D97 & B55 Experience

[BAbassangler]

What is your estimation for change in point weight, in switching from B55 to D97?  The reason I ask is my setup flies great but a little quicker would be nice.  45#, 29 3/4" 500's with 300 total PW, 565gr.

[Phil Magistro]

You didn't say what kind of bow. From my ASLs there is a very modest gain between D97 and B55. My recurves showed a little more gain for D97 but I have never seen a gain of 8-10 fps when changing.

I've recently started shooting B50 from my longbows and don't worry about few fps.

[BAbassangler]

It's a modern ILF R/D.  Everything I come across puts in terms of "a few FPS". What do you think that is, 25 grains, 50 grains?  Thanks for your input.

[McDave]

I don't understand your question, because changing strings has no correlation to change in point weight, unless you define one. For example is your question, "how much would I need to increase point weight to offset the speed increase from changing from B55 to D97?"  My guess is about 25 grains.  Other correlations are possible, but you would have to define the correlation you want to make before anyone could comment on it.

[BAbassangler]

Sorry to confuse. I suppose I assumed we were all starting with a perfect bareshaft, and when going to a faster or slower string, what would be the new point weight to keep the same perfect bareshaft. Does this help?

[McDave]

Sorry to confuse. I suppose I assumed we were all starting with a perfect bareshaft, and when going to a faster or slower string, what would be the new point weight to keep the same perfect bareshaft. Does this help?

Yes, thank you for clarifying. I understand the question now. The most common figure I hear is that a change of strings from B55 to D97 will increase arrow velocity about 4-5 fps. To put this into perspective, this is similar to the increase in arrow velocity from going from a static release to a dynamic release, or perhaps from a longbow to a recurve.  Of course this will vary depending on individual circumstances.  However, the change in arrow velocity is often enough to require a change in arrow tuning, which includes point weight.

The problem is that the effect on tuning from a change in point weight depends on where you're starting from. My experience is that the effect of a change in point weight is more proportional than absolute. For example a 10 grain change in point weight makes a noticeable difference in tuning if you're starting in tune with a 100 grain point. A 10 grain change in point weight makes a negligible difference in tuning if you're starting in tune with a 200 grain point. Probably you would have to change point weight by 20 grains to get the same difference in tuning if you're starting in tune with a 200 grain point, but I'm not sure if the relationship is directly proportional, just that it requires more of a change as the starting weight increases.

So it's difficult to answer your question, because the answer changes depending where you're starting from.

[BAbassangler]

Ahaaaa...so it's like adding a tsp of salt to a cup of soup vs. a crockpot. Gotcha; maybe I'll plug some numbers into the spine calculator and see what change in point weight give me the "few feet per second" everyone reports, and do a little comparison experiment when I get a D97 string together. Also give me an excuse to break out my new-in-box chrono that's been sitting in storage since covid.

[McDave]

Ahaaaa...so it's like adding a tsp of salt to a cup of soup vs. a crockpot.

Good analogy! I think in the case of cup vs. crockpot, "less is more" would probably apply, meaning that if you multiplied one teaspoon X the increased volume of the crockpot compared with the cup, the soup would probably end up tasting too salty, because of the mysterious alchemy of the cooking process. 

Something similar may be going on here, which could make the actual ratios of the two beginning point weights an imprecise indication of what effect on tune the addition or subtraction of point weight after changing the string would have.  For example, the differences in total arrow weight might also affect the results.  Fortunately, we don't have to be that precise.  In the tuning process we can just keep trying different point weights, cut, change spines, brace height or string silencer location until we stumble on something that works.