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Use the centre of each circle to read off the horizontal and vertical axis. Circle sizes are proportional to the rifle’s recoil velocity.

What are “Ballistic Coefficient” and “Sectional Density”?

Check out this wikipedia page for Ballistic Coefficient and this wikipedia page for Sectional Density.

What is “G1 Model”?

Check out this wikipedia page. About a third of the way down it describes a number of drag curve models, including G1 or Ingalls drag curve model.

OK, so why did you choose the G1 model and not one of the other models?
All projectile manufacturers quote ballistic coefficients using the G1 model for consistent comparison between products.  Using a manufacturer’s published ballistic coefficient with a model other than G1 is inconsistent and will produce mis-leading results.

Why did you choose a six inch Maximum Point Blank Range?

The default data table is calculated using a six inch Maximum Point Blank Range (3 inch deviation above and below the Line of Sight). I realise that some sources recommend a larger Line of Sight deviation to calculate Maximum Point Blank Range. However, my calculations suggest that a surprising number of cartridges enter the transonic zone near these greater Maximum Point Blank Ranges. The transonic performance of projectiles is notoriously fickle and so I have used 3 inch Line of Sight deviation (76mm) to avoid transonic instability for all of the listed cartridges. A data table using a two inch MPBR is available as an in-App purchase.

Why are your estimated MPBR different from those given elsewhere for the same cartridges?

External Ballistics is a complicated field. MPBR will vary depending upon temperature and relative humidity. Nevertheless, CartridgeChooser provides reliable comparisons of the relative performance of cartridges. The idea is to include a cartridge or two with which you are familiar in the Summary view. Any errors in calculation will be consistent between all cartridges so their relative performance will provide a reliable comparison.

6in-15Aprv1 MPBR

Circle sizes indicating relative recoil between some Weatherby Cartridges

I have checked numerous source’s figures for MPBR, Energy, recoil, etc. CartridgeChooser varies from these by at most 1-3% and often it could be because the base conditions (temperature, humidity, etc) are not quoted and may differ. I find the tables provided by these sites are hard to properly visualise. The advantage of using CartridgeChooser over tables of figures is how the visual comparison emphasises the relative performance over the absolute numbers.

Remember, a cartridge’s suitability for particular game depends on projectile construction and placement as much as the energy delivered. Nevertheless the relative performance of similarly constructed projectiles can be compared using sectional density multiplied by energy at the Maximum Point Blank Range (not at muzzle as many sources do). Users should always rely on actual performance and the advice of experienced shooters over any theoretical model.

What do the circle sizes represent on the MPBR and SD-BC views?

The size of these circles is proportional to recoil.

How did you calculate Recoil?

Recoil velocity = projectile mass * muzzle velocity / rifle mass. Relative Recoil = [Recoil /Max] and Max is maximum recoil in the Summary rows. The Summary view allows the User to select a cartridge to replace Max in the above calculation of relative recoil. In this way the recoil of each row can be relative to the selected cartridge. I have used a number of common rifle weights across different calibre’s to estimate recoil. For example; small .22 calibre’s use a rifle weight of 7lbs, short actions 8lbs, standard actions 8.5lbs and magnum actions 9lbs. In every case 1lb is added to account for a scope and mounts.  Whether you consider recoil to be moderate or heavy is a matter of personal build and experience. However, if you select a cartridge load that you are familiar with as the recoil baseline, then you can reliably compare recoil between cartridges by observing the relative diameters of the bubbles.

What is the “Angle above LOS” column for?

By comparing the angle above line of sight between two loads you can estimate the hold-over necessary if you zero for one load and then use another. This is of limited practical use but I thought some might find it interesting.

Come up at 100 Yds?

‘Come up at 100′ is 100 yards (100 meters in the metric view) should help you zero close to your Maximum Point Blank Range without access to a large sighting-in range. Aim centre of target and if your group is centred this distance above your point of aim then you should be zeroed for MPBR.

The ‘Come Up’ for my cartridge is negative. What’s going on?

If the come up for a cartridge is negative it means one of two things. Either the projectile is a high velocity projectile and it is still rising towards zero, or it is a low velocity projectile and at 100 yds (m) it has already fallen past zero. To tell which, have a look at the zero range. If it is greater than 100 yds (m) then the projectile is on its way up. If its less than 100 yds (m) the projectile has fallen past zero. This second case usually occurs in the 2 inch (50mm) MPBR because these cartridges do not have a sufficiently flat trajectory and are not a good choices to use with the 2 inch MPBR.

