Pat,
you have many options, and both of us not being US citizens and currently living outside the US makes things even easier.
Strelok
(a) For iPhone, just don't delete it from your old phone, but transfer it to your new iPhone.
Instructions:
Because this is a stolen and repackaged code of my program! Don't buy from pirates! What are the odds you are going to get your app back up?
www.snipershide.com
o
(b) For Android you have 2 work-arounds with 2 non-Google app stores:
Instructions here:
● (Samsung) Galaxy Store —
only for Samsung cell phones
Get the latest games, apps, tools, and more and enjoy exclusive offers for Galaxy users. Visit the Samsung Galaxy Store now!
galaxystore.samsung.com
● Huawei AppGallery
If your Android is not a Huawei, then first install the Huawei AppGallery.
Then, in the Huawei AppGallery, install Strelok Pro.
(c) I'll send you a PM with a 3rd solution.
GPC Ballistics
By GPConway (George P. Conway)
In all platforms: Android, iPhone; Windows, MacOS, Linux
Many, many functions, specifically made for airgunning. Awesome!
Link:
A few ballistics applications for Windows, macOS and Linux written in the PureBasic programming language.
gpc.fotosoft.co.uk

ChairGun Pro
The original app, from Hawke scopes.
Though discontinued, it still works on cellphones, and on windows computers. Sometimes you need to get an emulation program for an older operating system.
The windows version is still very powerful, many functions!
Hawke is a global leader in high-quality, great-value sporting optics, including rifle scopes, binoculars, spotting scopes, and more.
www.hawkeoptics.com
Updated for computers, here: Windows, MacOS, y Linux:
chairgun-use.github.io
Cheers,
Matthias