I would agree with all that Shawn says, a muzzle brake works on two basic things, 1 being muzzle pressure and 2 being that the brake needs to have the surface area for that muzzle pressure to act against to counteract the recoil energy generated by the rifle.
looking at muzzle pressure, the more the better when getting a muzzle brake to work effectively and efficently. For example, take a 7 lb rifle in 300 WSM and another 7 lb rifle in 300 RUM. IF you use the correct break design, the 300 RUM will often have no more and sometimes even less felt recoil then the much smaller 300 WSM, why, the RUM has a huge advantage on muzzle pressure which forces the muzzle brake to work much more efficently to slow the rifle that has been set in motion from firing the rifle.
The larger the case capacity for a given bore diameter, generally, the higher the muzzle pressure will be. Even if the muzzle pressure is the same as a smaller chambering, the muzzle gas volume will be much more, another benefit of large cases with a muzzle brake.
Now to the muzzle brake. Surface area is critical. The more the better at having an effective muzzle brake to reduce felt recoil. Unfortunately, most of us want our rifles to be somewhat attractive and a huge brake just does not look good on most light rifles.
Still, its a compromise. As Shawn already mentioned, a diameter of around 0.750" is about as small as you should go with if you REALLY want to effectively reduce felt recoil.
On top of that, you want a partition style brake that has 3-4 large ports with solid partitions between each. They have solid bottoms so that you can shoot off prone positions without getting covered with ground debris as well. For reducing felt recoil, these are far better then brakes with radial ports all around the circumference of the brake. If your looking to reduce felt recoil, get a partition style brake.
SO which one should you go with, there are several out there. I currently use and endores only three brands of brakes. For conventional rifles I recommend two. THe Defensive Edge 0.750" 3 port brake and the Holland Quick Discharge brake.
The DE brake is slimmer but longer. THe Holland is shorter but slightly larger in diameter. Both have features that help limit muzzle jump. He Holland is more aggressive at this because it has three top ports designed specifically to control muzzle jump.
The DE 0.750 is a bit more suttle in controling muzzle jump as its partitions are relieved slightly at the top of each side of the port. This allows a slight amount of down thrust to he generated by the venting gas.
Many assume the more aggressive top ports of the Holland would be the best in a rifle with a high recoiling chambering. That in fact is not the case in a light rifle. Its a fine balance between controling muzzle jump and going overboard.
I actually prefer the Holland in smaller chamberings, 300 Win Mag class and smaller. In chamberings such as the 300 RUM, the Holland can produce far more down thrust then is wanted in a lightweight rifle. Just as muzzle jump is a problem, to much down thrust is the same problem, just in the opposite direction.
For the large chamberings, the DE is a better balance in my opinion as it produces just enough down thrust to keep the muzzle level but not so much that if you shoot the rifle off hand that you loose your sight picture because of down thrust..
You really can not go wrong with either but in your instance I would go with the DE .750 if you want a bit of muzzle jump control but not to much down thrust and good felt recoil reduction.
I use alot of both on customers rifles. I just build myself a light weight big game rifle in my 270 wildcat chambering. Doing the barrel break in with load development the 0.750" DE brake works to perfection. I can shoot the rifle offhand and when she goes off, the rifle simply sits there. No down thrust, no muzzle jump, no real recoil, just sits there. These are not full tilt loads but they are pretty hot compared to pretty much any big 7mm magnum out there. a 169.5 gr ULD RBBT loaded to around 3300 fps with top loads and recoil feels about like a 243 Win in this 8 lb rifle.
You can not go wrong with either brake maker. I mainly use Shawns brakes because they are affordable and do what they are supposed to do. You really need a partition style brake though and you will need a bit more brake diameter then muzzle diameter to get the most effectiveness out of your brake.
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