rt_con
rt i know you were asking Grouse but if I might replay I would indicate to you that T7 and BH potentially and especially with the lighter bullets create the same velocity. I know some have claimed better accuracy and that is totally possible also because BH is going to cause a different 'harmonic' in the barrel than does T7.
The difference T7 burns really fast - it reaches peak pressure sooner and higher than does BH. BH is a slower buring powder and it will not reach the peak pressures that T7 does because the bullet has already traveled further down the barrel increasing the volume of the cylinder that is containing the pressure. Now the converse of that is also true. If you measured the total pressure of 100 grains of T7 and 100 grains of BH - BH is going to create more pressure in a contained cylinder.
I had load combinations that were very accurate with as little as 85grs of 777... needed to be increased to 100grs of BH209 to maintain that same level of accuracy.
There is really now way to tell with out shooting.... BH buring slower will create a different barrel harmonic that the faster burning T7. This will be very evident as you increase the weight of the projectile. Barrel harmonics will also change with the weight of the projectile. Lots of things effect accuracy and I feel the vibrations step up in your barrel are the least controlled variation there is. You just got to test and see what your barrel and stock like.