In case anyone is interested, the MLAGB are doing postal competitions for single shot, revolver and modern muzzleloaders. Entry forms are here:

https://www.mlagb.com/Client/Documen...m_2021-22.docx

and the rules are such that anyone can join in, scale targets are permitted so even those with 20yd ranges can take part. They are even allowing two handed shooting if there’s a medical need.