You mentioned wanting some red in the final outcome.
If you rely on only Aqua Fortis you are at the mercy of the wood and the solution.
Each piece of wood will react differently and the only way to know what you will get is to test it on a piece of wood from the stock you have.
Another seemingly identical piece of wood cut from a different place on the same tree will react differently.
You might get some red and you might not.
If you are serious about wanting to have some red tone, IMO, the best way is to have some alcohol or water base mahogany stain handy.
After doing your Aqua Fortis thing, if the results are not giving you the red tone you want, thin the mahogany stain down using either water or alcohol by a factor of at least 5 parts thinner to 1 part of stain. A 10:1 ratio might even be better.
The idea here is to sneak up on just the right amount of red tint.
Being greatly thinned, each coat will add just a little red but because the stain is alcohol or water base you can repeatedly re-stain the wood to make it darker and add a little more red.
Do remember, the actual color and darkness will only show while the stain is wet. When it dries, it will look much lighter.
I should add, even with alcohol based stains, the final results will depend greatly on the individual piece of wood you are working with.
The rifles in the following photo were all stained only with various color alcohol based stains.
Some just with walnut. Some with maple and some with a combination of walnut, maple and mahogany.
Aqua Fortis was not used on any of them.
maplestripesweb by
James, on Flickr