First I did some looking around.  There's actually one (good)recoil pad made to fit A1/A2 stocks, but it's got mixed reviews on fit problems.  Got hold of these folks who say it's been improved.  I've used that brand pad before, and they're very good.  However, being cheap and thinking I had something in a box somewhere, I kept looking and finally found it: a Pachmayr 'grind to fit' pad, last of several I'd picked up on clearance a few years ago.  I'd used one to fit onto the Mosin-Nagant stock, and it worked very well.  So, try to make it fit; here's how it went.

One thing to remember: all grind-to-fit pads are not the same.  This one has a hard plastic base, and you can cut it down a LOT; some are made  in different sizes and have a steel plate embedded in them(I believe the Limbsaver pads are one).  Check the information, if it's one of these it should note how big it is, and just how far you can grind it down without hitting the plate.

More than just grinding the profile in this case, as the original buttplate is cut in so it has a base that fits inside the stock.  More on that later.

Original and Pachmayr

The original butt plate helped a lot.  Set it so the top screw hole was centered on the top hole in the pad base, centered the plate on the pad,

then clamped it.  Now, hopefully without it moving(things can be sneaky that way), trace around it with a sharp scribe to scratch a line into the pad.

Here's the most messy part.  Grinding to that line.  You can use a grinding wheel, or a belt or disk sander, if the belt or disk use a fairly coarse belt to do most of it.  That(or the wheel) will cut pretty quickly and tends to throw the pad bits off instead of clogging.  You will have black(or red, or whatever) rubber dust all over, which is why I do stuff like this by putting the sander outside, and then blowing it off thoroughly before putting it back inside.

Cut away rubber until close to the line, at which point try it against the original plate to make sure you don't overdo it.  If you need to redo the guide line, on a plastic plate like this you can rub it lightly on sandpaper or the belt

to roughen the surface a touch; that'll obscure the original line and let you scribe a new one.

Now take it down to the line.  The ideal is that JUST as the line disappears, you're there, which means do that last bit very carefully; cut and compare.  If need be you can leave it a touch oversize and clean the rest later.

Ok, you've got a good match. 

Now you need to drill the holes for the screws(done in the pic above).  Not something you have to do with standard stocks, but  the A2 stock uses two with large heads, and they can't just slide in like the regular type.  Here I put the top screw through the original plate and into the pad hole to make sure it wouldn't move(base to base), lined the edges up and clamped, then used a drill bit that barely fit into the other hole in the plate.  Push it in to contact the pad, turn it a few times and it should mark the pad base nicely.  Then take it apart, place the proper bit in the drill press(can be done by hand, just watch the angles), and taking care to keep things square, drill all the way through the pad, using the top hole and the mark for the bottom for location.

Flip it over, and use a bit just a little smaller than the screw heads, drill down far enough to cut most of the rubber but not into the plate.  That should let the screws anchor the pad solidly.  With the regular type screws for this you can get them in pretty much invisibly, but I wasn't concerned about that here; with those big heads, it'd never work.

Also: for the above I used brad-point wood bits; they have spurs on the outer edge of both cutting flutes to make nice, clean holes.  If you don't have/don't want to buy one, a regular bit of the same size will work, but won't give as clean a hole.


Now you need to cut that lip.

Yes, can be done by hand, using a sharp file.  No, I didn't.  Saved by a piece of equipment I bought on sale a few years ago at Harbor Freight: a trim router

(please ignore the stuff in the background)
This is a small router intended to trim, say, new linoleum topping on a counter to the exact edge of the counter very cleanly.  Works for other things as well, for instance the pistol grips I orignally bought it to work on; you can hollow out an area in the center of a piece, or shape a grip base like we're doing here.

It came with, among other things, a roller guide

Idea is you adjust that so you can roll the guide along the counter edge and it'll trim the new top to exactly match.  Used the original buttplate to adjust the width and depth of the cut

and locked that in. 

For the cutting, I strongly(VERY) suggest you find a way to lock the router in a vise, or in some other way secure it, so it can't shift and you have both hands free.  And be very very damned careful; those sharp edges are moving at many thousand RPM, and if you slip into it, it will tear you up.
I'd also suggest earmuffs and safety glasses; this sucker is loud, and it'll be throwing small thin slices of the plastic base around.

With it secured, and you protected, power it up and- carefully- work the pad base on it.  Remember, this is kind of like a buffing wheel in that it can- will, if there's a chance- grab things out of your hand.  Work all the way around.  If, especially on the top and bottom, there's a place you can't really get to, don't worry, cleanup can be done with a file.  You wind up with something like this

That area at the lower right that looks uneven?  That's because it is; the bit grabbed it, which resulted in swearing and that choppy area.  There was a small area at the toe that the bit couldn't reach, so used a sharp file to cut that to fit.  You'll also notice that the white showing isn't perfectly even; I didn't get the sides of the pad all around exactly square to the base, therefore I wound up with slightly uneven edges.

When done, it goes on like this

Not bad.  The profile wound up fitting the stock very closely.  Maybe a little file work on a couple of spots and that's it.

One thing you have to watch with a AR is you do not want the top screw- which screws into the back of the buffer tube- to go in too far(shut up, I know what you're thinking and you're sick).  Some measuring showed no problem there, it'll actually go in less than with the original buttplate.

Result:
Tried it out at the range; HUGE difference.  I know .338 Federal isn't as punishing as a lot of cartridges, but that flat buttplate beat on my somewhat-abused shoulder more than I was comfortable with.  Worth every bit of the work.





If you're looking for that 'can't feel the transition' fit, the process in short is
Grind the pad very close.
Install.
Wrap a turn of strapping tape around the stock with the edge meeting the pad edge exactly.
Take a SHARP, NEW file(gunsmiths tend to have a file just for this purpose), and start cutting the pad sides down. 
When the file touches the tape, stop cutting.
Replace the strapping tape with masking tape, and repeat.  Do it right and you'll wind up with no scratches on the stock and a very nice fit.