I vote aqua fortis (nitric acid) as well. Nothing brings out the curl and grain like it and it really isn't hard to use. Just practice on a scrap or two to see what it does and you should be fine.
I've used it on only 2 stocks, but dozens of smaller maple items like knife handles, bullet blocks, powder horn plugs etc. and I've tested different homemade nitric based stains on dozens more scrap pieces of maple and I've never seen one turn any shade of green. Not saying that it's never happened but I sure was surprised to read in forums like this that "my friend's gun turned green!" and so on. I wonder how prevalent it actually is.
I was taught to apply the acid, heat it, neutralize it, then apply chromium trioxide and let it dry. Perhaps this step is what prevents some maple from turning green, but I've skipped the chromium with good results too.
To keep an acid stained gun from getting darker in the future you need to neutralize the acid with a baking soda or lye wash. The gun will get darker EVENTUALLY, but it'll take a long time.
I stained a pipe box with an alcohol based stain a few years ago, and contrary to the rumors, it raised the grain just as much as the acid, and I've noticed the color fading too. It just didn't look as good as the acid either. Others may have had better luck with it.