Stinky Coyote
WKR
I didn’t want to hijack the .223 thread any further with where I’d like to go with the key minds on modern terminal ballistics here at Rokslide.
Pretty sure we can all agree on a couple things to kick this party off.
I’ve had some thoughts around this for awhile and started to put things on paper early in 2020. Trying to find ways to level this playing field, are there measures we are missing and could be working on to help explain things more objectively? I’ll give an example of where I’ve started to go here…
SDRR (sectional density reduction rate) is a term I came up with as a possible new measure to help explain/compare bullets to one another. In conjuction I came up with ERR (energy reduction rate) to go with that as another possible measure we could work with to help explain better the internal work. I’ll give an example using Form’s 77 gr tmk recovered from the elk and can give one of mine as well. Now I’m not trying to sell this as the way to go, I’m still trying to let my head wrap around ideas here as we go and this looks like a great forum of minds that could add to this.
So Forms 77 tmk example, initial data points to work with. Starting SD .219, Impact Velocity 1900 fps, impact energy 617 ft/lbs, distance traveled 17”, ending bullet weight 30 grains, ending SD (lets use .5” diam x 30 grains) so final SD .017. With a 2.?x expansion ratio added to the mix to show expected expansion ratios. 1.5x up to 3x sort of thing.
So in my mind there’s measurable information there we aren’t talking about yet. There are delta’s between the start of that 17” of travel and finish…those numbers aren’t currently being discussed at this point, let alone applied. There’s no current system of factory standards to measure these things so we are going to be using inconsistent mediums of ‘game’ at this point to help illustrate future potentials.
Forms recovered example shows a delta of .202 SD split up over 17” or .01188 SD per Inch, or one might be able to then convert that to an easier number to compare such as percentage of reduction per inch? In this case maybe it’s 0.1188/.202 for 5.9% SDRR (per inch) and then to help explain some of the terms like temp/permanent stretch cavities apply also the energy side of it in the same way, we started with 617 ft/lbs and dumped it all over 17” for 36.3 ft/lbs per inch or an equal 5.9% ERR.
So my vision for how to develop this further is to of course find a medium that would allow us to compare bullets equally in (gel? Not sure) but if one could do this with so much of the subjective experience we already have on known bullets from old and new…it may prove possible to compare and better predict terminal performance going forward.
Currently SD is our only indicator, and to some extent BC to help define aero/shape which forsure plays apart and I’ve largely ignored to this point so I admit if this carries on there will be more factors to include in the equation as BC is an aero measurement we use ‘in-flight’ but surely matters for the terminal swim also. I just want to start talking about how to get better measures or data points to discuss post impact. Currently we have to combine SD, with construction type(some ‘shape) to ‘imagine’ how things will play out.
I’ll leave the forum open at this point for further comments or ideas, hopefully now is the time to push this part of the equations a little further? We are definitely doing it afield and figuring lots out as we go, I’m in there hammering with a Grendel 16” and 123gr eld-m’s and it’s doing everything I can see/feel in my mind…and the .223 thread seems to be a perfect example of possibly the lower limits etc.
For a long time I thought ft/lbs was a useless measure, and maybe that will still prove true?, but after working some of this out in my mind I feel like maybe there is a way to incorporate ‘energy’ into the equations to help explain that internal work. My main formula is still primarily ‘for game intended’ matching SD, with construction, and impact velocity…get that right and there’s magic. There is a magic formula but we don’t have the best data or measures to explain that yet. Maybe better measures are thought of during this discussion?
Pretty sure we can all agree on a couple things to kick this party off.
- The in-flight ballistics we’ve got down pat, all the right numbers, measures and thorough understanding of it all. We’re able to maximize the peak potential of our rifles and gear now to levels never even talked about 15 years ago for most.
- The terminal ballistics we don’t have quite to the same level. This is the topic we still argue the most about as a whole, still have too many gaps, lack of potential measures, and it’s a subjective mess for most of the discussions…IE; 67 pages on the .223 thread.
I’ve had some thoughts around this for awhile and started to put things on paper early in 2020. Trying to find ways to level this playing field, are there measures we are missing and could be working on to help explain things more objectively? I’ll give an example of where I’ve started to go here…
SDRR (sectional density reduction rate) is a term I came up with as a possible new measure to help explain/compare bullets to one another. In conjuction I came up with ERR (energy reduction rate) to go with that as another possible measure we could work with to help explain better the internal work. I’ll give an example using Form’s 77 gr tmk recovered from the elk and can give one of mine as well. Now I’m not trying to sell this as the way to go, I’m still trying to let my head wrap around ideas here as we go and this looks like a great forum of minds that could add to this.
So Forms 77 tmk example, initial data points to work with. Starting SD .219, Impact Velocity 1900 fps, impact energy 617 ft/lbs, distance traveled 17”, ending bullet weight 30 grains, ending SD (lets use .5” diam x 30 grains) so final SD .017. With a 2.?x expansion ratio added to the mix to show expected expansion ratios. 1.5x up to 3x sort of thing.
So in my mind there’s measurable information there we aren’t talking about yet. There are delta’s between the start of that 17” of travel and finish…those numbers aren’t currently being discussed at this point, let alone applied. There’s no current system of factory standards to measure these things so we are going to be using inconsistent mediums of ‘game’ at this point to help illustrate future potentials.
Forms recovered example shows a delta of .202 SD split up over 17” or .01188 SD per Inch, or one might be able to then convert that to an easier number to compare such as percentage of reduction per inch? In this case maybe it’s 0.1188/.202 for 5.9% SDRR (per inch) and then to help explain some of the terms like temp/permanent stretch cavities apply also the energy side of it in the same way, we started with 617 ft/lbs and dumped it all over 17” for 36.3 ft/lbs per inch or an equal 5.9% ERR.
So my vision for how to develop this further is to of course find a medium that would allow us to compare bullets equally in (gel? Not sure) but if one could do this with so much of the subjective experience we already have on known bullets from old and new…it may prove possible to compare and better predict terminal performance going forward.
Currently SD is our only indicator, and to some extent BC to help define aero/shape which forsure plays apart and I’ve largely ignored to this point so I admit if this carries on there will be more factors to include in the equation as BC is an aero measurement we use ‘in-flight’ but surely matters for the terminal swim also. I just want to start talking about how to get better measures or data points to discuss post impact. Currently we have to combine SD, with construction type(some ‘shape) to ‘imagine’ how things will play out.
I’ll leave the forum open at this point for further comments or ideas, hopefully now is the time to push this part of the equations a little further? We are definitely doing it afield and figuring lots out as we go, I’m in there hammering with a Grendel 16” and 123gr eld-m’s and it’s doing everything I can see/feel in my mind…and the .223 thread seems to be a perfect example of possibly the lower limits etc.
For a long time I thought ft/lbs was a useless measure, and maybe that will still prove true?, but after working some of this out in my mind I feel like maybe there is a way to incorporate ‘energy’ into the equations to help explain that internal work. My main formula is still primarily ‘for game intended’ matching SD, with construction, and impact velocity…get that right and there’s magic. There is a magic formula but we don’t have the best data or measures to explain that yet. Maybe better measures are thought of during this discussion?
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