Another beat to death topic, but my research shows conflicting info. Haven't really nailed it down yet. I just got a Bear Montana 45#@28. My actual draw length (measured three times to be sure) comes out to 28 1/4 inches at my anchor point. I plan to hunt with Simmons 165 gr Sharks. I'd like to be able to use wood arrows but may also play with aluminum and carbon. I've read/heard that you need to go up to the longer length if you are between draw lengths, so I'd need to use 29 as a draw length? I've also heard that I need to go 2 inches longer on an arrow shaft and there are those who say one inch is enough. What is the consensus? Then, there is the school of thought that if you shoot a point weighing more than 150 gr, you should go to the next spine size, like from 50-55 in wood, to 55-60. I'll welcome all suggestions for a starting place. I hope that will make the process of getting dialed in easier. Oh, I plan to hunt white tail and the occasional hog with this rig at no more than 15-20 yds. Not new to archery, just longbows.
There's a lot going on here .........
2 inches longer but 1 inch is enough, I believe if you've heard that it's reference to clearance off the riser at the back of the bow (hand clearance). That is all up to you and what you are comfortable with, having a broadhead potentially draw back past your index finger. My opinion (that's all), is there's no need to have a ton of arrow past the riser at full draw, just enough to be safe and your arrows flying right.
I draw 27 on the nose and shoot a 29 inch wood arrow. I shoot 46# at that 27 inches. My wood is spined 55-60 (all hand spined closer to the 60 - 58, 57 and such) and I use a 125gr broadhead with that and get perfect flight.
Going up in arrow length if you are in between draw lengths - don't think of it like that. Think of SPINE! Usually you hear "going up" (in spine!) when you are at the edge of a draw weight range.
Arrow length is arrow length ...... once you know your draw length, decide how long you want your arrow past the riser at full draw, then start predicting the spine that is going to work for you at that length, with whatever point weight you choose to use. At least this is how I do it with especially with wood. Carbon is a little different and my carbon arrows are a half inch longer than my woodies.
For wood, a fantastic tool to have at your disposal (aside from a good spine tester, everybody should own one if they shoot arrows), is the test pack ..... Surewood Shafts test pack, 4 shafts in 3 spine ranges. Pretty much a must if you want to find the perfect flying wood arrow and know the best spine for a length point recipe. Hope this helps you even if just a little bit. Good luck with your tuning and keep it fun as it is supposed to be