Right off the bat, the glaring problem I see is you are using CCI 209MZ primers with blackhorn 209 which are very weak. You really need a strong primer with BH209, and there are only two recommended. The Federal 209A, and the CCI 209M. CCI 209M are completely different than CCI 209 or CCI 209 MZ.
I have no experience with the Peregrine, but 150gr volume of BH209 in a 40 caliber is a really, really strong load. That's over max on most 50 calibers. I'm guessing the Peregrine is built to handle such charges, but I have to wonder if that is really the best for good accuracy.
There's really nothing new under the sun. Back in the 1800's, target rifles were often 45 caliber, such as a Whitworth rifle, but 40 caliber and other oddball sizes existed. I think this shows a discrepancy on what target shooters want, and what hunters want. You are shooting a 250 grain bullet, which is kind of light even for 40 caliber. But that and high powder charges gets you high velocity. On the other hand there were the target rifles, again I'll pick on the Whitworth, which it's bullet for a 45 caliber was 530 grains, and most people found best accuracy in the 70-90 grain range with blackpowder, maybe 100, also depends on powder grade. 70 grains was the standard from what I've seen for military use. This was in the 1850's, and used somewhat by the confederates in civil war. Not that it matters, but the union army was using breech loading Sharps rifles at this time, although they used linen cartridges, and still used percussion cap ignition. These were 52 caliber, 50 gr powder.
That might sound like a bunch of babble, and it kind of is for your purposes. Despite the Sharps cartridge rifles being an obvious superiority in war, just a few years later the USA government went to the 45-70 brass cartridge. A 405gr bullet with 70gr of powder. In 1879, the government did thorough testing with the 45-70, and other cartridges, at extreme range, 2 miles. These were the Sandy Hook tests. The results of this test had them ditch the 405gr bullet for a 500 gr bullet as standard, still with 70 gr powder. Sound familiar? Even today, the guys competing long range, or really any range with 45-70's BPCR, they are all shooting 500-550 gr bullets.
I'm not saying you need to be shooting 400+ gr bullets. What I am saying is the Peregrine, and other fast twist, smaller bore muzzleloaders are not new ideas at all. What makes them shoot great has been tested in the past, and will still work today. I'm guessing you don't have any interest in shooting really long ranges, and more into a flatter trajectory for hunting, but don't discount the tried and true.
