 325. I Shot off a rest you put the rifle in. Not perfect, but good.

Light gusty breeze was blowing from about two o clock. The breeze died around shot ten. I believe most of the horizontal displacement is due to the wind. I didn't try to hold for it.

I'm guessing I pulled 14 a bit. I'm further guessing it should've hit near 12. I've loaded six rounds of four, thirteen, and fifteen. I'll shoot two threes for each. We'll see what that shows.
 

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#10 ·
flashhole said:
Super photo, were all shots aimed at the orange target?
Yes.All shots fired at the same point of aim. I did not try to hold for windage. I got to wondering what point fouling will become an issue. I know all guns will be different, but take a guess for me. How many should I shoot before cleaning while accuray testing / load development? Ten? Twenty?

For the test, I shot three foulers, then all 17 charge weights. Should I have stopped to clean in the middle?
 
#12 ·
I do all I can to reduce margin for error. I considered shooting three of each at seperate targets.

There is an extension of the ladder test called Optimium Charge Weight. He recomends having a target for each charge weight. You then shoot one round of each weight at its target, and repeat until you've shot a group for each weight. This spreads the variables through the whole test. It also give you group centers instead of single shots to compare.It also shows grouping.

As I had 17 charge weights to test, this would be a **** of a lot of shooting, and an all day project. I believe the single shot test gave me good places to start, with a minimum of shooting.
 
#13 · (Edited)
Grit,

I did a little more work on your ladder target. It is usually a bad idea to throw away a data point, such as your shot 14, without a very substantial justification, and this analysis winds up showing why or simply that it didn't help to do so.

What I did first was take the camera angle distortion out of your target in Photoshop. I then pasted that into a CAD program and used the measuring tape in the image to scale a pair or rules with 0.1"� minor divisions to facilitate locating the bullet hole centers for data entry. I located the vertical and horizontal scales so their zeros are at the bottom most and left most holes positions, respectively.

Next I wanted to get some kind of indication of how repeatable your bench hold was? Horizontal and vertical group size are not interchangeable because wind and barrel vibration affect the two differently. But since you hadn't yet identified an accuracy load to group, the only indicator available was the extreme spread of the position of the horizontal holes fired after the wind died down. I made a circle of that diameter and centered one over every hole location. This means the hole could have been made anywhere within that circle, though the probability gets lower out at the edge. Nonetheless, you can see (images below)shot 14 could have fallen much closer to a horizontal line with 12 and 13 and 15 if you put it at about 4:30 on the circle. Since that is within the hold circle guess, you don't know that it would not have been an accurate load?

Going to the graphs, I first plotted horizontal and vertical dispersion connecting the holes (yellow line) so the firing order was more apparent to the eye. I then plotted spline curves both including (red) and excluding (blue) shot 14, and you can see, even though shot 14 adds a bend, the trend line you would eyeball through the middle isn't too different. I also used the most extreme horizontal position jumps (2, 8, 12, 14, and 17) to pick shots to eliminate, on the assumption this was an indicator of a wind gust or a shooter induced error (heartbeat coincident with shot break, etc.), and plotted a spline curve that skips all these points (brown). This line is much smoother on the horizontal and appears to reveal the wind trend, moving the shots to the right as the wind drops off. When I went back and plotted a spline curve of this same edited shot population on the vertical, it, too, is smoother, but still not really affecting the overall trend.

You will note that shots 2, 8, 12, 14, and 17 deviate in opposite directions in about equal quantity off the horizontal, so this is why the trend error tends to cancel out. Moreover, despite the shot count being too low for great confidence in the results, it is nonetheless an indication that the error in dispersion is random.

So, I concluded there really wasn't any good reason for eliminating any of the shots in the ladder. All seemed to fall within reasonable random error expectation. So, the final graph is a least squares 5th order polynomial fit of the vertical dispersion for all 17 shots I did using Mathcad's regress(vx,vy,n) function. Higher order polynomial fits are tricky, because you can start forcing data fits that aren't real. However, in this case the 5th order fit had almost the same shape as the 4th order fit except it reduced a vertical offset from the first and last shot. It also eyeballed through the middle of the shot 12-15 range better. So I deemed it a legitimately better fit. Third order and below didn't fit well.

The surprise is that the sweet spot looks like it actually fell between shots 12 and 15 in this ladder. This represents a 0.9 grain span of powder charge. I have had bullet and powder combinations that remained accurate over a ±1¼ grain charge span in a .308. The same rifle with the same powder proved accurate over only a ± 0.2 grain charge span with a different bullet weight. So you have to figure out whether the trend lines and data here had enough resolution to get you where you want to go? I would not only try firing 10 rounds at a charge weight in between the shot 13 and 14 charge weights (as labeled on the graph), but I would also fire a new ladder starting at the shot 12 load, and incrementing the charge in 0.1 grain steps up to the shot 15 charge weight. Let's see what happens in the middle?

