How much less than the advertised IBO does a bow normally shoot? I know there are a lot of variables to be included in this, but is there an average?

The Bowtechs seem pretty close. Each one comes with a "birth certificate" where it was chrono'ed with a 5 gpi arrow. The biggest deflater of IBO seems to be that fact that most folks don't draw 30"; and we tend to put stuff on our bowstrings to quiet them down that hurts speed. Not to mention the tendency to run arrows heavier than the minimum - to get better penetration.

The only bow I have owned that was weak on IBO was the Fred Bear Element I got for my son in 2006. Calculating backwards from the chronograph, I came up with an "real" IBO of about 290. Manufacterer specs were just over 300.

for a bow fully setup for hunting and an "average" shooter you generally loose 30-40fps off of IBO. thats "average" arrow weight, draw weight, legnth and string setups...sometimes more sometimes less...you shoot heavy arrows on a short draw and like a longer arrow and light draw weight, your going to loose more than the guy that likes a light arrow, as short as he can get them and shooting a maxed out bow...

30-40fps is usually pretty ballpark for a hunting setup though...

Mauser is pretty close form my experience 30-40 fps less would be close with a " Hunting " set up

my bt general shot 275 with 29.5"draw at 71#'s. with a 500(total)grain axis fmj with blazers and a whisker biscuit. i thought it was pretty good honestly. that is a heavy ass arrow. and on its birth certificate it said 300 even so a 25fps loss with that heavy hunting setup isnt too bad to me.

Yeah that is pretty downright smokin' if you ask me.... I have an Iron Mace (pretty much same cam system as your bowtech) that is doing 282 at 63#s with a 454gr ACC at exactly the same draw as you. I'm shooting 346grs right now at flat 60 and whipping right at 305fps hunt ready.

On my Legacey the IBO is 308 fps. I shoot a 28.5" draw and the best I could get out of mine was 294fps, shooting at 70# with a 28" 350gr. arrow, so I lost 14fps with a 1.5" shorter draw.of course my hunting set up is different, I shoot a heavier arrow.

I got 311 from a 370 gr arrow (292 with a 430 gr hunting arrow)out of my Ally after replacing my strings and cables with Vapor Trail and messing with the position of my STS (Birth Cert has 314 I think). Drop of the STS and I'm at 294 with the 370 gr arrow.Before string/cable swap and adjusting STS I was at 283 with the 430 gr arrow.

According to OT2 my adjusted IBO is 309 now. Before it was 304. The interesting thing I drew from this is from those numbers that my bow was not as efficient with the stock string/cables and the STS in the highest position as it is now.

The Diamond Marquis is ibo at 30" 70# 316 - 324 mine came with the birth ceritificate 311 60# 29" draw. for dropping 1 inch and 10# That isn't bad!

What effect does the STS have on the speed of the bow?