if u want it to fit perfectly you should probably measure your own barrel..
what style of brake are u having made? the common practice is to thread barrel, install, bore brake for caliber and turn the out side OD to match the barrel once installed
The brake should be installed on the barrel and then turned down to match as closely as possible. Often the barrel diameter is not concentric with the bore so if you want it to be 'seamless' the barrel and brake will have to be final polished while assembled... then you can achieve what appears to be a one piece barrel/brake.
Hard to tell brake from barrel...
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