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Normal Topic First Time Ladder Testing - 260 rem (Read 883 times)
Nak
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First Time Ladder Testing - 260 rem
Mar 15th, 2018 at 9:16pm
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With my new 260 I decided to try something different with working up a good load. My method to date has involved loading up 4 or 5 loads per powder charge with increments of 0.5gr ,starting about 1/3 of a way up between book min and max and then shooting groups, going with whatever gets the tightest and then finetuning from there. That method has worked well for me to date, but can be a fairly long process.

This time I thought I'd try a ladder test, shot at around 285m - image below

Loads 1-6 ranged from 37.5 grains 40gr of 2208 with a 120gn ELD-M. I shot the loads 1 through 6, and then shot the same over a chronograph - Velocities seemed reasonable out of a 21.5in barrel

Velocities

1- 2751
2- 2759
3- 2808
4- 2845
5- 2878
6- 2923

With no real tight cluster of groups can anything be interpreted from this??....Velocities were around what I was after with loads 4 and 5 and they are the closest so I was going to load up a few more of those charge weights and see what groups look like. Any other interpretations would be appreciated...

IMG_2874 by nak _80, on Flickr
  
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JaSa
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Re: First Time Ladder Testing - 260 rem
Reply #1 - Mar 15th, 2018 at 10:05pm
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In a ladder test you should look for the most shots at the same vertical location on the target (which you don't have) and not the tightest group. So not to sure where to go from here, sorry.


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JaSa
  
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Re: First Time Ladder Testing - 260 rem
Reply #2 - Mar 16th, 2018 at 7:30am
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I agree that sideways dispersion is a pain and confusing, how about ignoring it (pending a better result with, say, a repeat trial) and just measuring the verticals, using the loads in the middle of the string with the least separation in the vertical plane as a secondary starting point for further load research/development.
  
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Re: First Time Ladder Testing - 260 rem
Reply #3 - Mar 16th, 2018 at 9:59am
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I get much better velocity with H414 rather than AR2208 in the 260 Rem  Wink

The ladder test seems to defy the rules of statistics to me (and I use stats a lot in my day job). What size group can you shoot with this rifle? Now consider whether the differences in a single shot with each powder load can be considered significant or are just a product of random variation (or barrel warming). Shoot 3, 4 and 5 again and they might look completely different. FWIW, I would go back to your old method unless you can be confident of putting successive shots through the same hole.
  
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Re: First Time Ladder Testing - 260 rem
Reply #4 - Mar 16th, 2018 at 11:08am
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Try loading 3 rounds each of 3,4,5 and see how they group,
I've been starting five 1/2 grain steps below book maximum
and loading 3 rounds of each usually get a good result with 15 rounds it's easier than a ladder test and can be shot at 100 or 200
metres just do the fine tuning at longer ranges.
  
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Nak
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Re: First Time Ladder Testing - 260 rem
Reply #5 - Mar 16th, 2018 at 1:31pm
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MeatHunta wrote on Mar 16th, 2018 at 9:59am:
I get much better velocity with H414 rather than AR2208 in the 260 Rem  Wink

The ladder test seems to defy the riles of statistics to me (and I use stats a lot in my day job). What size group can you shoot this rifle? Now consider whether the difference s in a single shot with each powder load can be considered significant or are just a product of random variation (or barrel warming). Shoot 3, 4 and 5 again and they might look completely different. FWIW, I would go back to your old method unless you can be confident of putting successive shots through the same hole.



Interesting comment - I was miserable at stats at uni, so are you able to explain that a bit more for me. Ignoring the fact it is only a single ladder test with no replicates, I would have though that the relatively consistent incremental vertical increase in where shots landed higher each time corresponding with increased powder load and velocity would be more easily explained statistically compared to say a more random clustering of shots ???

But, like you said with no repeat, it could be completely random and just  result of human error, barrel warming etc. Although I did allow the barrel to cool between shots, shot off a bench and I'm usually a reasonable shot.  I haven't shot any groups with this rifle yet, just 10 shots to run the barrel in and get the scope zeroed and now into this.  I think I'll load some rounds at loads 4 and 5 and see how it groups rather than repeat the ladder.

I had plenty of 2208 on hand so I thought I'd try that - I was surprised with the velocity, it was better than expected. Interesting the run in loads were with 2213sc and velocity was really slow down around 2600 at close to ADI book max.

  
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MeatHunta
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Re: First Time Ladder Testing - 260 rem
Reply #6 - Mar 16th, 2018 at 3:13pm
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Yep, the trend is correct, and is more reliable than comparison of differences between any single pair (or triple) of shots. Of course, the latter is precisely what the ladder test relies on. Even if you can shoot inch groups all day with this rifle (and you don't know about the rifle yet because it's new), the ladder test has next to zero statistical power. How much did you let the barrel cool each time? Was it the same temperature each time, or maybe getting progressively warmer? It's a new barrel, so you're knocking more edges off with each shot, it may take a few to settle in. IMHO, there are just too many variables/unknowns in the mix to rely on the differences between where any two shots land as guidance for your optimal load selection.

AR2213sc is OK for bullets from 130 grains and up, but is too slow burning to get the best performance from 120 grain bullets. AR2209 burn rate is between AR2208 and AR2213sc.

