So it looks like the 400 spine arrows are working in my 50# recurve. The old arrows were 447 grams with a FOC of 15.4% (at 32.5 inches long); the heavyweights (added 100-grain brass insert, plus 75-grain adapter and 225-grain field tip) come in at 679 grams with 28.75% FOC (at 32 inches). Flying pretty well with slightly over 1/2-inch cut off the back and I added a piece of toothpick under the arrow shelf pad. Brain working arc adjustments pretty well up to about 30 yards after shooting 300 – 400 arrows over five or six practice/tuning sessions to date. Thanks for the help y’all!