I'm sure this topic has been posted a biz zillion times already but it's new to me. I've narrowed it down to 45-47#s. I've got 7 or 8 bows at any given time from vintage to new hybrid LBs and second only to the grip I was trying to determine why some bows tune and shoot better. My newest purchase a Dryad ILF longbow really helped with this revelation. At 51#s I couldn't get bare shaft to tune for nothin, but when I turned it down to 47#s perfect. So I decided to check all my bows, and my favorites fell between those weights. Wouldn't have thought a couple pounds would make that much of a difference!
Are you using arrows rated for that 51# bow weight with the shelf cut and all figured in? I cant see why you couldnt tune a 51# bow in but you can a 47# if you have the correct arrows and such. I know for some 5# can be the difference between being over bowed and not over bowed, is that the issue?
I own a nice range of bows 46-65 and somewhere between 45-50 is a nice combination of all day lightness with some measure of power. get the right bow at that weight with the right limb design/material and you can make the weight go real far for you as far as fps/ power. My Holm bows for example illustrate this, one's 46 the other 47 but man are they zippy and have nice punch.
I believe that every bow design has its optimal weight. Some cuts of longbows, even Hill style longbows, have efficient weights that will vary. As an example, the same heavy limbed design at 85 pounds can be a powerful magic wand, thry to copy it at 45 pounds and it can be a wobbly slow shooting mess. Or on the other side take a shorter trim limbed 50 pound bow, build something similar, but 30 pounds stiffer and it can be a shocky, stacking dud. then take the same idea, lengthen it a bit go for something 15 pounds heavier and pure magic happens at the same draw length, change that draw length and you could end up with something completely different. If there were such a thing as one perfect design that was perfect at the any draw length and the same for any weight, we would all be shooting the same bow. viva la difference
Possibly varies with your own physiology and certainly bow design. My two best shooters are 51#@28" (62" recurve) and 50#@28" (66" recurve) that I draw to 29-1/2".
But I'm hoping to take a 47#@28" (58") recurve into the woods next year. Weighs about half as much as either or the field/target bows above.
I think for me it's simply the weight being too much I can't hold that split second and it mess's up my form. I shoot 3 under and line up the shaft to my target, if the weight too low it feels like I pluck the string. I'm sure if I work myself up I could be just as accurate. Guess its what I'm used too.
I had a Bob Lee hunter that was perfect at 47#. Now I'm shooting a Hoyt Buffalo that's pretty good at 50#. I only draw to about 26.5" so I'm shooting about 45# likely, though I have read that Hoyt's typically run heavier than marked.