Bullet Stabilization Pt 2 : Ladder test and Chronograph

[ecomeat]

Took the opportunity Friday day to do a Ladder Test at 300 yds as suggested by Allan, with my 6 x 47 Lapua, putting all shots through a Master Beta chronograph.
My standard load is 38 gn 2209, ICI BR4 Primers and now 105gn Berger Hybrids seated .001 off the lands.
Barrel is a 30" S.S. Krieger with 1 in 8 twist ,
I had been using the same load with Berger 105 gn VLD's seated just touching the lands, and it had chrony'd at the 2975 i mentioned in initial post. A big shock with the new Berger 105gn Hybrid results yesterday ......and a strong lesson learnt for a newbie like me, that wont be forgotten in a hurry ! All shots much faster than expected.

No adjustments made for windage, as only interested in vertical spread.
Sighter/Fouler 1. and Sighter/Fouler 2. were both 38.0 gn loads, as was the 38.0 gn in middle of ladder and all 3 were loaded two weeks ago.
I use a RCBS Chargemaster and then check every load on RCBS beam scales.
Friday, loading 37.0 to 37.9 then 38.1 to 39.0, plus 39.2, 39.4, 39.6, I used the RCBS Chargemaster to throw 37 gn, then trickled into pan of RCBS beam scales to get each load.
Temp was approx 30 deg.
Fouler 1 3042 fps and high. Loaded 2 weeks ago
Fouler 2 3115 fps and high. Loaded 2 weeks ago
Shot 1 (37.0 gn) 3052 fps
Shot 2 (37.1 gn) 3066 fps
Shot 3 (37.2 gn) 3070 fps
Shot 4 (37.3 gn) 3101 fps
Shot 5 (37.4 gn) 3093 fps
Shot 6 (37.5 gn) 3119 fps
Shot 7 (37.6 gn) 3105 fps
Shot 8 (37.7 gn) 3126 fps
Shot 9 (37.8 gn) 3121 fps
Shot 10(37.9 gn) 3131 fps
Shot 11 (38.0 gn) 3099 fps . Loaded 2 weeks ago.
All shots 1-11 except one were within top half of 6 Ring for Vertical.(within 1.25" or 0.41 moa)




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I then let the barrel cool for 5 mins, before resuming.
Shot 12 (38.1 gn) 3089 fps
Shot 13 (38.2 gn) 3135 fps
Shot 14 (38.3 gn) 3119 fps
Shot 15 (38.4 gn) 3137 fps
Shot 16 (38.5 gn) 3133 fps
Shot 17 (38.6 gn) 3144 fps
Shot 18 (38.7 gn) 3142 fps
Shot 19 (38.8 gn) 3149 fps
Shot 20 (38.9 gn) 3168 fps
Shot 21 (39.0 gn) 3175 fps
Shot 22 (39.2 gn) 3184 fps
Shot 23 (39.4 gn) 3200 fps
Shot 24 (39.6 gn) 3213 fps
All 13 shots in 2nd string also within top half of 6 ring, so within 1.25" or just over 0.4moa
Easy bolt lift (BAT Model M L/H action)
Primers look fine to me. No cratering, not really flattened except the last 3 shots getting up to the 3200 fps mark.
Shot order in photo below is bottom to top, starting with 2 x foulers on left side, Shot 11 of 38 gn alone in middle and finishing with 3 shots on far right around 3200 fps
I would greatly appreciate your experienced comments on primer appearance. Am I missing something, or are they OK ?



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Is it innacurate beam scales that causes the "out of order" velocities ? Or can that sort of thing just happen for whatever reason ?

I am an old cow cocky who likes shooting wild dogs, and not an old benchrester, so the .4moa is probably as much as I am capable of at this stage. I have only been shooting F Class for 12 months and its been a steep learning curve.
For 50 odd years , if you have a miss in the bush, its rarely possible to know for certain how far you missed by......its just a "miss", or "I nearly hit it".....so to have someone drop the target and mark each shot conclusively is a whole new ball game.
Ecomeat

[bruce moulds]

eco,
a ladder test gets very busy on paper using 0.1 gn increments. 0.2 in the 6.5x47 is better, and 0.3 in a 284 scase capapacity is probably good.
your velocity readings are quite normal to experience.
another thing with ladder tests is that nodes become more apparrent at 500m, because the gaps between the holes are wider.
your test brings home the inherint accuracy of that cartridge.
keep safe,
bruce.

