I have a custom stock that was fitted to a Kimber model 82 22LR. it was fitted to the gun, whiskered properly, then stained with aqua fortis and heated with a heat gun. Unlike most muzzleloader stocks finished this way, the soft grain didn't take the stain well and left it splotchy. The stock was sanded and the stain repeated with no improvement. I can see the fiddleback in the wood, but the stain doesn't bring it out. On the two guns I did this way, I heated the stain over a gas stove burner. Any suggestions for a proper staining? I thought about leather dye, but I've never tried it. The customer who provided the wood cancelled this stock and had a walnut stock fitted. If I can get it stained properly, I'll find a rifle to fit it. Photos below.

https://postimg.cc/gallery/XFGRzgk

There isn't a whole lot of really distinct curl in that stock. Seems more of a mottled type figure. I'd use an alcohol base NGR stain and move on. You can get them from about any muzzleloading supply house.

Not sure why the muzzy was mentioned.
I'd clean as much of the dark stain off as you can with any of the three acetone, alcohol or mineral spirits (paint thinner). May need to use a filler/sealer of some sort. See what Minwax Gunstock stain does. It has a red-ish tone.
I've had wood like that that had drastic hardness differences in between grain flows and was blotchy as hell with a walnut stain, usually the Asian woods. I ended up putting a distressed finish on it to make it look old.
Try using a thinned water-based paint to tone the wood inside the barrel channel. Then try a small spot over that with the stain to see if there is any improvement.

mr. vol717: Its quite well known to hi-end furniture builders that using dye to bring out the figure ( especially curly) is very effective with maple. I have used dye on nice curly maple wood with very good results, so much so that I wouldn't consider finishing figured maple with conventional stain. Something you might consider.

I know pictures sometimes distorts things, but that stock appears to still have a lot of random sanding scratches which will cause that subdued or muddy appearance at times. I never used that chemical that you mentioned so I cannot comment on it. I use powdered stain that I mix with denatured alcohol to color the wood in gunstocks. I have also never been really happy with the effects of oil base stain on stock wood.

Not an expert with maple, but ...I'd say you need to try to get rid of all the pervious efforts..Wonder if Oxalic acid would clean it enough to start all over?

It is almost for sure western maple (Acer Macrofillum or Big Leaf Maple)very soft wood without much harness difference between the Fiddleback and heart wood so it doesn't take stain like Sugar or Red Maple. Doesn't show the figure well.
I used it for firewood when I lived in Oregon, excellent for that purpose, every once in a while I'd notice a fiddleback chunk going into the stove.

"Tiger Hunt". in PA used to sell Red Maple and Sugar Maple. Don't know if his web site is still up, or not. Got some extreme fiddleback from him in the distant past.

Aqua Fortis, maybe .