The TBAC Ultra 9 is almost always my first choice if it'll work, but the 7 may suit you better if you only have the one. I use their 9" and 5" cans in .30 and 6.5. If you aren't gonna use this on a .30 and don't plan to, then get it in 6.5. With the TBAC you'll have to let it cool between strings. You can't do mag dump after mag dump with 'em. Firing 5.56 in it won't affect it. This is the go-to can for precision and low weight. It has a thread-over brake design, so it has all the advantages and none of the problems of a direct thread can. It's not true QD, but it's fast enough and quieter than QD, no ratcheting sounds. The 5" can is an actual hearing safe suppressor, but just barely --it's damn short too, only adds like 4" and is better than a moderator. Almost weightless on the end of a rifle. I use it more than I thought I would. The 9" is just amazing, but a bit long for some rifles. Not to mention the owner is a member here and frequently answers questions regarding them.
Elite Iron makes cans in 6.5 as well as .30 also, and he also uses a thread-over brake design, however, his cans are make of solid 316 and can handle more abuse. The thread-over design makes it mount solid like the TBAC. Elite Iron cans are well made but not over priced. His lower prices are not an indicator of performance or construction, although he does pass on some savings by using 316 vs. exotic alloys. He claims 316 is not only sufficient, it's one of the better materials; I tend to trust him as he's an honest guy and he's also a metallurgist by profession. FWIW, never heard of an Elite Iron can taking a shit.
The Sico Saker 7.62 is a solid mounting true QD can. No threads, it ratchets on and locks on with a cam behind the mount. Well thought out design, mounts solid and doesn't move, comes with more options, accessories and mounts than any other can I know of. You can get different size end caps; they have 5.56, not sure about 6.5 but you could easily take a 5.56 and bore it out. Some are specialty end caps, like flash hiders or breachers. I understand the 7.62 can is quieter with 5.56 than the dedicated 5.56 can, which I have. It is a bit bigger. This is a solid can that can also handle abuse.
KAC QDC is a fairly light, pretty accurate, indexed, true QD can. It's also expensive, and given there are other cans for less that'll suppress better than -28dB, this may not be the one. It's a nice can though and worth a mention.
There are bad choices! AAC makes a great can, but I can't recommend those 51T mounts to anyone. The 90T I hear is better, but not risking it. CS is historically horrible. Then you have a lot of small shops that are just cutting cheap, basic cans, many using aluminum, then you have others, gimmicky as hell and promising the world. Owners vary from honest to "will lie about anything to get a sale". So you can go wrong with both well known and small time or new shops as easily as you can go right if you don't do your homework, especially considering you are mostly buying blind here and are generally forced to go off someone else's experience with it.
In all cases, I've found those PRI Gasbuster charging handles to be worth it on AR's with suppressors. I like the combat latch model. They don't stop gas leaking out, but are the difference between having stinging gas in your eyes or not.
Good luck!
