I have not touched base with Mic McPherson since COVID-19 began. I would recommend a simple little high-evacuation-rate brake on the straight walled 45/70, no matter how hot you might load them. I used bulk packed Remington 300 grain JHP bullets at 2300 fps for plinking from Winchester high-wall and Marlin lever rifles. No MB needed.
The difficult machining of the LAW MB is installing the gradual straight inside taper: step drilling followed by step reaming. I recommend using a leaded steel alloy such as 12L14 for the LAW MB, given the amount of stock removal required. That is what mine are made from with a nice chemically applied finish.
A photo of my 338-caliber LAW brake installed on a Schneider test barrel along with some shop-made barrel tuning devices is included near the end (Page 25) of the attached paper on rifle barrel vibrations. The data used comes from QuickLOAD(c) and my own (freely available) Excel spreadsheet calculations.
Wow, that is an extremely detailed write up! Thanks for the info, I'll need to go over that more closely when I get the chance. "Gradual straight inside taper" is a technique or profile I have never heard about. I have looked up nearly as much as I could on these brakes in the past 8 months or so and really only found pictures and brief descriptions such as "Lightweight Air Working" and "They're not just straight holes. There's a science behind it". What really intrigues me is that the people I spoke to say it almost makes their gun more quiet, or they didn't notice a difference in sound. It was my impression that muzzle brakes make guns much louder, so that seriously caught my attention. It also seems as if each one is a custom piece. No two pictures look the same. Some look like they need to be timed and others look like all the conical holes are evenly spaced. I spoke with the people over at Pacific Tool and they aren't even willing to change so much as thread pitch on the LAW brakes they make, but they do seem to have the hole shape correct. Another person who knows Mic McPherson had informed me that they are a "knockoff of his first generation LAW brake.", which also looked to not need timing. Same person is who let me know that McPherson is done gunsmithing, but he's still writing more books. It's a shame he didn't have an apprentice to teach his techniques to.
Last year I picked up a couple of the new Ruger Marlins. Went with the Trapper and SBL. Planning on taking the SBL out for a deer or elk hunt at some point, and wanted to be able to reacquire sight picture quickly, so I'll look into the high-evacuation-rate brake style you mentioned.
I know this is a long shot, but if I am able to find a gunsmith with the knowledge to make a LAW style brake, would that work well on a 300WM?
Would you have a more effective recommendation?
I'll be using that for deer, elk, pronghorn etc.
Here are all the variations I've found online, so far:
This one from Guns Magazine looks to need timing. Also looks like the holes go from cylindrical at an angle to conical at an angle.
This one is from a Marlin forum and installed on a 45/70. Looks like no timing needed and only conical drilling all the way through
Mic McPherson wrote another article in Guns Magazine and gave this picture for his 7mm RSAUM that doesn't look to need timing
You'll recognize this one of course. Looks more unique compared to the others and needs timing.
And finally here is the "knockoff" that Pacific Tool makes which looks like a hybrid of the 1st and 2nd pictures. Seems to have cylindrical holes at an angle that open up into conical holes at an angle, but no timing needed