I don't know that fear is the right term when talking about the so called "magnum" loads of 150gr. Many have tried them but only a few have found them as accurate as something a little less punishing.

As a reloader you have probably found that some load combinations work for one gun but not another. Same thing when trying different powders with a paticular bullet. When loading a muzzleloader you are, in effect, reloading for each shot in a similar manner to reloading for a CF rifle, just not in advance.

Each gun is going to react to each load in a unique way. You may find a load for your gun that works at the max load allowed, or you may find it likes something less than max. When I reload for my CF rifles or load my MLer's, I prefer accurate loads over screaming fast loads. If I find a load that does both, I'm a happy camper, if not, I go with the fastest accurate load that will work for what I'm hunting. Many of the ML loads I use are perfectly cappable of taking game out to 200+ yards, some even further with a little use of kentucky windage. The stoutest load I use is 130gr of pellets under a 300gr SST. I haven't tried this load with the 250 ShockWave but it would probably work with that also, but with sub MOA groups at 200 yards using 100gr of 777 2F, I see little reason to increase.

The bottom line is whether your gun (and shoulder) can handle the load and, more importantly, will it shoot accurately. No matter how fast it's going, if it doesn't go where you want it to, it's just a wasted shot.