It actually works - OpticsPlanet Exclusive Maxim Defense Industries RDB Roller Delayed Blowback System

I regretted buying the Daniel Defense PCC at first. It's an excellent carbine, but it is just direct blowback. The hydraulic buffer softened recoil considerably but didn't do anything for muzzle rise. When I saw this roller delay buffer, I thought, "No way it can be that easy." But I had to try.

It was that easy.

This thing really works. It makes a massive difference. The only downside is that it becomes hard to charge (hard to pull the charging handle back because you have to overcome the rollers...hence "roller delay"). It's very hard with one finger (relatively) but pretty easy with two fingers (one on each side of the charging handle). To me that's not really a downside, just something to remember. In any case, it's well worth it. Without any recoil mitigation, it keeps all hits within 1/2 to 1/3 of a USPSA A zone at 10 yards. With recoil mitigation (good, solid grip), that area shrinks. I use mine with a comp, but without the roller delay buffer, the comp didn't do all that much.

So now I love my Daniel Defense PCC. It's a night and day difference from stock.