Re: pressures.
First of all I am no Muzzle loader shooting expert but I have done a bit over the years and I have done a pile of reading on B P shooting, mostly cannons lately but B P/Muzzleloader shooting is mostly the same from 1/2" bore to 3" bore.
Firstly I know of no outwardly "visible" pressure signs that we can see, specifically the first sign that you can plainly see is a destroyed gun. Luckily, with BP, destroying a gun, while possible to do, it is very hard to do without extenuating circumstances like "tight double balling" or "short seating" a ball. There is often a reference to "over powdering" that is claimed to be easily seen by un-burnt powder kernels on the ground (more on this later) but this doesn't signify a pressure issue at all.
I am not suggesting that over-pressure isn't possible with BP (after all the US navy blew a 16" gun turret apart with some one time), just that it is hard to do. Your ball tightness or weight (as in double balling) will dictate pressures just as much as the powder charge. The US Parks Service commissioned a 'small arms & cannon" test for BP pressures in small arms used at re-unions & N-S re-enactments. Very much better testing equipment was used than was available when BP was used extensively. They discovered that, while "usual circumstants's" use of BP produced pressures under 23,000 (your is quite likely under 18,000), it was , with tight or large overweight projectiles, very easy to produce 30,000 or more. The US navy claimed that testing with the newer testing equipment after the turret explosion, that their big guns could easily surpass 100,000 flbs under certain conditions. In the middle of the civil war, a bunch of Lincolns war cabinet was attending a new, very large Columbiad" gun demonstration (I think it was a 55 lb powder charge) and the gun destroyed itself along with many of the observers ... Your Muzzle loader, with the charges offered up by folks here, with "normal ball tightness seated "on the powder" is probably in the 16-18,000 range.
The other "gun destroying" condition that the experts claim is the "short seated" ball. I and others have theories on why this is a "thing" but I don't know of any scientific testing that has been done under these conditions, probably because it would destroy some very expensive testing equipment on something that is already well know to be a fact. My theory is that the powder expansion reaches full force in the larger chamber before the projectile has a chance to start moving, producing a higher than normal curve than if the projectile starts moving as the powder ignites and continues to do so as the pressure curve increases. The fact is that I have looked at dozens of photo's of vintage cannons that have come apart under pressure and vitualy 100% are destroyed somewhere ahead of where the powder chamber would be. The theory being (and it is mentioned in Civil War Artillery training manuals) is that, under battle conditions when rapid fire is appropriate the powder charge is rammed sometimes with a live ember still in the bore or touch hole, if it doesn't ignite immediately it will when the projectile is started to be rammed, the rush of air from the ball seating fans the ember and sudden firing occurs, and photo evidence shows that the gun comes apart where the ball was in the tube at the instant of firing. The Artillery regiments of both side had a man on every gun crew who's only job during battle was to plase his thumb as tight as possible over the touch hole to try to mitigate the air rush as possible,lots of times it didn't work...many civil war artireryist went home without a thumb...but they were the lucky ones, most of the other gun crew would have lost arms or been totally dead from such a mishap. I will add here that civil war artillery gun crews were expected to fire at a rate of at least 3 round per minute (not much time given to properly swab) and now after the US parks service testing, they have set a regulation, along with a host of others, of at least 3 minutes between rounds at any public or private function.
Concerning "un-burnt powder kernels", it is a common statement heard or read that "BP cannot be over-pressured because the over-powderage will just be blown out on the ground. I have read (I have it here somewhere in my mountain of literature on cannoneering) that the British Navy did some BP burning & pressure testing back in the 1870's with more modern equipment than they had available before then. They claimed to have proven by these tests that all BP was burnt in the first 16-18 inches of barrel length regardless of bore diameter. That is not to suggest that pressure or fire isn't present as it is ( I have slow motion camera photo's of a 15 ft fireball coming out of the bore of my full size cannon). Part of their testing included cannons regularly built and some of the same bore dia. and length only the tubes were cut out with long ports allowing pressure relief after 20 inches or so. The claimed that, with the same powder charge, the same velocity of projectile was attained with both cannons, even the one that had no pressure detainment after 20 inches. I have seen the black dots on snow from a muzzleloader that for years BP manuals have claimed is "un-burnt powder" but this long forgotten British testing suggests that it might just very well be all burnt carbon flecks...you be your own judge.
All this to say that quite likely you will have to try too, on purpose, increase BP pressures to a dangerous level.
Seriously though if I were going with printing the smallest groups I could then I'd tend to opt for the patch lube which does not change after the first clean bore shot of the day. And that would be dry cloth with the Moose Milk. 3 drops worth per patch and the ramming stays very consistent. Then it's just a case of finding the ideal patch. Because patch fit and thickness does count in the accuracy at LEAST as much as does the ideal amount of powder.