How do I switch to a metric view?

A user selectable option on the Control view determines whether Imperial or Metric is displayed. When the user changes between imperial and metric, the summary and bubble views change, but the selected cartridges do not require re-selection by the user.Cartridge Choser Banner AD 3

When I delete the reference cartridge from Summary view, the relative recoil does not re-calculate.

Pressing ‘Reset’ re calculates the relative recoils.

MPBR and SD-BC views are difficult to manually return to the default view after zooming.

If you leave and return to the view it is re-set.

How do the filters work?

There are 485 cartridges in the Library view and I plan to add more. Having no filters selected displays all 485 in a long list. To help find the cartridge you want, you can touch the Library column headers which will sort by that column. Better still, you can select a filter to narrow down what is displayed in the Library. Don’t worry, it doesn’t affect any earlier selections in the Summary view, the filters just help narrow down the displayed Library.  The Game Class filters have an ‘OR’ rule between them as do the Recoil filters. Whereas between any combination of Game Class and Recoil filter there is an ‘AND’ rule. Selecting a filter means ‘show me only those cartridges which meet the selected criteria’. i.e; show Class-2 only, show cartridges which are either Class-1 OR Class-2, show cartridges which are both Class-3 AND low recoil (there won’t be many of these). NOTE: These filters are available through an in-App purchase.

 

What parameters did you use to calculate MBPR?CartridgeChooserWebPageIcon

Apart from the parameters visible in the Library view, the following were used in the simulation:

Atmospheric Pressure: 1013mBar (101.325 KPa)

Temperature: 77F (25C)

Relative Humidity: 78%

Scope Height above barrel: 2 inches (50mm)

Time Increments: 1millisecond

Angle Increments: 1/100 MOA

If you think I should use different parameters, go to the Community page and share your view…

What is Game Class?

Class – 1 class game includes small game, weighing less than 50 lbs (23 kg). Examples include; rabbits, foxes, woodchucks and coyotes.

Class – 2 class game are light framed animals with thin skin, light muscles and bones. Examples include; goat, small deer, antelope, sheep, and black bear. They range from about 50 lbs (23 kg) to 300 lbs (136 kg).

Class – 3 class game are large framed, heavy animals with thick skin, tough muscle tissue and large bones. They range from 300 lbs (136 kg) to over 1000 lbs (454 kg). Examples include; elk, moose, zebra, kudu, eland, and brown bear.

Class – 4 class game are the extra large, very thick-skinned animals. They are primarily African species such as cape buffalo, hippo, rhino and elephant, but also include Asian and Australian wild water buffalo and American bison. These animals range from about 1000 lbs (454 kg) for Cape buffalo and up to 12,000 lbs (5400 kg) for African elephant.

As stated a couple of times, CartridgeChooser is a useful tool for comparing the relative performance of various cartridges. If you are familiar with a particular cartridge and load, then including it in your summary view provides a reference point against which you can compare other cartridges. I usually choose .308 in a variety of loads, or for smaller calibre’s I select .222, as I have used these in a number of situations over many years and am familiar with their performance and recoil.

How did you calculate the ‘Game Class’ scale?

The Game Class scale is just energy at MPBR multiplied by projectile Sectional Density. Other game class scales exist, but they are usually proprietary and include empirical parameters to account for projectile construction. Clearly projectile construction is a factor and manufacture’s recommendations should always be considered before selecting an appropriate projectile. However, as long as you compare like-to-like and include a couple of reference cartridges with which you are familiar, the relative performance between cartridges can be visually compared using CatridgeChooser.

How did you decide where the boundary between each Game Class should lie?

I researched a variety of sources and observed where the cartridges they recommend lie on the Game Class scale. These Game Class boundaries are just a guide, projectile construction and bullet placement are significant factors which must also be considered. If you still think I’ve chosen these boundaries poorly, please tell me and say where, on this scale, you think they ought to lie.

Where are the PDFs I generated?

They are in your iTunes under Apps >>> CartridgeChooser.

Why only iPad?

There are so many Android devices… I’m not sure which is best for an App of this sort. Do you want an Android version? Which devices do you prefer? Tell me at Community.

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