Neck sizing is only done with cases fired out of your particular rifle. You can set up an FL die to neck size only, but it's a lot of trial and error fiddling to get it right. Plus, as mentioned, you'll have to FL resize 'em again eventually.
You should be able to see by eye where the sizing stops on a case. If it's not right where the neck meets the shoulder fiddle, some more. You're looking for a slightly polished appearance. Might be a wee ring(don't worry about that).
Like emcon5 says, how you size has nothing whatever to do with the load used.
"...getting 1 inch groups with FL off a bipod..." Neck sizing isn't going to make anything better. .223 brass is cheap and readily available so it's neat and all, but not really necessary.
You should be able to see by eye where the sizing stops on a case. If it's not right where the neck meets the shoulder fiddle, some more. You're looking for a slightly polished appearance. Might be a wee ring(don't worry about that).
Like emcon5 says, how you size has nothing whatever to do with the load used.
"...getting 1 inch groups with FL off a bipod..." Neck sizing isn't going to make anything better. .223 brass is cheap and readily available so it's neat and all, but not really necessary.