If you mean a 577/450 in a MkIV and it is a Pattern A or B and you are using Lee dies, you better Anneal after every firing. C Pattern MKIV you might get away with every other firing.

I strongly recommend you read and heed the guidance Dr. Howell's article on annealing, June, 96 Cases

It is very easy to burn one of these cases trying to eyeball anneal these large cases. At $4 to $5 a case when a case fails from being burned, you will weep!

There is no such thing as a MK 4 Martini Henry.