I finally got my Ultra 5 after a 10 month wait. Main reason I got it was after personally witnessing several Ultra 5s on 20" and 24" 6.5 Grendel AR15s, which is a wicked-quiet combo. Ray and Bill Alexander noticed that the Ultras in 6.5mm might be too efficient at suppression for the AR15 and its bolt carrier vents, causing more noise at shooter's ear from the supersonic venting, and that the 30 Cal was probably the way to go for the AR15.
Against normal recommendations, I wanted to push the limit with the Ultra 5 because of how impressive it is in terms of weight and compactness. I had a hunch I would be happy, and I have to say that I am more than pleased with the noise level suppression from a 12" 6.5 Grendel so far.
Shooter experience is very pleasant, very smooth, no bark-like effects like I've heard from Surefire Mini or the OSS cans. For my purposes, the suppressor is there to reduce muzzle blast and offensive noise first and foremost.
I've also grown weary of the heavy cans out there attached to the end of a lightweight AR15, drawing back to experiences with the KAC QD cans, my Ase Utra Jet CQB can that I had for a while in Europe, and other heavy alloy suppressors.
I went with brake attach. This suppressor is really doing exactly what I wanted.
To regulate back pressure, I'm using a Bootleg Adjustable Bolt Carrier, which has a 4-way position selector that is accessible through the ejection port when the bolt is in battery. There is no need to disassemble or field-strip the upper. Just use a small flat head driver, and rotate accordingly.
Testing 2 different factory loads so far suppressed, I got them both ejecting smoothly at 4 o'clock using the full suppressed position. This was with 90gr TNT and 120gr OTM, both loads from Federal in the American Eagle line.
To give an indication of back pressure, the gun has cycled 100% so far in low round counts with 123gr Hornady BTHP American Gunner. With the 90gr TNT unsuppressed, I think the Maxim PDW action spring is too stiff, so it short-stroked with that load.
As soon as I attached the suppressor, 90gr TNT ran like a raped ape on all 4 gas settings, as did 120gr OTM on position 4. I fully expect 120gr OTM to run unsuppressed as well since there is more back-pressure into the system with a longer 120gr bullet resisting being driven through the barrel, unlike the 90gr flat-based TNT which needs to be punted out with fast powder.
Unsuppressed, I'm getting an average mv of 2670fps with the 90 TNT (5rd sample).
Suppressed, I'm getting 2683fps (9rd sample).
With 120gr Federal OTM suppressed, I'm getting 2384fps (11rd sample).
Once I choked the gas selector to the fully suppressed position, I can no longer see telltale signs of brass soot coverage like when it was fully open.
For those looking to do SBR or pistol Grendel suppressed, hopefully this can save you some trouble.
