Taking into acount the age of the bow and type of cams it probably has on it (assuming dual medium cams) I think the spine should be good on those arrows. The fact that they are the correct length helps alot. When you said they were 31 inches long I was a bit thrown off. As far as the weight of the tip goes I don't think it will really matter much. 100's are easy to find and should still give you decent FOC. It would depend on the type of fletchings you have as well (feathers or vanes), you didn't say which you had.

My only concern now is that these arrows are kind of light. Depending on your fletching you are shooting between 5.6 and 6 grns per pound with a 100 grn tip. While you should pick up some speed this way, I'm afraid it may be a little hard on this old bow. 6 grns per lb isn't bad though, epecially if you don't shoot alot. I would highly suggest limb savers and some good string silencers to take some of the vibration out after the shot. Keep your string and harness waxed well too.

If you have some 125 grn heads left over try them and see how they fly. If they are pretty old keep in mind some of the newer low profile heads fly a bit better. My suggestion would be to fletch these arrows with 4 inch vanes and some offset, unless you have a drop away, then go with helical, and use a 125 grn head with good penitration qualities. This would give you a finnished arrow weight of around 350 grns and an FOC of 13 - 13.5. Plus it would up your grns/lb to almost 6.5 helping relieve some of the stress from your bow.

Don't get me wrong, I'm not saying your bow will self distruct if you shoot these arrows out of it. That's not the case at all. However if you shoot a lot, over time shooting light arrows can take a toll on your bow. Worn bushings, bent axle's, cracked limbs, that sort of stuff. If you don't shoot very much, or are considering getting a new bow in a few years I would not be overly concerned about it. Now if these arrows were under 300 grns I might be a bit more concerned. Don't go with feathers and a 75 grn tip for a set up. You would pick up some more speed, but most likely quite a bit of vibration and noise to go with it.

And I don't claim to be an expert at this either. I don't own a shop or anything like that. Just play alot and read everything I can. I do however spend alot of time reading things on the internet and talking to shop owners. I also experiment quite a bit with my own set up. So I'm not completely clueless. Since no one else was telling you what you wanted to hear, I decided to give you my opinion. And it's just that, my opinion. If Len or someone like that comes on here and says I'm full of crap and all wet, I would go with what they tell you. They have a lot more experiance at this then I do.

Also if you would like some more info on set ups and arrow spine type stuff I can give you some links and right down what I think about the subject. It may take me a while, but I'm unemployed at the moment so I have time.

The short answer is if you can get good groups with those arrows with 100 or 125 grn tips your set up is more than capable of killing deer. I think the spine should be ok with either tip weight. If not you can fine tune it with your draw weight if you have to. Have you looked at the easton tuning guide yet?

Good luck,
Paul