I have seen many different breeds and cross-breeds used in the shooting field, some of which were not of true gundog origin.
A few can do useful work, but many are limited only to certain aspects of what is expected of a gundog, such as being used solely to flush game in the beating line.
I once tried to help someone who had the idea of training a rottweiler for the gun, and it was far from successful.
The breed has no natural retrieving instinct, no athletic ability, due to its heavy-boned conformation, and a very unappealing, surly attitude to discipline.
You will not do better than to buy one of the traditional gundog breeds and – if it is a retriever you need – to go with a spaniel or labrador, though golden retrievers and flatcoats also do a good job.
It is essential to buy from good stock.
If you like rottweilers, then by all means obtain one as they make lovely house and guard dogs, but don’t expect to turn it into something for which it has not been selectively bred.