Well.. I've never shot a vtr .223.
But I have shot various bolt action .223's (including other remingtons)
55 grain is the cheapest and most available.
If you want to shoot it a lot, site it in for that..
If you want a target gun try 65-73 grain bullets.. they stabilize farther out and group well at 300+ but realize you'll be spending a bit more every time you go out.