Thread: Field Ranges in NZ - Reduced Danger Area Example

Originally Posted by Tentman

Thanks for taking the trouble to share and explain this. Couple of questions if you can . . . .

Why are calibre limits being used as opposed to energy limits?

In the tier 3 scenario is the slope behind the target (effectively the bullet stop) the key factor?

Thanks

Thanks @Tentman, some good questions - I mentioned I would leave a bunch of stuff out.

Your first question - energy doesn't necessarily translate well to the "how far will a projectile travel" question. It does come into the ricochet ballistics a bit as it is a consideration of the residual kinetic energy of the ricocheted projectile. Energy is also really handy to know at the impact point when looking at protective structures or target suitability (e.g. determining a suitable steel target thickness). Energy is also a variable that not a lot of "normal" shooters are familiar with - calibers / cartridges are. The caliber limitation mostly works as a simplistic measure that is fairly easy for most people to understand and it is fairly easy to "police" onsite (no chronograph required) - there are some obvious exceptions around black powder rifles (which are excluded entirely at the moment) and the big caliber air rifles. The "Up to 8mm" designation also falls over with some of the magnum calibers (e.g. 28Nosler, 300PRC and 300Norma).

Our system is broken down into:
22LR - covers most rimfire cartridges.
308Win - covers all “standard” non-magnum cartridges up to 8mm in caliber including but not limited to 223Rem, 243Win, 270Win, 284Win, 30-06 Springfield, etc. Also includes the smaller magnums including 6.5PRC, 264WinMag, 7mmRemMag, 300WinMag, etc.
338Lapua - covers all magnum cartridges including but not limited to 28Nosler, 300PRC, 300NormaMag, 338Edge, etc.
50BMG - covers all large magnum cartridges including but not limited to 375CheyTac, 416Barret, etc.

Your second question - the slope angle is one of a bunch of variables in the Tier 3 system (I find it easier to consider "impact angle"). But on top of that, ground material, land usage, target distance / cartridge template applied, governing ricochet angle, line of fire angle, cone of fire size, etc. all come into the Tier 3 system.
In the example above, the Tier 3 range danger area is made up of both targets where ricochet is credible and targets where ricochet is not credible. Where ricochet is credible, the range danger area for some targets is limited by the line of fire angle, and for others the height of the hill behind catches the ricochet. Then lastly, just because ricochet is not credible at a particular target location that doesn't mean there is not a range danger area - I would be "uncomfortable" enough to stop shooting if someone walked over the hill the target is on even though they were technically outside of the cone of fire...