Posted in Benchrest also, but hoping for more eyes here. I'm chambering a 6.5 Creedmoor, and doing the muzzle threads. I was going to thread 5/8-24, since that's mostly what I'd thread 6.5 to .308 with, but it occurred to me that since the brake diameter and muzzle diameter are so big, I might want to go to 3/4-24 or 7/8-24 or even 1"-14. I'm making the brake, or I'd just pick the brake and thread to match. What do the benchrest guys do on small caliber rifles with large muzzle diameters? Is there agreement on what's more accurate or more effective?

No idea but intuitively you want to make the threads as large as possible; less to turn down; less time; equals less money. You are making the interface part anyway so that is fixed.
Accuracy and effectiveness would not be affected either way.

How many BR guys use brakes ?

i'd do 1"-16 .. as that's the barrel thread for several actions...

it could be broom stick threading, for all it matters, as the alignment and class of fit matter more.

are you looking for a smooth profile? that leads one set of choices -- or a "tank brake' ...

Thanks guys. Big as possible makes great sense, and 1"-16 is as big as possible but still gives me plenty of shoulder over minimum .050 a side that you want on a muzzle brake.

It's going to have 1/4"x7/8" ports with a flat cone at the bottom of each port facing back at a 45 deg angle like most of the PRS style brakes, but I haven't decided if it'll be 1.25" to match the barrel or taper out to 1.5", but I'm leaning toward barrel width.

Since the rifle is going to weigh a ton and it's only a 6.5 Creedmoor, have thought about just doing radial brake, but probably will go ahead with the PRS style.

RCraig, I don't know how many BR shooter's use brakes. I know Clay Spencer and most of the other BR gunsmiths have them as a standard offering. I believe they're prohibited in some classes and confined to radial style brakes in certain other ones. No idea of the percentages, but it's not zero.

Pretty sure that with a 6.5 and full bull, a brake will do zero but add blast.