You might be interested in the saga of loading for my new rifle which after a wait of just over two years, I have at last got my hands on my new small frame BSA Martini with thick walls in 5.6 x 50R.
I already had 100 RWS once fired cases F/L resized in a Forster Die but when I tried them in the action the Block closed with difficulty and I had to use a rod to get them out.
Then tried some Fired S&B cases from my H/H single shot and they also wouldn't Load. 
I tried a factory S&B round which fed and extracted ok.
I then put half a dozen of the original F/L resized cases back through the die with the die as close as it was practical to the shell holder but they still would not extract.
As I was using a 357 Mag shell holder thought this might be the problem and then measured a dozen of the various shell holders I had and found they came out at from .222 to .250.
The shoulder of factory unfired rounds came out at 2.635 to 2.636 using my Forster 8.30 Comparator and the shoulders of cases F/L resized the second time were 2.642.
Took a little off the top of the shell holder and all ok.

I've had similar issues with occasional shell holders. I just put them on my belt sander and worked the top surface down. The top surface isn't critical enough to have to be perfect. The die just contacts it, so if it's not perfectly true, it wont affect function.
I always thought shell holders wouldn't affect sizing that much, but occasionally they do.

Boats,

Could you post a photo?  Certainly cheaper than a real tool post grinder.   

Dave

UtahDave, if you have a surface grinder with a magnetic chuck, they should be easy to hold. 2 options are, 1 hold it with a good quality vice. The other option is to block it in with some parallels. You would probably want to use 3 parallels to block the shell holder in. Lay the parallels down so that the ends form a V and set the holder into the V and use the 3rd one to lock the holder into the V. This should hold it fast and help to prevent it from turning. One other option to keep it from turning is to use the parallels in combination with a piece of double sticky tape, use the tape under the shell holder only. But use the parallels to hold it in place. 
Hope this helps, and for reference I had worked for 21 years as a tool maker with many many hours doing surface grinding on all shapes of parts.
Sam

Sam,

Thanks for the good advice.  I'm not much of a machinist but I will try.  I wonder if I could bolt the holder through the center to a piece of steel and hold that in the magnetic base?  I've had a few small pieces go flying so I'm a bit gun shy.   

Dave

Dave, you gave me a chuckle, yep when they go Zing-Bang, and you spend the next hour cleaning your shorts and looking for that part, yes it makes you a bit gun shy. Been there Done that. 
Yes if you take a flat piece of steel and drill and tap it, and then use a flat head or perhaps a button head cap screw to hold the shell holder down, that would give you lots of holding power on the magnet and should work quite well.
I can tell you that it is rarely any fun working on a grinder with parts that will not stick to a magnet. I have done my penance with things like that. I have at times ground parts made of solid carbide that has about zero magnetic properties. Eventually you become a bit creative in finding ways to hold the parts. It becomes even worse when the parts are long (2+") and thin (.020) or so and you have to hold .0002" tolerance and they have to be flat, absolutely flat. Kind of glad I don't have to do that stuff any more, but am more than willing to share what knowledge I have with others.
An example is here, another is, if you look in the sale section, guys were looking for front lock rings for a Lyman STS scope. I ended up accepting the job, but one member wanted to know how I made the part, I explained it to him, and he was greatly appreciative and hopefully will take that tidbit of knowledge and expand on it to improve his own skills.
Good luck with the grinding. Your fortunate to have a surface grinder to do things with. There is just so much you can do with one if you have the right tooling to go with it. If nothing else they are wonderful for making radius lathe tools and sharpening threading tools.
Sam

I've had this problem with 22Jet ,   just took off .015 thou off the bottom of size die,     I had to take down 25-20 dies as well  to get proper sizing..   think about it...