In my rifle with 120 grain bullets H414 gets:
* 100 fps more than Benchmark 2
* 200 fps more than either AR2209 or AR2213
* 350 fps more than AR2208
  
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Nak
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Re: First Time Ladder Testing - 260 rem
Reply #7 - Mar 19th, 2018 at 8:13pm
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OK. I get what your saying now - a single ladder test has little value to put too much reliance on to due to the inherent possible errors and variables on each shot.  Yep, after going through the process I agree - for confidence it's either multiple ladder tests or mutliple groups, I think I'll go with groups. I'll shoot some groups with those loads 4 and 5 and fine tune from there. 

2208 seems to be getting decent velocities from this barrel with this projectile, and I would be happy with if i can find a nice accurate load, but it would be interesting to see what H414 would bring.

  
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Re: First Time Ladder Testing - 260 rem
Reply #8 - Mar 25th, 2018 at 7:53pm
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wasting your time doing a ladder test with one round per load. You can easily have 20-50 fps variation between loads (particularly between accuracy nodes) in a 3 shot group, so shooting single shot at each load tells you nothing as your velocities can overlap between shots. E.g

load 1: 40.0g say 2750 -+30fps  = 2720-2780
    assume you have a fast shot so 2780

load 2: 40.5g say 2780 +-30       = 2750-2810
    assume you have a low shot  so 2750    

so your second load, with more powder give you less velocity than first load.

Shoot 3 or 5 shot groups at 0.5g increments, then do a coarse seating test (20, 40,60 tho jump) to find a good seating depth, then fine tune power with 0.3g increments, then fine tune seating test (5 tho increments either side of best coarse result)

I load up 6 rounds with each load, shoot 3 shot group form lowest to highers, then go back shooting second 3 shot group form highest to lowest. This way you have two groups for each load so you can see a lot more trending between loads.

With the 260, I found 2209 gave tighter groups than 2208. 2209 uses extra 3-4g of powder compared to 2208 for same V.
  
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Re: First Time Ladder Testing - 260 rem
Reply #9 - Mar 26th, 2018 at 12:53am
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I like that 6 is fast and directly  (almost) above the target. I would slap a few of those through again as well.
  

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Re: First Time Ladder Testing - 260 rem
Reply #10 - Mar 26th, 2018 at 7:50am
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The whole point of a ladder test is to find a load that groups close over a range of velocities. It is to give you a quick indication as to where to start focussing your efforts.
  
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Re: First Time Ladder Testing - 260 rem
Reply #11 - Apr 2nd, 2018 at 7:33pm
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Did you not get the information you were wanting on the other site?

Best to have read up on the purpose of a ladder test before performing one and trying to interpret the results, so this is what you need to know:

The theory is that if you have a perfectly rigid barrel & action, then the points of impact will rise monotonically up the target with increasing velocity, since the time of flight shortens. There will be no lateral trend in this ideal scenario.  Please note the comments from the others - that this ideal pattern may be masked by inconsistency in the shooter, the rifle, and the ammunition may not shoot proportionally faster with increasing powder charges. The variation in all of these may mask this pattern. For many shooters & rifles, a ladder test is a complete waste of time because of these factors, and some others not mentioned such as insufficient shooting distance. These may completely mask any useful data. In cases like this the shooter may jump to an erroneous conclusion and becomes worse off than if having not performed a ladder test.   

Now change the barrel to one that for want of a better term "whips" when the rifle is fired. Superimposed on the above described vertical pattern is a second pattern, characteristic and individual to your rifle.

The purpose of a ladder test is to find so called "sweet spots" where these two patterns superimposed on each other, cancel each other, and the point of impact remains much the same over a range of powder charges. Lateral movement cannot be cancelled.

The value of finding such a range of powder charges is that you can nominally load your ammo for the middle powder weight, and then small differences in charge weight - and also things like neck tension, bullet weight variation, case capacity etc that alter barrel time - will hopefully result in less vertical distribution than might be the case in the theoretical rigid barrel, due to cancellation from opposing trends. In other words when operating at a node then reloading practices can be somewhat relaxed.

If you are very consistent with your reloading in respect of all aspects that affect muzzle velocity variation, in other words your ammo shoots with very low ES, then there will be little value in the ladder test. It may also not of much value for rifles where the barrel does not "whip" much as cancellation nodes may not occur.

A ladder test does not find the charge weight that shoots the tightest circular distribution, ie smallest group size.

So what does this mean for your rifle?  If you are confident that the target you posted is a fair reflection of the rifles behaviour,  then it appears that over the range of powder charges you tried, no region of significant cancellation as described above exists.

I advise you shift your focus and shoot for group size, and try to be a consistent as possible with your reloading.

            
  
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Re: First Time Ladder Testing - 260 rem
Reply #12 - Apr 4th, 2018 at 6:31am
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Nor-West wrote on Mar 26th, 2018 at 12:53am:
I like that 6 is fast and directly  (almost) above the target. I would slap a few of those through again as well.


There is no correlation between high velocity or the POI on a random target, and the inherent grouping ability.
  
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Re: First Time Ladder Testing - 260 rem
Reply #13 - Apr 4th, 2018 at 8:38pm
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puffin wrote on Apr 2nd, 2018 at 7:33pm:
Did you not get the information you were wanting on the other site?           
       


I visit both sites and I posted this around the same time - I was interested in the range of responses (and there was quite a variety of opinions). But your post on the other one, and this one was helpful - Thanks for the extra info on this time round.

I've since shot multiple groups with loads 4 and 5. Load 5 is showing the most consistent results with groups of around .75 moa if I do my part. I'll play around with seating depths - but really, this is more than good enough for me on a hunting rifle.

cheers
  
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