I don't know what wood you are dealing with, but surely it isn't walnut. You don't get much, if any, blotching with walnut. However, a lot of the lower cost woods that have been used for military and civilian gunstocks will blotch badly. Mostly those woods are, when unstained or unfinished, whitish or light tan or brownish. If that's what you have, blotching is likely to be a problem. Minwax sells a water based stain conditioner that they say helps control blotching, but it doesn't work that well. From what I've read and experienced, the best blotch preventative or controller is to use a 1# cut of shellac on the bare wood. Sand lightly after it dries and then use your stain. That works Ok, but the remaining shellac limits the penetration of the stain (which is the reason it prevents blotching), so you may not get the wood as dark as you'd like. I'd suggest, as an alternative approach, that you go with a non-penetrating wipe-on stain. No penetration, no blotch. You can add more later to darken further with it or you can use mineral spirits to take some off if it's too dark. Once you have it the way you want it, get some spray shellac from Home Depot or Lowes (or Ace) and give it one or two very light coats. Once that's dry, you can varnish over the shellac. The shellac prevents the varnish from dissolving the stain, which is just sitting on the wood surface. Minwax Fast Drying Polyurethane in Satin looks pretty nice as a final finish, and you can spray or brush it on. Go with light coats, so that the varnish won't drip or run.
If you apply the wipe on stain with a bunched up rag, you'll be amazed at how you can make it look like wood grain. Play with it till you get the hang of it. Mistakes come off with mineral spirits. I did all of the above a few months ago for a friend. Had I known how bad the wood was, I'd have not done it. But once I started I had to finish. The painted on wood grain worked so well that they thought it was a walnut stock.