The rifle is a Ruger RSM, originally a 458 Lott, now a .495 A-square and ballistically a 500NE, 570 grains at 2,150 fps.
In this chambering, it will never wear a scope. As a Lott, the Ruger stock worked with a low mounted scope, but the open sights were a challenge. The common American stocks produced today give about a 60% butt plant on my 6'2" frame. Ok for a 270 WSM, but not a 500. I have the rifle, a tough piece of walnut from Calico, a great carver, but how to get the specs right. I've worked my way through the rifles on my rack. An old FN or Husky give a hint, my Sedgely '06 is close, coming around to the shotguns, a Bereta 391 has enough drop to plant 100% of the butt on my shoulder, cast-off to align my eye, and good drop at the comb but the LOP is a little long.
Am I on the right track to shock a stopping rifle.

Look at the rear of a Asquare Hannibel for a exceedingly wide butt configuration. With a good leather covered recoil pad this does wonders to reduce felt recoil. If done properly it winds up looking decent and if necessary you can add lead to the butt and under the forearm to balance properly. Gun should recoil straight back and not up.

It's the "straight back thing" that I take to imply a straight stock, little or no drop. That stock will not plant on my shoulder and still align my eye with open sights.
What measurements would H&H take to custom fit a stock and what is the criteria for a proper fit for a stopping rifle.

Ask Ray Atkinson here on forum--

I know he gets shit from some people, but I have two rifles stocked by him and they are an absolute joy-

Fit both scopes and irons--

Have had nothing but good results when woking with Ray.

For an iron sighted rifle a straight stock is not recommended for quick pointing sight alignment and it brings ALL the recoil straight back into your shoulder..

I would have drop at the comb and drop at the heel divided and expect it to split the difference in upward recoil and straight back recoil, compensate it at the comb to protect the cheek. and rather than measure the comb height, actually close your eyes and point it, open your eye and see if your dead on at 50 yards or whatever..cast off is particularly important for pointability and recoil with a big bore IMO. Cast of depends on the shape of your face, and for that reason its always best to judge by the owner testing the pointability before the rasp hits the wood. Other options but these seem to be the most useful IMO.

Thanks Sean, appreciate that.

Ray-thanks for the comments. You have more or less confirmed the direction I was headed. The stockmaker is Glen Morovitz and I have previously worked with him, a nice guy and magic with wood. He will be walking me through all this, but we probably won't have an opportunity to get together so I will own the final measurements.

Why don't you have Glenn build you a pattern stock and send it to you for testing before he builds the actual stock? I do this with clients fairly frequently. It adds a few dollars in shipping and a little bit of time but well worth it on a high end re-stock. Best of luck.
Steve

For the big bore addict or shooter of custom rifle, having ones own pattern stock is a great idea, most smith will turn you a fitted pattern for about $150 dollars and they might even furnish the wood. if not then a pattern blank shouldn't cost hardly anything. A pattern blank takes some wear as its glassed over and over again but done correctly it should be good for a hundred guns I think?

I found a book called "gunfitting" which is a good read and very helpful. Frankly, I've heard "straight stock" so much I was questioning my own needs. No straight stock fits me worth a sh...
With a scope sighted, light kicker, I can live with it but a bigger bore, no. This rifle stock will fit like a good shotgun.
I'll talk the pattern idea over with Glenn. If he thinks we can hit the target without one, I'll go with his thoughts. I'm getting close with the measurements I will suggest. The list is getting pretty long.
FOREARM I like them short and full, slightly pear shaped. My hands are large, but not LARGE.
GRIP not as open as first assumed, enough to keep the second finger from the trigger guard, and land the sweet spot of my trigger finger on the trigger, but too open doesn't give me the natural grip angle my hand is comfortable with. The grip should flow to the cap without an inward curve that crunches my fingers together and be 2" wide.
BUTT the butt will be sized to use a full Kickezz large recoil pad, 5 5/8" X 2". LOP will be 14+", drop at the heal will be 2 1/2+ inches. This gives me 100% butt plant on my shoulder. The comb and comb height are works in progress. Drop is getting there, but the steep angle from the nose to the butt is leading me to consider a semi monte carlo style. The winchester late 90's .458 and .416 classics fit pretty well with this feature. The position of the comb nose relative to the grip shape will keep my thumb comfortable as it crosses over the grip.
CASTOFF some but how much and heel/toe relationship? My only example is a beretta 391, with the max castoff shim in place and it points very naturally.
There you have it. Thanks for input, I find a little gem often.