I do not have any data for the Banshee but I would warn you on trying to get 4000 fps with a 100 gr pill in that round. Basically the Banshee is a ballistic twin to the 257 STW and that round has been toted as a 4000-4100 fps round with a 100 gr bullet in a 28" barrel.
Sadly, this was spread around by irresponsible gunsmiths looking to make a sell and using exaggerated velcotity claims as a sales ploy.
I have built dozens of 257 STW rifles and in a 30" barrel you will top out at 3950 fps with a 100 gr pill. That is the absolute highest I have ever seen.
In a 28" barrel my customers were topping out at 3875 fps and in 26" pipes in the 3800 fps range.
Your Banshee cases may be able to handle more pressure then the STW case but I would be careful to watch your pressures as you reach the +3800 fps level and increase slowly from there on up. I would also recommend developing your loads in warmer temps because a top end load in cool temps will often be a dangerous load in warmer conditions.
I would also recommend you watch out for powder bridging issues in your Banshee. I designed my 257 Allen Xpress and 257 Allen Magnum and have seen this in both of these rounds using stick powders. The 257 Allen Xpress is based on a 300 Dakot case and for all intent and purpose, it is identical to the Banshee and STW in performance. All are within 100 fps of each other with the STW being on the low end and the AX and the Banshee being so close it would be hard to say which would be faster.
I highly recommend using ball powders for these rounds with this level of case capacity to avoid any powder bridging problems which can result in severe pressure spikes.
For the lightweight bullets, Ramshot Magnum would be a good one to try. But again without knowing the powder capacity of your Banshee for sure I hate to recommend any data.
My 257 Allen Mag is alot bigger then any of these and it HAS to be loaded with Ball powders to be safe, no stick powders will work at all no matter what burn rate they have but this round also has a 100 gr case capacity.
One more tip I would like to offer with the big 25 cal magnums, you will be much happier with your results and get fewer gray hairs if you increase bullet weight and forget about the 100 gr bullets.
When I started playing with the STW an then my Allen Magnum and finally my Allen Xpress, I wanted to see how fast the 100 gr pills could be ripped out of these barrels. They are fast but they are not nearly as consistant and on most cases accurate as the heavier bullets, espeically at longer ranges.
Even jumping up to the 115 gr class bullets really tames down these big cases.
Even better are the heavier 125 to 130 gr ULD RBBTs available from Wildcat Bullets. You will drop velocities to the 3400-3500 fps range but load consistancy will greatly improve with these heavier pills and on game performance will be taken to an entirely new level as well.
For long range hunting, the decreased wind drift is far more valuable then the slightly increased bullet drop.
I assume you have a 1-10 twist in your rifle. If so you can shoot anything up to the 130 gr pills.
If by chance you have a faster twist like a 1-8 which I am sure you do not have, there are even heavier bullets available which turn the big 25 cal rounds into legit 1000 yard hunting options such as the 142 gr ULD RBBT and the huge 156 gr ULD RBBT.
Simply put, the heavier the bullets, the more consistant your Banshee will be in most every case I have tested with this class of round.
All depends on the range you want to shoot and the purpose of the rifle as far as what you will hunt or shoot with it.
My favorite powders for the heavier pills in the STW and my 257 AX are AA8700, US869 and with the real heavy pills, WC872.
Good luck with your screamer!!
Kirby Allen(50)