It is best to get the biggest diameter threads cut that you can for that particular barrel. I read a very interesting article on this in another forum. This auther / gunsmith has found that when smaller 5/8-24 threads were cut on the barrel, he was seeing what he described as " trumpeting" in the area in the very end of the barrel bore were the threads were at. He could fit a ground pin that was .0015 larger than the bore diameter into the first 1/2 inch of the barrel, right where the threads were . Now, this was on a 30 cal barrel . You may not see this happen on a barrel with a smaller bore diameter like a 22 or 6mm caliber that has more meat on it.
If you want to read the article, and see the video it is on 6mmbr.com in the gunsmithing section, april 2nd it was posted i think.
Another option would be a clamp on brake. I just got one from Witt Machine. It works great, and no gunsmith needed. Lots of good reviews on youtube on them. I tightened mine more than the 7inch pounds that they suggest.
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