Since Im somewhat new to trad someone help me with this. Buddy of mine has and old Indian recurve. What will happen if he puts a fastflight string on it. Also can you do anything to and older bow to make it fastflight safe?

I am new as well but from what I gather the limb tips have to be reinforced for a fast flight string.  If the tips are not they will fail.

I would not mess with the fast flight strings on any of my old bows. I don't thinks that the gains are worth the risk to the bow.

Another guestion, how do you know when a string needs replacing? Does it wear on the ends? I keep mine waxed so I don't see any fraying.

You could rip the tips right off the bow.        Fast flight doesn't stretch like dacron. Picture this dacron= sewing thread and fast flight = piano wire. If the bow doesn't have reinforced tips it's like playing Russian Roullete with your bow. Only a matter of time before the tips are damaged. As far as changing your string. Depending on how often you shoot. Usually a good B-50 should last you a season. Buy 2 strings, break in the first one so it's all stretched out. Take it off and put on the new one.Put the original in your bow case with a stringer. That way you'll always have a broken in spare in case of an emergency.

It will shorten the life of the bow.Not worth damaging the bow,a recurve limbs are thinner and could cause more shock and vibration to the limbs.I like to shoot endless loop dacron on my older recurves,but never shoot a modern low stretch string material.

According to some bowyers a string shold be replaced after one year or 10,000 draws. wheither this refers to FF strings, Dacron strings or both I could't say but it's a good idea and safe practice to get into. And if the old string is in good condition I keep it as a spare.

NO!