LW50 is actually one of the best barrel steels around. Pretty much overkill though for a regular muzzleloader. Ultimate Firearms uses them. My NULA has a Douglas Premium XX chromoly barrel. Its probably my favorite just because its not overly fussy and butter smooth.
My next barrel will be a Brux. They have been making lots of cut rifled ML barrels lately for several of the custom builders. Pricing is pretty similar to what Pacnor wants for a button rifled barrel.
Western does list load data upto 500gr and around 54gr by weight. Its under the cartridge data. You can get a pressure estimate simply by choosing a load with 100% density or slightly more. They dont have load data for 45cal MLs either yet we all know it works. Just ask the guys tearing up the targets at Friendship's Inline matches.
I would say most of them are shooting a max load with a 300-325gr jacketed bullet shot sabotless. In the past they were using more than Westerns max 120grV load until the rules were changed.
Myself and a few others here are shooting around 80grV (54gr by weight) and upto a 480gr conical in our fast twist 45s. Our plugs though have a 5/32" flash channel using either a Savage type vent liner or tungsten carbide bushing. BH209 is really hard on the flash hole with higher end loads. Once the flash CHANNEL fills with some carbon and/or the flash HOLE erodes its murder on the primers. There is not enough volume left in the channel to handle the increase in pressure.
A short plug makes this even worse but at the same time slows flash HOLE erosion. My NULA plug's flash hole is still like new after over 1000 shots BUT it also seals nearly perfectly. Im shooting loads in it that approach 35kpsi. IMO the key is fully supporting the primer AND as little blowby as possible. About the only way to achieve that in a break action is a slight .030-.050 crush on a primer and as much of the primer in the primer pocket as possible. My NULA seals (head spaces)on the rim of the primer similar to rimmed centerfire.
The problem comes in when you compare the lengths of primers. A Rem STS is much shorter than a Win209. If you get a slight crush on a STS primer you will get way too much on a Win209 in a break action. The rifle might fire when snapped shut. Ive seen it happen. If you get a slight crush on a win209 you will get none on a STS and it will leak badly....Been there too.
Savage went another route with the MLII. They sealed on the sides of the primer but thats even worse IMO. OD and taper varies just as much as length. Its not terrible if you hand fit your plug to your primer but its still nowhere near as clean as my other plugs.
This is what a good seal looks like. These primers are from one of my Knights with a slight primer crush and some really heavy loads. Blowby is basically zero even with a 385gr bullet and 120grV of BH209. I was testing this Lehigh 17-4 plug with WinT7s just to see how well the plug functioned with mild primers....Flawless