You could also run a ladder of 0.1 grain increments in the shots 3-5 range to see whether that is a real or a random shot bunching? While the data arrangement I put together here looks promising for shots 12-15, the 0.3 grain increment may just be lacking enough resolution, which would throw these results off (you could have other sweet spots hidden within these if you are on a tight spot, though having one that tight isn't very useful for practical conditions of changing temperature).

A final comment on benching: It isn't as easy as it looks like it should be to get good bench rest results; not even with all the right equipment. A sporting weight rifle in particular may not vibrate the same way in human supported positions as it does of the bench. How much difference it makes is load sensitive. So if the gun is for field use, take Boots Obermeyer's advice and check the loads in real shooting positions to see what groups best for you there, as well? For a given rifle, some loads will be more consistent between the bench and field positions than others, or even between different field positions. It is worthwhile trying to develop a position-insensitive load for the field. Besides, this means getting to buy more bullets and powder and do more shooting.

Nick





 

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#14 ·
Uncle Nick, Thanks a ton! Nicely stated, and illustrated! I have loaded at 4, 13, and 15. I will add the loads for 13.5. Weather permitting, Ill shoot them tomorrow. Wish I had a cad program.

I saved your graphs for my notebook. I'll post the results. We'll see how they pan out.

Once again, Thanks!

P.S. I have more guns. Oh, one more question. Ladder tests for handguns (6" revolver)?
 
#16 ·
Finally got to shoot! Who's guessing? I shot two threes of each load.

#4: .76 & .6

#12.5: .93 Didn't shoot another.

#13.5: .32 & .29 !!!!!!!!!! Also, if I overlay them, the group doesn't grow.

#15: .47 & .62

I might play a bit between 13.5 & 14.5. Awesome to get results on very first try. Thanks for all the help! Especially Uncle Nick!

Back to the bench!
 
#19 · (Edited)
Grit,

Congratulations. Looks like you have a shooter! I would still run a ladder or groups of 3, at least in the 12.5 to 15 shot load number range in 0.1 grain increments. The reason would be to learn how wide that sweet spot really is and where its exact center really is? It would be nice if it turns out to be a wide enough span (0.4 grains or more from low to high weight) that you can just throw charges through a powder measure, and not have to weigh them. Measures have the advantage over scales that a particular lot of powder's characteristics won't change much with volume, but they can change with moisture content for a given weight. In other words, if the powder gets exposed to big swings in temperature and humidity, you may have to adjust charge weight (more load testing), but the measure settings are likely to be stable. This is why you see bench rest shooters using measures rather than scales at the range. It isn't because they can't afford a wind shield for their scale.

The other reason for learning the span ends is be able to try loads near the outer edges of the weight band as well as in the middle to see if these loads exhibit differences in shooter position sensitivity, as I mentioned earlier. In the mean time, close your powder container tightly between uses until you have all your data and measure settings established. We don't want it changing weight on you before then!

Enjoy the rifle!

Nick

P.S. I've never tried ladder testing a pistol. Usually they aren't accurate enough to use a ladder reliably. Some of the single-shots may be an exception. The best benched group I've had was 0.37" C-T-C at 25 YARDS from a newly fitted 1911 in .45 ACP. This theoretically means an inch and a half at a hundred yards in perfect conditions. Perhaps a ladder at 100 yards would have worked when that gun was young?

That said, there is a purpose issue. I was shooting that gun in bulls eye competition. It got that accuracy with 4.2 grains of bullseye under a 200 grain Hornady JSWC, but I stll shot a lot of 3.8 grain loads under 185 grain cast bullets through it. The drop in accuracy (groups opened to about 1.25" at 25 yards) would still score in the X-ring from a rest and the reduced recoil was an advantage in recovering the sight picture between shots during rapid fire.
 
#21 · (Edited)
Oops! Moved a decimal point. Fixed.

One last tidbit. I dusted of my calculus and applied derivative testing to the least squares fit. The second derivative crosses the 0 axis where the first derivative (not shown) was at a minimus and changing direction. Rather than shot #13 + 0.15 grains, it crosses at shot #13+ 0.13 grains. Close enough to shot #13.5 so the difference isn't a practical adjustment to make. We're down in the noise here. Nonetheless it will be interesting to see what Grit's 0.1 grain ladder reveals?

Nick

 

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