I picked up a MP5F on the boards recently and when I tried mounting my AAC evolution 9mm can, it would insert but not turn. Prior to this I tried running it in full auto and no luck. Seller said the bolt was FA and sure enough it wasn't. Now I'm thinking I was sold a hack job. Long story short I contacted AAC and was told that their tri-lug mount is knurled and won't fit the MP5 but on the site is specifically says it will work.
Just for the record it did mount on my Octane .45
EVO-9™/ECO-9™ Triad Adapter
Not sure of the specifics of your setup but I run a Tirant 9s on my Dakota Tactical D54 with TRIAD ADAPTER FOR TI-RANT SILENCER
Triad adapter for Ti-Rant silencers
shows out of stock but would give AAC a call for ETA
Lol no Tony I won't do that, he specifically told me not to bash him if I'm not happy, not kidding either. I tried contacting him a few times with no response.
Most of the time when a 3-lug suppressor wont seat far enough to lock it is due to the distance between the back of the lugs and the cocking tube dust cover being to small. There are a combination of things that can contribute to this situation both firearm and suppressor related. Have you checked to see if the back of the 3-lug adapter is touching the leading edge of the dust cover when you press down to collapse the spring in the adapter? Remove the cocking tube dust cover by pressing in on the plunger. After its out... try to mount the suppressor. If it goes on and locks, that gives you a starting point for remediation. Even the dust covers can be found in varying thicknesses, believe it or not. I even turned the face of one down in my lathe a few thousandths of an inch and that's all it took.
I run a Gemtech Trinity with 3 lug on both by MP5K-N and MP5F both German builds (Ralph sir/Ralph jr at RDTS)
Fit's perfect, I do have to push in deep to turn. Both run exelent in full auto with and without suspressor.