DC... We built a recoil sled years ago to test different brake designs. We videoed each design, and had a tell tale on the sled. That was when we noticed how much torque was involved in recoil. We tested many different designs, and also tested the same design at different exit diameters from .007" clearance up to .060" Our sled which could easily differentiate between different brake designs could not measure the difference in recoil reduction between a .007" hole and a .050" hole on the same brake, of a good design.
.020 will work fine as long as you do not have a bunch of edges with surfaces 90 degrees to the bore line, and your brake material is above 30 rockwell on the C scale.
KDF breaks to my knowledge all come with a small hole that needs to be sized accordingly if the breaks hole was too small it was the gunsmiths fault!!! I have one on my 25-06 and it seems to work very well. If the gunsmith does his work properly you don't need a monster hole. A big hole is only a bandaid for sloppy setup work!!! By the way I saw a KDF break that a guy did himself and forgot to ream the hole to proper size. The 30 cal bullet tore the end off of the break. Any burrs on these breaks are a combination of sloppy machining and then having a guy that owns it shoving something through the holes in to take it off pushing the burr back into the path of the bullet. KDF breaks=seeing red mist!!!
H-Bar ...The size of the hole is not necessarily corellated to the "Quality of the Machine Work". It is however corellated to the accuracy achieved. It is also true that if you do not have coaxial alignment of the bore when boring the final diameter of the brake, you would have to make it larger than needed to keep the bullet from scraping the brake.
KDF makes a mediocre brake, no better than the New Holland. The recoil reduction is driven by the brake designer, the ultimate accuracy is determined by the installer of the brake.
S1, you seem to be very knowledgible on different breaks. I have been looking for a break that does not increase the noise. BP-TEC claims to make such a break. On their web site www.bp-tec.com , their first page says " no additional noise ". Are you familiar with this break, and if not would you look at the info on their site and offer your comments. They have gone so for as to say they would refund the money if the noise is greater.
I just tried the KDF on the "other" Tomahawk I have, also built by Ray Romain. It is identical to the one I sold Jake, except it it SS instead of CM. It is a very tight fit with a 240SMK, but as long as it is straight, the bullet slides thru without any interference.