No standard distribution of bullet dispersion?? 5 shot groups useless?
- Thread starter Utectok
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Utectok
Well-Known Member
I guess he’s saying during load development or tuning a rifle and ammunition it’s not possible to detect any significant difference with the standard procedure of 5 shot groups. You may as well pick a MV you like and a powder charge you fancy to produce it and load to Sammi length? All the rest is just wasting ammo
Unless you use a machine rest a lot of the variables are how you how the rifle which varies subtly each time you get into position, there are over 600 muscles in our body to position exactly the same.
I used to shoot an Anschutz Super Match in 22lr, moving my thumb position produced a repeatable and consistent change of impact of 1/4" at 100 yards.
I used to shoot an Anschutz Super Match in 22lr, moving my thumb position produced a repeatable and consistent change of impact of 1/4" at 100 yards.
Isn't that a 10-shot group?
Foxyboy43
Well-Known Member
It is more like a demonstration of consistency, but yes. A 10 shot group. ~Muir
You mean like the 8 shot group I shot at 300yds that could be covered with a half dollar coin...with a sling...iron sights...and a rack grade M-16A2 and green ammo can ball ammo?
Position does matter (proper form), but if shots are stringing because you moved just your thumb...sumtin' else be screwed...
ETA: Oh, and it was a 10 shot group. the other two shots were 1" to the right...and both touching. But that was after having to change magazines (2 shots from one mag, 8 shots from the other). i.e. break position
Those two statements seem at odds with each other:Position does matter (proper form), but if shots are stringing because you moved just your thumb...sumtin' else be screwed...
ETA: Oh, and it was a 10 shot group. the other two shots were 1" to the right...and both touching. But that was after having to change magazines (2 shots from one mag, 8 shots from the other). i.e. break position
He changes his hold/position - his POI moves, so something else must be wrong. However, if you change your hold/position - your POI moves, and that's fine?
Moving a thumb is a bit different then unshouldering the rifle and sling, dropping a mag, reaching around to grab another mag, then insert it, get back into position and on target to shoot. At 300yds.
IDK, but that seems like a big difference to me....what do you think?
Sounds plausible to me. The shift is about the same as your 1" at 300yds.
We know changing hold can change POI, and in this chap's case he at least seems to have analysed this hold/position and identified the cause of the shift quite specifically - which IMO is the correct approach if that degree of precision is called for.
ChesterP
Well-Known Member
A lot of expert ballisticians might disagree with those findings, as statistically the law of diminishing returns kicks in at 10 shot groups for precision loading (more than you need to consider for deer stalking) with an economical optimum statistically as 7 and no less than 5. I agree with Muir, as I find shooting at 7 or 10 for LR precision loads, single dots spaced out at several inches apart as I can focus precisely on the dot each time, then invariably miss it anyway. It's easier noting which you may have pulled or been less than consistent with on trigger technique that way.
I haven't bothered with ladder development except to pressure test single shot ladders from 3/4 max recommended upwards and have been exclusively using and developing with calibrated GRT models for well over a year if not longer. It's saved a small fortune in ammo wastage and has proved ultra reliable for me anyway once calibrated. It does require a modicum of detailed internal ballistic know how to get the most from it but that's where it's at its most useful, used in conjunction with custom OBT profiles.
My steps are:
Ever since getting involved in the detail behind the model with some far more expert than I in the internal ballistics field, it's also proved useful for precision shooters and perhaps may do (discussions ongoing) for a certain team. It betters their results using QL due to the additional parameters and complexity of GRT.
I haven't bothered with ladder development except to pressure test single shot ladders from 3/4 max recommended upwards and have been exclusively using and developing with calibrated GRT models for well over a year if not longer. It's saved a small fortune in ammo wastage and has proved ultra reliable for me anyway once calibrated. It does require a modicum of detailed internal ballistic know how to get the most from it but that's where it's at its most useful, used in conjunction with custom OBT profiles.
My steps are:
- build the model for cal/barrel/twist/case capacity/COL/bullet/Powder
- play with powder choices to get to 97 or 98% burn rate at muzzle and above 95% load ratio for uniformity of ignition
- run model and pick a max load of "PMax-15%" then shoot 5 at that to get average MV
- calibrate model for OPT using obt function
- run OBT and take closest matched loads for BLT to OBT which I want to see within max 0.05msecs
- pic the nodes giving this with pressure insensitive region spread of 0.4gr. Note: these can be well below or well above PMax -15 and I ALWAYS reject those above.
- pick middle of that and load 5 more for each of those three nodes identified
- shoot 15 rounds plus start with ladder from just below to just above in 0.2grn intervals for pressure safety test
Ever since getting involved in the detail behind the model with some far more expert than I in the internal ballistics field, it's also proved useful for precision shooters and perhaps may do (discussions ongoing) for a certain team. It betters their results using QL due to the additional parameters and complexity of GRT.
It struck me that while the geezer is correct statistically it is leading to some incorrect conclusions.
While it may be statistically invalid to claim that the load produces say a 0.5moa group it is not necessarily wrong either, there just isn't enough evidence to support that to a high degree of certainty. Nor is it necessarily wrong to say that the 0.5moa load does produce a tighter group than the load that produced say 0.75moa. So our processes (probably) do provide usable data to select better loads provided we are not looking at very small differences when much larger number of shots will be required.
If you have one load that shoots one 1/2" group at 100 then the chances are it will be a better load than the one that produced one 1" group. Firing another couple of groups will let you know whether it was a fluke or not, and whether that conclusion is really about right.
Good enough for us. We don't need to be statistically valid unless we want to be a top notch target shooter, and probably not even then.
While it may be statistically invalid to claim that the load produces say a 0.5moa group it is not necessarily wrong either, there just isn't enough evidence to support that to a high degree of certainty. Nor is it necessarily wrong to say that the 0.5moa load does produce a tighter group than the load that produced say 0.75moa. So our processes (probably) do provide usable data to select better loads provided we are not looking at very small differences when much larger number of shots will be required.
If you have one load that shoots one 1/2" group at 100 then the chances are it will be a better load than the one that produced one 1" group. Firing another couple of groups will let you know whether it was a fluke or not, and whether that conclusion is really about right.
Good enough for us. We don't need to be statistically valid unless we want to be a top notch target shooter, and probably not even then.
Utectok
Well-Known Member
I think the point he is making is that if you have a load that shoots 1/2 groups at 100m and you have a load that shoots 1” groups you simply have no idea which is better. The same load may shoot 1.5” groups or 1/2 groups
Utectok
Well-Known Member
Interesting the non standard distribution though!Do I need to go crank up the simulator again?
billgatese30
Well-Known Member
I'm not sure I agree with his logic. Why add the second SD/curve, what is that supposed to represent? Lots of input variables create one factor which is shot placement (i.e. the distance from the aim point regardless of angle). The way he adds the second SD and thus the 2nd distribution was like having two rifles firing simultaneously at the same POI. The way he sets two curves which stay on each side of the POI makes zero sense and generally speaking that is not how bimodal distributions generate over time.
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