[AlanF]

eco,
a ladder test gets very busy on paper using 0.1 gn increments. 0.2 in the 6.5x47 is better, and 0.3 in a 284 scase capapacity is probably good.
your velocity readings are quite normal to experience.
another thing with ladder tests is that nodes become more apparrent at 500m, because the gaps between the holes are wider.
your test brings home the inherint accuracy of that cartridge.
keep safe,
bruce.

Bruce,

If there is a trend in the ladder with say 0.3gn increments, but not with 0.1gn, then you should believe the 0.1gn data! In my opinion, more shots = more information (same as with groups - 5 shot groups are only good for eliminating bad loads, not for selecting good ones).

And I agree with you that 500 is a better range for ladder testing, but was expecting more elevation variation at 300, given eco's original description of the problem.

Alan

[Aubrey]

Here's the data in a spreadsheet - hard to see if there are any nodes - maybe someone can see it better than I can.



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[bruce moulds]

alan,
we'll have to beg to differ on that one.
i do feel that a good node needs to be + or - 0.3 gn in a 284 (read 30/06) case capacity. using larger steps minimizes the temptation to think you have GOOD node of + or - 0.1.
once you find a + or - 0.3 node, you can go to 10 shot groups within that node.
i liken the larger spread of charges to measuring extreme spread. you only use 2 shots to do it, no matter how many in the sample.
eco's test adds to my theory that the 6.5x47 could be the ultimate team shooting cartridge.
the sheer accuracy it has would make coaching 5 shooters in a row quite a breeze. add to this the slight gain in wind deflection available to a low vert grouping gun and you could have a daunting combo, particularly in north qld.
keep safe,
bruce.

[AlanF]

Eco,

It looks like what you've graphed is the velocities (vs powder charge)?

Its important to look at impact height. Normally I draw a horizontal line on the target beneath all the shots and measure the height of each shot above the line. To do this each bullet hole needs to be numbered sequentially (i.e. you need a marker). You can then graph charge vs height and velocity vs height. The latter is in my opinion the best indicator of the effect of barrel harmonics.

Bruce,

I'd like to encourage you to become chief strategist for the SARA F-Class team. Making a statement about the merits of the 6.5x47 based on the performance of a 6x47 is just the sort of advice we'd like them to have.

Alan

[bruce moulds]

alan,
i could say"woops how embarrassing", or this could be a cunning south aussie plan for mackay, playing with the minds of opposition teams in advance.
only time will tell.
bruce in the dementia unit, or sa using 6.5x47 lap?
keep safe,
bruce.

[ecomeat]

I will do the ladder test again, now that I have a lot better understanding of what can be achieved, and how it should be done. I will get each shot marked, and quickly photographed, so that I can do the measured vertical spread that Alan has referred to.
If I did 36.6 gn to 38.8 gn, in 0.2 gn increments, 12 shots in all, would that be enough ?
If i do it at 500 yards first, and then do it all again at 300 yards, that should answer a lot of questions about my 300 yard issues with poor results, for a total of 24 shots ??

Having done the 0.1 gn increments over the chronograph , can i leave the chrony out of it this time around to speed things up, and still get meaningful data re "nodes" ??
Regards
Ecomeat

[ecomeat]

I just reread Alans last post re Velocity Vs Vertical Height, and accept that it is important, so will add the chronograph at both 500 and 300 yds

[Norm]

I would exclude the data from the two week old loaded rounds.
It is my understanding that neck tension can change with the amount of time that a round has been loaded.
ie the neck tension on the two week old rounds could be higher than that for the freshly loaded rounds resulting in a velocity that is inconsistent with what you may have obtained had all the rounds been loaded at the same time.
This could be part of the reason for the dip in your graph at the 38gn range.

[Barry Davies]

One shot only is not indicitive simply because 5 or ten shots of the same load will give a spread in speeds which could be up to 35 f/s more or less.
The question is of course, where in the ladder is the low speed shot going to hit and where is the high speed shot going to hit? and the speeds of that load will overlap the speeds of loads below it and above it.
So one shot means nothing.
If all shots at a particular load gave the same speed there would be some meaning to it.
Barry

[DannyS]

I agree with Barry. Thevelocity of one shot means nothing. Its the spread of velocity of a group of shots thats important.

[bruce moulds]

aubrey's graph COULD (not necessarily does) suggest that after 38.5 gn,s.d. reduces for whatever reason.
what case life is in this zone would have to be determined.
keep safe,
bruce.