Thanks to everyone.
I don't remember exactly "where" I read the things I mentioned, but it was on the net of course, in various forums while I was searching for information. I trust these forums more than others and that's why I asked you guys. I have little knowledge about such things, but I have a strong desire to learn.
If suppressing my .680" barrel is not a good idea due to thickness, then I will just discard that idea. By the way, I just now measured the end of the barrel (not 6 inches from it) and it measures .650".
here are yet more questions.
(1) I have another rifle, a CZ 527 in .17 Remington that has a heavier 24" barrel, which is actually their varmint model. The rifle is super accurate and I have considered suppressing it since it is a very loud one. The barrel end measures .700", but a few inches from the end is considerably thicker since it tapers quite a bit. I understand that the usual thread size for 22 caliber and below is 1/2x28", so would that barrel work fine with that thread, or should I use another thread?
(2) If I understand correctly, using a larger can (30 caliber) on a 22 caliber or less may not suppress as much as using a can more caliber specific. Is that correct?
(3) Another rifle I would like to suppress is a Dtech 6x45 that has a 20" barrel and measures .720" at the end.
What say ye about threading these two barrels? Thread size etc.?
(4) If building my own upper and purchasing a barrel that already has a 5/8x24" thread for a flash hider (6.8 SPC), is that all I need to screw on a can too, or do I need some sort of adapter. Will the can screw up tight enough or the proper distance onto the barrel threaded for a flash hider?