i was wodering if anyone has tried using under 90grs of bh209 and how did it work

depending on the projectile, 90gr or under can be just as accurate as 100-110gr. All my guns however do prefer the 100-110gr charges.

FG (& anyone else),
Are you measuring the BH 209 by volume or by actual weight? Saw a chart that stated 100gr of BH 209 by volume was only 81 +/- grains by weight.

I just started shooting the BH 209 and been using a volume measure of 100 grains. Seemed to do fine in my rifle (great accuracy), but I do have to say it seemed alittle soft recoil wise.
Have a couple of potential deals going on my projectile of choice (THORs), so maybe I can work up some loads by weight to see if accuracy is effected and at what load does accuracy become unacceptable.

When most folks just call out "I am shooting 100 or 110 grains of ..." they are talking about volumetric measure. There is a chart on here somewhere that gives volume to weight in grains conversions.

FG was talking about volume measures in his post above.

volume.

Blackhorn209 website has a conversion chart with volume/weight.

100gr Volume is actually 71 grains by weight.

Here is the conversion chart posted by Western powders.
http://www.blackhorn209.com/wp-content/uploads/2010/12/b209muzzleloaderdata.pdf

I've been shooting 90g at the range and had some very good groups with it....wondering how effective that load pushing a 250gr slug will be on deer.

some of the best groups were with 90 grs. but I would give up a real tight group for more FPS.

I would think it would depend on your hunting distance, size of deer in your area and bullet weight. Assuming accuracy is OK with your combos.
I have used the following site to get relative differences between bullet weights, power charges /velocities/ energy. http://www.bpishopping.c
ASSUMING THE SAME CHARGES
Lighter bullets will be faster with less long range downrange energy
Lighter bullets will generally shoot flatter but will lose speed and energy faster.
lighter bullets will have a lower ballistic coefficient which does not help long range accuracy.
Many folks feel that 1000 foot pounds of energy is needed to bring down a deer.
So if your hunting is in the 50-100 yard range several combos will suffice, if above 100 yds you have to be more concerned with wind drift, drop and final energy
You may not want to use Powerbelts but the relationships should remain the same. Other bullets will have different bottom lines.
BULLET PLACEMENT IS STILL THE MOST IMPORTANT.

90 grains is plenty. My dad shoots 80 with a Speer 45 colt hollow point at 1500+ fps. Devastating on deer. You should know that BH209 really shines as the bullets get heavier. I was shooting a 325 grain XTP at 1791 fps with 100 grains & as I was chronographing various weights of bullets I could see the efficiency improve as the bullet weight increased